Description and Designation of Vegetation vs. Biotic Communities: The Nature Conservancy and the United Nations Systems of Vegetation Classification vs. Brown et al. Biotic Community Classification
|Range Type: Defined and Described|
|The term "type"-- as a unit of vegetation classification (often interpreted as a taxonomic unit that attempts to show ecological relatedness)-- as noted above has had long and widespread usage. As used by range, pasture, forest, and wildlife specialists type has often been accompanied by adjectives that denote specific uses and/or the basic kind of vegetation. Examples commonly encountered in Range Management and Forestry literature include: range type, forest type, cover type, range cover type, forest cover type, range vegetation type, vegetational type, grazing type, dominance type, dominance community type, rangeland type, rangeland cover type (Zon, 1906; Clements, 1909; Clements, 1920; Stoddart and Smith, 1943, 1955; Society of American Foresters, 1950, Wegner, 1984; Baker, 1950; U.S. Forest Service, 1964; Westveld, 1939; Weaver and Clements, 1929, 1938; Polunin, 1960; Spurr and Barnes, 1980; Mueller-Dombois and Ellenberg, 1974; Whittaker, 1975; Holechek et al., 1998). All of those in this list are, roughly speaking, basically synonyms.|
|There has been no standard
or universally accepted definition of “type” even though it has a long
and useful history in Range Management and Forestry. The term as a unit
and concept of vegetation has been used rather consistently given the
numerous systems of vegetation classification (generally used synonymously
unless one is an extreme taxonomic “splitter”). There remains, however,
considerable confusion as to where forest and range (= grazing= vegetation=
cover= dominance) type fits into the hierarchy or organization of vegetation.
“The terms grazing type or vegetation type are not distinct in their
usage “ (Stoddart and Smith, 1943, p. 66; 1955, p. 46). This situation
has not changed in the half century hence.
|The current Society of American Foresters Forestry Handbook (Wenger, 1984), the standard reference for foresters in the United States and Canada, still list for range classification the "eighteen broad standardized range types" first adopted by the Western Range Survey Conference on 24 April, 1937. These range types are named based on "[t]he apparent dominant vegetation lending the type its 'aspect' or general appearance" (Wenger, 1984, ps. 751-752). Though referred to in Wenger (1984) as range types these vegetation units are also called standard forage types and grazing types. They are designated as to aspect as determined by the dominant species and "have no ecological basis" (ie. they are not designated, at least not consistently, on the basis of "potential natural vegetation" nor "the successional state of the vegetation").|
|Most importantly, it should be emphasized that these U.S. Forest Service range (= grazing) types are not the same as forest cover types or other related but distinct classification units used in the Society of American Foresters Forest Cover Type Classification. Nor are they in the United Nations Education, Scientific and Cultural Organization classification based on physiognomy and structure of vegetation; the Potential Natural Vegetation Classification of A.W. Kuchler; the Habitat-Type Classification of R. Daubenmire; or Ecosystem Classification as, for example, by the U.S. Forest Service. These latter classification systems were described briefly by Wenger (1984, ps. 12-16).|
|Likewise, not all forest types are the same. Terms in the above list are roughly synonymous, but there are various categories of forest type and these kinds of forest types differ specifically and substantially from each other. The kind or category of forest type of concern herein is forest cover type, the one most commonly used to describe existing or present forest vegetation. Forest cover type may or may not coincide or overlap with other kinds of forest types discussed below. Apparently all types of rangeland vegetation are of the same category: rangeland cover types (the equivalent of forest cover types according to Shiflet [1994, p. ix, xi]). There are not parallel or equivalent units of rangeland vegetation comparable to the other forest types, but only to cover types.|
|The Nature Conservancy and the United Nations Systems of Vegetation Classification|
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|The fundamental concept of vegetation type as either 1) a broad and large unit or 2) a general term for vegetation has been widely accepted, but the precise placement of this unit within the structure or organization of vegetation and the hierarchy of various vegetation classification systems has not been agreed upon. An example is the recent comprehesive vegetation system in the United States, The National Vegetation Classification System, under aegis of the The Nature Conservancy in cooperation with several other organizations including the Ecological Society of America's Vegetation Classification Panel, US Forest Service, Natural Heritage Programs, and Conservation Data Centers. The National Vegetation Classification System apparently used "vegetation type" as the generic catch-all term for all hierarchial units (= levels) within its scheme and yet not as the formal designation for any specific unit unit ov vegetation (Grossman et al., 1998, Volume 1. ps. 12, 18, 37, 46, and 48).|
Nature Conservancy hierarchy of vegetation classification system (NVCS)
for terrestrial ecological communities is:
first four units are physiognomic levels and the last two units are
Vegetation type and/or cover type units are obviously absent.
draft (do not cite)” of “An Initiative for a Standardized Classification
of Vegetation in the United States” by the Ecological Society of America
(ESA) Vegetation Classification Panel (1997) stated unequivocally
that there is a lack of agreement on terms used in describing and
science has had neither consensus nor national direction for its basic
vocabulary” (p. 9).
Panel working draft further commented:
“Agreement on terms often is not possible without agreement on the concept to be used, or at least respect for alternative perspectives on concepts” (p. 15)
|The working draft of “An Initiative” included six lists of terms used for units or levels of vegetation as found in Vegetation Science literature. For terms and definitions used at level of “specific upper-level floristic type” there were seven listings of terms and/or definitions for terms. Four of these were for cover type and these four were among the bottom five “in order of preference expressed by Terminology Work Group Members” (ESA Vegetation Classification Panel, 1997, ps. 11-13). Listed last (least preferred) was the definition proposed in 1989 which according to the Panel was the National Terminology Project of the Society for Range Management (incorrectly cited by the Panel under the former society name of American Society of Range Management which was changed almost 30 years ago). The only preferred term by the Panel for the upper level floristic type was alliance for which there were five proposed definitions which were ranked.|
|Likewise for “specific lower-level floristic type” the term and definition least preferred and listed last in the Initiative working draft by the Terminology Working Group of the ESA Vegetation Classification Panel (1997, p. 14) was vegetation type as defined by the “(ASRM 1989)”|
|In the introduction to terminology standards in the Initiative working draft, the ESA Vegetation Classification Panel (1997, p. 9) observed that the Society of American Foresters and Society for Range Management “used vegetation classification systems”. “These two societies ask their members to use their official published terminology (SAF 1977, ASRM 1989), which raises related questions for the ESA.” [The 1989 citation was for the National Terminology Project, Preliminary Draft, and not the 1989 SRM third edition of A Glossary of Terms Used in Range Management.]|
|The twenty members of the ESA Vegetation Classification Panel were listed as from universities (nine members) and federal agencies like the Bureau of Land Management, US Geologic Survey, US Forest Service, and Agricultural Research Service. Scientific/ professional societies such as the SAF, SRM, and The Wildlife Society were not represented directly or per se (at least these organizations were not listed or associated with Panel members).|
introduction of the U.S. National Vegetation Classification (USNVC)
System The Nature Conservancy did compare or relate (briefly) their
system to the Society of American Foresters (SAF) cover types:
“SAF cover types are ‘a descriptive classification of forest land based on present occupancy of an area by tree species’ (Eyre 1980). By contrast the USNVC uses all vascular plant species present in a community to help define vegetation units. Where dominant tree species are also diagnostic for a community type, similar, though not identical, units are identified by SAF cover type and USNVC alliance. Examples include the Jack Pine Forest Cover Type and the Pinus banksiana Forest Alliance, and the Post Oak-Blackjack Oak Forest Cover Type and the Quercus stellata-Quercus marilandica Forest Alliance. In other cases, the SAF cover types are more broad-ranging over both structural and environmental gradients than are the alliances recognized in the USNVC. For example, the Black Spruce Cover Type is separated by the USNVC into an upland Picea mariana Forest Alliance, a Picea mariana Saturated Forest Alliance, and a Picea mariana Saturated Woodland Alliance. The primary difference between these systems is that the SAF cover types are defined exclusively for forest vegetation, whereas the USNVC classifies all terrestrial vegetation.” (Grossman et al., 1998, p. 44).
|No reference was made by The Nature Conservancy (Grossman et al., 1998) to the SRM rangeland cover types. Given that publication of descriptions of rangeland cover types as, noted by Shiflet (1994, p. ix), was intended to serve as a “companion” to the SAF forest cover types published in Eyre (1980) it would seem that both rangeland and forest cover types (range types) would correspond roughly to one or more USNVC alliances. This is not a “perfect match” because, as noted by Grossman et al. (1998, p. 44), the SAF forest cover types were “based on existing tree cover”, “… forests as they are today—what the land manager finds on the ground and must deal with” (Eyre, 1980, p. 1). By contrast a higher proportion of the rangeland cover types, while described as “existing” and “today”, are climax or potential natural vegetation. Quick glance at the range vegetation types described in Shiflet (1994) reveals that most of these are what seem to be, to best existing knowledge, the highest expression of vegetation development possible under existing environments. This includes human-induced “new climaxes” (disclimaxes) that have thoroughly naturalized such as the California annual range type. The SRM rangeland cover types would likely correspond somewhat less closely to the USNVC alliances because The Nature Conservancy classification scheme is applied to existing vegetation: “The focus of the USNVC is on existing, rather than potential, vegetation” (Grossman et al., 1998, p. 16). Yet this was not all that clear or specific because later on Grossman et al. (1998, p. 16) also stated: “… efforts have been primarily focused on mid- to late-seral, natural/near natural vegetation”.|
The Nature Conservancy (Grossman et al., 1998, ps. 7-8) and the Society
for Range Management (Shiflet, 1994, p. xii) cited classification
systems of potential natural vegetation, noting especially the well-known
maps of A.W. Kuchler, and clarified that their units of vegetation
sometimes coincided with climax or potential natural vegetation. Shiflet
(1994, p. xii) was explicit:
of the cover types included here may bear some resemblance to those
of Kuchler, but most do not since they are, for the most part, the
result of human influence since the mid-1880’s. If plant succession
were allowed to take place unimpeded, in time the vegetation of these
should approximate those communities described by Kuchler”.
Society of American Foresters offered a similar assessment for the
forest cover types it described:
“Without disturbance, the present forest would tend to move toward the Kuchler potential and some SAF descriptions of climax types strongly resemble Kuchler’s phytocenoces” (Eyre, 1980, p. 3).
|In conclusion, the range cover types (both SRM rangeland and those SAF forest cover types useful or usable as range) correspond to the USNVC alliances with the main difference being that the alliances are more specific or restrictive than cover types (ie. cover types would often include several alliances as noted by USNVC authors).|
|The USNVC System was offered as an International Classification of Ecological Communities (though it was restricted to vegetation— included no fauna— and limited to the United States). It obviously had its origin in the United Nations Educational, Scientific and Cultural Organization (UNECSO, 1973). Grossman et al (1998, p. 43) also cited Driscoll et al. (1984), but the USNVC System is that of UNESCO with modifications as described below.|
UNESCO system in turn was a direct application of the Physiognomic-
Ecological Classification of Plant Formations developed by Ellenberg
and Mueller-Dombois in 1967 and shown in detailed revised form in
Mueller-Dombois and Ellenberg (1974, ps. 466-488). The vegetation
hierarchy of the Ellenberg and Mueller-Dombois scheme is:
Further Subdivisions .
|The Nature Conservancy USNVC System retained the first three vegetation units of UNESCO/Mueller-Dombois and Ellenberg, inserted Formation Subgroup between Formation Group and Formation, and deleted Subformation while specifying Alliance and Association as the first two of Further Subdivisions (see above listing of USNVC hierarchy)|
USNVC System also differs from the Mueller-Dombois and Ellenberg Physiognomic-Ecological
System in that the former is based almost solely on the single factor
“A pivotal decision made by Conservancy ecologists was to develop a terrestrial classification system that was based primarily on vegetation” (Grossman et al. 1998, p. 14).
|After reviewing single-factor vs. multi-factor classification systems The Nature Conservancy cited Mueller-Dombois and Ellenberg (1974) and decided upon a single-factor system based on vegetation “because it generally integrates the ecological processes operating on a site or landscape more measurably than any other factor or set of factors”.|
UNESCO Structural-Ecological Formation System is also based primarily
on vegetation but “some environmental-geographic information” is incorporated.
It’s hierarchial levels “are real vegetation units” but the system
is “artificial” (Mueller-Dombois and Ellenberg, 1974, ps. 163-164).
Mueller-Dombois and Ellenberg (1974, ps. 157-168) reviewed structural
vegetation units and systems like UNESCO. In this context vegetation
structure refers to “physiognomic criteria” such as plant life (=growth)
form (which is the most important), plant size or height, deciduousness
vs. evergreenness, and leaf features (eg. shape, size, and texture).
These are essentially the same features of vegetation physiognomy
given by Warming (1909, ps. 137-140 passim).
They have traditionally formed the basis of distinguishing formations:
“Plant communities that are dominated by one particular life form, and which recur on similar habitats, are called formations [in the physiognomic-ecological sense]” (Mueller-Dombois and Ellenberg, 1974, p. 157).
|This has been the European tradition of defining formations physiognomically. By comparison the American— actually Anglo-American— perspective “has been to define the same concept [formation] geographically and climatically”. This is the classic Clementsian interpretation in which several physiognomic units occurred within the same formation (eg. units of forest within grassland). The European view of this scale of vegetation, the Clementsian formation, was “ …not a formation, but a vegetation region”. “A vegetation region usually contains a mosaic of actual vegetation types” (Muelller-Dombois and Ellen, 1974, p. 157). The “zonal or regional vegetation mosaic” was recognized by Clements, but in the European view he confounded their use of formation by interpreting some physiognomic units as successional (seral) stages of what he interpreted as the regional or climatic climax, the monoclimax, (or as preclimax or postclimax to the prevailing climatic climax).|
A longer historical examination suggests that the dichotomy between European and Anglo-American views of formation and physiognomy is not as clear as Muller-Dombois and Ellenberg (1974) suggested. Warming (1909, p. 139) credited Grisebach with the introduction of the term “formation” or “vegetative formation” in 1838 “in the form of ‘phytogeographical formation’”. The original coinage and usage by Grisebach with the adjective of “geographical” is clearly consistent with the interpretation of Clements suggesting that it was the European and not the American (Clementsian) school that took formation away from it’s seminal usage. This is further suggested by the definition by Warming (1909, p. 140):
“A formation may then be defined as a community of species, all belonging to definite growth-forms, which have become associated together by definite external (edaphic or climatic) characters of the habitat to which they are adapted”.
|The inclusion of both soil and climate as a basis for formation is consistent with both the Tansley polyclimax and Clements monoclimax views. Either way, Warming (1909, p. 140) used “the chief types of growth-forms as the prime basis of classification” for formations. Again, physiognomy is the basis of formations and life (= growth) forms are the primal criteria for physiognomy.|
|In continuing their review of vegetation classification Mueller-Dombois and Ellenberg (1974, p. 165) concluded that “most investigators consider floristically defined vegetation units as more useful than structurally defined ones”. Thus species composition, the floristic component, cannot be ignored in “any detailed study of vegetation”. The structural (= physiognomic) component of vegetation by itself is not adequate.|
|The Nature Conservancy (USNVC) team reviewed vegetation classification systems as three groups: 1) physiognomic systems (eg. UNESCO), 2) floristic systems (eg. Zurich-Montpellier or Braun-Blanquet and Daubenmire association/habitat type systems), and 3) physiognomic-floristic systems (eg. Dick-Peddie, [1993, ps. 35-45]). The USNVC System is a combination system that “uses both physiognomic and total floristic composition criteria”, “a hierarchial taxonomic structure with physiognomic criteria used at coarsest levels of the hierarchy and floristic criteria used at the finest” (Grossman et al., 1998, p. 17; USNVCS vegetation hierarchy shown above). The first (highest) five hierarchial vegetation units are physiognomic levels and the Alliance and Association are floristic levels (Grossman et al., 1998, ps. 20-26).|
|Hierarchial Classification of North American Biotic Communities- The System and Map of Brown, Reichenbacher, and Franson|
Currently (and probably for the forseeable future) the system of classification for North American vegetation that is both comprehensive and most consistent with the traditional biome-association-dominance type model used in Range Management and Forestry (eg. SRM and SAF cover types) is that of Brown et al. (1998). These workers specified that their classification was "a biotic-community approach" in contrast to "purely vegetative classification systems", but their seven-level system published as A Clsssification of North American Biotic Communities included examples only of the biotic community (fourth level) and the series (fifth level) for most communities and to the association (sixth level) for some communities (Tables 4 and 5, ps. 36-48). All of these were designated by dominant plant species. Association was defined consistent with it's usage traceable to the International Botanical Congress in 1910, but spatial scale of association was "more or less local" (Brown et al., 1998, p. 35) and thus not consistent with the Clementsian-Tansylian association that was by and large the scale, interpretation, and usage of association adopted by the professions of Range Management and Forestry. Brown et al. (1998, p. 35) specified that the sixth level refered to "a distinctive association" with such associations "generally equivalent" to the Daubenmire habitat type. The few examples of the association (sixth level) were "plant associations". Nonetheless, the series (fifth level) corresponded very closely with the SRM and SAF cover types. Brown et al. (1998, p. 14) stated that their "general series of actual or potential plant dominants" were referred to as cover types by the Society of American Foresters (and alliances by The Nature Conservancy).
As was explained above, cover types and alliances are not synonyms and are not really interchangeable or completely convertible/translatable from one to the other. Many (probably most) of the Brown et al. (1998) series were very similar and often essentially synonymous with SRM and SAF cover types. These two units of vegetation are far rmore similar to each other than is either to The Nature Conservancy alliance because Brown et al. (1998) series and cover (= dominance) types both are essentially Clementsian in origin and outlook while The Nature Conservancy classification system is fundamentally based on the Braun-Blanquet model (Zurich-Montpellier School of Phytosociology). Brown et al. (1998, ps. 9-12) briefly reviewed the approaches to vegetatation classification more commonly used in the United States (including that of The Nature Conservancy). They also explained how and why A Classification of North American Boiotic Communities had adopted the Clementsian biome and the terms/concepts of disclimax and subclimax.. They then explained "advantages of a biotic-community approach over purely vegetative classification systems" (Brown et al., 1998, ps. 12-14).
Brown et al. (1998, p. 12) stated that "Clements was a great ecologist" and "... many of his contributions remain valid in modified form". (This conclusion was enthusiastically shared by your current author as was made evident throughout this publication.)
The Brown et al. (1998) hierarchial classification system was highly recommended and extremely useful. The earlier publication, Biotic Communities- Southwestern United States and Northwestern Mexico (Brown, 1994), was even more utilitarian and applicable in classifying and describing flora-fauna communities and, especially, vegetation in that region of the continent.
Unfortunately, A Classification of North American Biotic Communities (Brown et al., 1998) did not include enough series to correspond with all SRM and SAF cover types. This limitation was especially noticable and problematic for North American grasslands. The Brown et al. (1998) classification however did include (without major emphasis) subclimax and disclimax plant associations as well as climax vegetation (Brown et al., 1998, p. 35-36). This was particularily useful for Range Management as the biotic community system included such important disturbance climaxes as the California annual grassland (Annual Disclimax Series) and former climax bunchgrass-shrub steppe depleted to cheatgrass range (Cheatgrass Disclimax Series). Here again, though, Brown et al. (1998) omitted the climax Stipa bunchgrass prairie of the Central Valley, Coast Range, and Sierra Nevada foothills. This omission was consistent with omissions in the published SRM cover types (Shiftlet, 1994) and U.S. Forest Service forest and range ecosystems (Garrison et al, 1977) and inconsistent with the potential natural vegetation mapped and described by Kuchler (1964). Interestingly, for the Kuchler manual describing the climax California bunchgrass prairie, California steppe, there was apparently not even a readily available photograph of this pre-Columbian grassland so that a U.S. Forest Service photograph of California foothill annual grassland was used (Kuchler, 1964, p. 48). This was the same photograph used to accurately illustrate annual grassland disclimax in the manual by Brown et al. (1998, Plate 62, p. 88)! This rather comic situation was symptomatic (and symbolic) of the fact that the disclimax grassland designation was a more correct one for practical management than the designation of the pristine-- and essentially "extinct"-- virgin range.
Brown et al. (1998) series and associations were also quite limited for conifer forests of western North America. This was especially obvious (and bothersome) for SAF cover types of the Northern Rocky Mountains. This situation may have been partly a result of the Brown et al. (1998) emphasis on climax vegetation whereas several SAF cover types were "based on existing tree cover", "... forests as they are today...", such that some of these types are transitory or temporary (ie. seral) to climax forest communities (Eyre, 1980, p. 1). That partial explanation was largely unsatisfactory however because: 1) Brown et al. (1998) classification did encompass units of disclimax and subclimax forest vegetation and 2) Brown et al (1998) omitted several distinct forest communities long recognized as climax by workers like the "great ecologist" Clements. For example, Brown et al. (1998, ps. 36- 38) omitted series and associations in the Rocky Mountains that applied to SAF cover types 212 (western larch), western white pine (215), western redcedar- western hemlock (227), and western redcedar (228) that are all parts of the larch-pine forest association (thus climax) recognized by Wesver and Clements (1938, ps. 503-504).
Overall, the Brown (1994) and Brown et al. (1998) classification appeared to be more relevant-- more applied and more similar-- to range and forest cover types as both a hierarchial system and designations/descriptions of plant communities (= vegetation) than those of The Nature Conservancy and United Nations. In some respects, the Brown et al. classification of biotic communities was also more comparable to the Kuchler (1964) map and manual of Potential Natural Vegetation (disclimax and subclimax of the former being exceptions). Kuchler units of vegetation served as the basis for Forest Service forest and range ecosystems (Garrison et al., 1977, ps. 1-3) and for comparisons with SAF (Eyre, 1980, p. 3) and SRM (Shiflet, 1994, p.xii) cover types.
|Associations and Consociations|
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|Mueller-Dombois and Ellenberg (1974, ps. 171-176) also reviewed floristic vegetation units and systems. Their format and brief historic analysis of floristic concepts allowed further comparison of the SRM and SAF range cover types to The Nature Conservancy USNVC vegetation units, and to pivotal perspectives leading to the development of vegetation type as used as a restrictive and specific unit in Range Management and Forestry. According to the brief review of Mueller-Dombois and Ellenberg (1974) there have been two fundamental floristic units and concepts in vegetation classification and description. These two “species dominance community-type concepts” are: 1) the sociation and consociation generally and 2) in specific usage by the Clementsian school, the association.|
On the European mainland sociation was seen as a basic unit of vegetation classification where a sociation was any plant community that essentially had a “homogenous species composition with at least certain dominant species in each layer”. Sociation was one of the lower units in the Clementsian hierarchy of climax vegetation largely based on or describing seasonal sequence or phenological aspects (hence “aspect”) (Clements, 1936, ps. 276-277, 281).
was a major unit of vegetation in both European thought and in the
Anglo-American (Tansley-Clements) school of dynamic vegetation (Clements
1916a, p. 120; Tansley, 1926, ps. 34-36; Clements, 1936, p. 274).
In the Clementsian model consociation
was “the unit of the association” (Clements, 1916a, p. 120) though
the association “is to be regarded as divided into definite groupings
of dominants or faciations” where faciation ”is the concrete subdivision
of the association” (Weaver and Clements, 1938, ps. 94-95).
The distinguishing or defining characteristic of consociation
was presence of a single dominant, one dominant species, or at least
a single major dominant if several domiants were present. In an abstract
sense each major dominant of an association was a consociation (Weaver
and Clements, 1938, p. 94). Tansley (1926, p. 34) explained that an
association usually had “more than one dominant species” or co-dominants.
The community (the unit or level of vegetation) within an association
formed by a single dominant species was the consociation. Pinus
ponderosa in the montane forest formation and Stipa
spartea or Agropyron smithii
within true prairie were used as examples of consociations in Weaver
and Clements (1938, p. 94-95).
and Ellenberg (1974, ps. 172-173) concluded that as a unit consociation
had “no universal applicability”. Consociation was difficult to use
in communities having high species richness or, conversely, a single
species “may become dominant under different habitat conditions” (ie.
when a single dominant species is used to define or delineate a community
type “very different habitats” may get grouped together). The first
difficulty is self-evident and an obvious limitation. The second condition
of lumping together different habitats is a ridiculous criticism,
at least at larger spatial scale (within the same or similar climate).
Yes, it is a true statement of the actual situation but: 1) vegetation
and not habitats are being classified, described, mapped etc. and
2) at that large scale (the first subdivision of a formation) “jillions”
of habitats are included and these habitats, in turn, will be subdivided
out at progressively lower, more specific levels. In other words with
regard to 2) no unit of vegetation is site-specific unless it also
includes habitat criteria, but progressively smaller units of vegetation
have progressively less heterogeneous habitats. Incidentially, recall
from discussions in the Range Site section that this same sort of
grouping together (inclusion) of different habitats in the same taxonomic
unit of vegetation is typical of the habitat type approach.
obvious difficulty with consociation was the confusion in the different
ways in which association
was applied. As with— actually originating with— formation, the vegetation
unit of association was applied differently in Continental schools
of vegetation than in the Anglo-American school (the predominate Anglo-American
perspective). As a concept
and vegetation unit, association has been second to none or only to
formation (or climax and, later, biome in Clementsian Ecology). Association
has been a— perhaps the— major unit and unifying concept in description,
classification, and mapping of vegetation. Association is traceable
to the early days of Plant Geography. Warming (1909, ps. 137, 144)
credited the origin of plant association (plantes associees) back
to Humboldt (1807). Warming’s Oecology of Plants (1909, English
translation) has often been regarded as the world’s first textbook
in Plant Ecology. In it Warming listed several other plant geographers
and ecologists who employed association (or its concept by other names).
He defined association as “a community of definite
floristic composition within a formation; it is, so to speak,
a floristic species of a formation
which is an oecological genus” (Warming, 1909, p. 145). Associations were “smaller, often more-localized subdivisions
or kinds of the formation” (p. 144). As was species to genus so was
association to formation. To Daubenmire (1968, p. 29) “the association
serves the same purpose in synecology as the species does in taxonomy”.
Daubenmire stated that there was a long-standing analogy of association
to species and that while “[n]either is susceptible to rigorous definition…”
both remain equally essential to their fields. Tansley (1926, p. 30)
succinctly put the association is perspective by describing it as
“the fundamental unit of vegetation”.
in Brussels the Third International Botanical Congress adopted by
official resolution the following definition of plant association:
… a plant community of definite floristic composition, presenting
a uniform physiognomy and growing [or “when occurring”] in uniform
habitat conditions” (Daubenmire, 1968, p. 27; Mueller-Dombois and
Ellenberg 1974, ps. 173-174).
a five page review of association Daubenmire (1968, p. 32) concluded
that association was “a type of climax phytocoenosis”. He then remarked
that “very little” climax vegetation remained (due largely to human-induced
disturbance) yet “each climax can normally regenerate itself repeatedly
following destruction” so it was the area
belonging to each association that is of ecological importance.
This area of one plant association or that had been in one association
or that had potential to regenerate that association was Daubenmire’s
habitat type (synonym, homoece).
if habitat type is equal to plant association (or previous or potential
plant association) and association is a subdivision of a formation,
the largest unit of vegetation in the original usage of the term,
then there is absolutely no way whatsoever that habitat type could
be the equivalent of or a synonym for range site, the smallest unit,
the most distinctive kind, of native grazing land. Given the historic
definitions of these vegetation units, the attempt to rationalize
the equivalency of habitat type to range site (discussed in the Range
Site section) seemed ludicrous to the present author. [It will be
explained below that the Daubenmire association was generally closer
to a subassociation of the Clementsian association, a unit more similar
to a cover type.]
the 1910 Botanical Congress definition, which was nearly verbatim
(with an addition or two) that of Warming, did not specify the basis
for delineating an association and the term/concept came to mean two
different things to the Continental and Anglo-American views of vegetation
(Mueller-Dombois and Ellenberg, 1974, ps. 174-175). In his last major
paper on the climax Clements (1936, p. 273) noted this difference
between the two schools of thought in defining association:
the climax concept this represents the primary division of the biome
or formation, and hence differs entirely from the generalized unit
of the plant sociologists, for which the term community
is to be preferred. Each biome consist regularly of two or more associations
Clementsian school retained the meaning of association specified by
Warming (1909, ps. 144-145) as a subdivision of the formation or as
species of the formation genus.
and Ellenberg (1974, p. 175) described the Clementsian association
as “the general plant cover in a given macroclimatic region (ie. a
vegetation mosaic)” or “more or less a climatic subregion”. The latter
description is apt because the formation was based on, determined
by, regional climate; the former description was not of an
association but of a formation which includes several associations.
Mueller-Dombois and Ellenberg (1974, p. 175) were correct, and specifically
so, in a synopsis statement:
climax was subdivided into a few ‘formations’ (regions) and each ‘formation’
was subdivided into two or more ‘associations’… Clements defined an
association floristically by joining the names of two regionally dominant
species and then implied that an association was a grouping of two
or more consociations”.
(1916a, p. 128) first used association it was a floristic subunit
of the physiognomically-developmentally derived formation. Fundamental
development and life-forms were the same for all associations in a
formation (these two features unified or served as basis for formation);
differences in dominant species distinguished the various associations.
In Plant Ecology Weaver and Clements (1938, p. 93) introduced
the association with this description:
climax formation consist of two or more major subdivisions known as
associations. These are climax communities associated regionally to
constitute the formation. The number of associations in a particular
formation is naturally determined by the number of subclimates within
the general climate of the formation.
Each association is marked by one or more dominants peculiar
of the most explicit descriptions of plant association was in Plant
climax formation falls readily into two or more major subdivisions
known as associations. Toward their edges these blend into each other
more or less, making a transition area or ecotone. The latter is broad
in the case of relatively level regions, and narrow in that of the
climax zones of mountain ranges. The associations have one or more
dominants in common, or at least belonging to the same genus, and
there is a certain degree of similarity as to subdominants also. Each
association consist of several dominants as a rule, though there may
sometimes be as many as eight or ten or more, as in scrub and chaparral.
Each dominant constitutes a consociation. It may occur alone, though
as a rule it mixes and alternates with the other dominants of the
same association This is the direct outcome of the similar requirements
of the dominants, and hence it is a guiding principle that two or
more consociations are regularly associated in the larger unit (Clements,
1920, p. 107).
view expressed by Clements came to be the
interpretation of most British, American, and Canadian ecologists
as well as those in nations with ties back to “mother countries” (eg.
South African ecologists like J.F.V. Phillips were largely of the
Anglo-American school). The various “schools” of ecological thought
were defined largely by geographic location. These were reviewed exhaustively
by Whittaker (1962). Shimwell (1971, ps. 44-62) also discussed the
different Schools or Traditions and drew pedigrees or lineages of
them. The English Tradition (Shimwell, 1971, ps. 47, 54) which dominated
Range Ecology and Forest Ecology during their formative years and
formed the foundation of modern Range Science and Forest Science can
be traced back through Clements (and to a lesser degree Tansley, C.E.
Moss, and H.C. Cowles) to Warming, Oscar Drude, and finally to the
fountainhead of August Grisebach, an oft under-rated plant geographer
who described vegetation types physiognomically and in relation to
climate and who was the first to use the term formation (Clements,
1916a, p. 116).
English-American-South African Tradition came to be known as the holistic
or organismic school of vegetation. It was clearly the “dominant species”
of ecological thought in its day and probably, though in less pure
form, today. A smaller, less influential school was the individualistic
or continuum school begun by the American ecologist Henry A. Gleason
and more or less perpetuated— at least experiment-wise— by Robert
H. Whittaker. Whittaker actually defied pigeon-hole categorization
being somewhat of a hybrid. He did expand the Gleasonian individualistic
concept through gradient analysis but as discussed above (Biome section)
he successfully reconciled Clements’ monoclimax and Tansley’s polyclimax.
This, plus his views on communities (Whittaker made much use of biomes),
would place him squarely in the Anglo-American “pedigree” (Shimwell,
1971, p. 54).
Gleasonian branch of the English Tradition (Shimwell, 1971, p. 54)
became known for its “individualistic concept of the plant association”
(Gleason, 1917; 1926). Allen (1998) contrasted the Clementsian
and Gleasonian associations by remarking that Clements used association
as an abstraction for a unit of climax vegetation while ignoring seral
stages leading to climax (as a subdivision of formation or climax,
association was not a seral unit). By contrast Gleason used association
as a concrete unit of vegetation based on species composition at an
instant of time and at a site while ignoring climax. Allen (1998,
p. 320) overlooked or ignored the fact that in his elaborate scheme
of vegetation units Clements (1936, ps. 278, 281) included as the
equivalent of associations the seral unit, the associes, which
was “the major unit of every sere”. (Clements was
always one jump ahead of potential criticism and covered about
every conceivable weakness in his pet theories.) Nonetheless, Allen’s
observation on Clements’ association being an abstraction was partly
correct because Clements (1916a, p. 126) stated that association was
used “in both abstract and a concrete sense”. “The general use of
association in the concrete has fixed it definitely in ecological
terminology”. On the other hand, Allen’s interpretation of the Clementsian
association as an abstraction seems to have been a view either anticipated
by Clements or made to him, and he seems to have denied it:
the formation is necessarily an organic entity, covering a definite
area marked by a climatic climax. It consist of associations, but
these are actual parts of the area with distinct spatial relations.
The climax formation is not an abstraction, bearing the same relation
to its component associations that a genus does to its species” (Clements,
1916a, p. 127).
Shimwell (1971, p. 53) commented on these words and concluded that Clements “conceived the formation not as an abstraction”.
(1950, p. 44) concluded that Clements (1928) used association “in
a somewhat abstract sense to cover a section of a formation occupying
a subclimatic zone and therefore having climax dominants dictated
by that subclimate…”. Nichols
(1923, ps. 15-17, 172) discussed the abstract vs. concrete concept
of plant association. He cited a
resolution routed by letter to 85 ecologists (“mostly botanists
and foresters and mostly members of the Ecological Society of America”)
in 1921 which read in part: “That the term Plant Association be recognized
as applicable both to the abstract vegetation concept and to the concrete
individual pieces of vegetation on which this concept is based”. Of
the 76 respondents, 67 favored adoption of the recommendation (Nichols,
1923, p. 15).
his part, Clements (1916a, p. 117) concluded that the formation of
Grisebach and the association of Humboldt “meant practically the same
thing by their respective terms”.
Clements (1916a, p. 118) quoted Moss (1910) as dividing formations
into associations following “many previous authors” but these were
traced back to Warming as being the first to publish this subdivision
(Clements 1916a, p. 121).
association so defined and perceived would be of immense size, considerable
environmental heterogeneity (as noted earlier), and of a mosaic
pattern among other associations of the same formation. Warming (1909,
p. 145) specified: “Associations may occur irregularly as patches
in the formation; or may exhibit a zonal arrangement”. Tansley (1926,
p. 31) stated it thusly: “Associations are, on the whole, large units,
with wide extension, though this may be, and practically always is,
interrupted by the occurrence of other associations”. Daubenmire (1952,
p. 302) described this same pattern when he identified associations
in coniferous forests.
that Warming, Tansley, and Clements shared a similar interpretation
of association. For example, all used the example of “reed swamp”
which was a community dominated by Phragmites
communis, Scirpus lacustris
or S.validus, and Typa spp. Though Warming (1909, p. 145) referred to “reed-formation”
he used these individual species as examples of associations within
that formation which would thus be consociations in Clementsian terms.
Tansley (1926, p. 31) referred to the “reed swamp association” but
did not specify single species units (= consociations) as a form of
association. Clements (1936, p. 264, 278) noted that “reed swamp”
was “the universal example” of a “serclimax” and Weaver and Clements
(1938, ps. 62-63, 100) treated the “reed swamp stage” as a seral stage
and not climax so that each unit of vegetation dominated by a single
one of these “reed swamp” species was a consocies, the seral equivalent
of the climax consociation.
difference between association vs. associes (or consociation vs. consocies)
between Tansley and Clements was the difference between Clements’
monoclimax (where meso-, mesic,
level would theoretically be the terminal regional climax) and Tansley’s
polyclimax (where hydric-, mesic-, xeric-levels could all lead to
local, say, edaphic climaxes). The important point is that all of
these ecologists of the English Tradition saw associations (associes)
at the same spatial scale. Since then a younger “descendent” of the
Anglo-American school cited this same example of a consocies (Polunin,
1960, p. 334, 505). Likewise, Polunin (1960, p. 333-335) gave the
classic Clementsian units of vegetation verbatim from Clements (1936)
climax paper illustrating the vast profusion of the Clementsian view
of vegetation and its dynamic development and the persistence of the
Anglo-American Tradition of Vegetation Science.
Critical note: the important sweeping— and inevitable— conclusion is not that one ecologist or school (= tradition) was “right” or “more nearly correct” and some other school or model was “wrong” but rather which one(s) formed the basis and had most impact on current applied ecological thought. The fact is that the paradigm (some would say “philosophy”) of the Clements-Tansley group going clear back to Warming and Grisbach was the view that dominated American, British, Canadian, and South African ecological thought. And this domination— almost an exclusion of counter thought— was profoundly influential on the fledging disciplines and professions dealing with management of native vegetation and, for that matter, natural resources in general (eg. Soil Science, Wildlife Management).
current systems treating of range and forest vegetation, students
of these resources must understand the basis of this Vegetation Science
upon which Range Management and Forestry are built. That basis is
types (both rangeland and forest cover types) are one of the best
examples of this lasting Clementsian influence. As with range site,
there is no specific level or unit of vegetation in any classification
or vegetation mapping system that corresponds exactly and consistently
to range type (rangeland and forest cover type). It was shown previously
in this review that range site is a unit of vegetation and certain
environmental or habitat factors, especially soil (Range Site section).
By definition, range site cannot be “retrofitted” into any system
or classification scheme that is devoted solely to vegetation and
that ignores habitat. By contrast, both plant formation (climax vegetation
at regional or zonal scale) and plant association (the Anglo-American
association at any and all scales) are both units strictly, solely,
of vegetation with no environmental factors (except the biotic interactions
of the vegetation) directly included. As explained earlier, this is
the exact situation with the Daubenmire habitat type which is the
equivalent of the Daubenmire
association. Vegetation cover types are also strictly, exclusively,
units of vegetation and therefore could theoretically match exactly
one or more units of vegetation in the numerous schemes or hierarchies
of vegetation classification, description, or mapping. At present
none do match. Range cover types do not correspond directly and equivalently
to any unit of vegetation in existing vegetation classification systems.
For example, The Nature Conservancy unit of alliance in the USNVC
System corresponds but approximately to the SAF forest cover types.
do rangeland and forest cover types fit into vegetation classification?
To which—if any— units of vegetation do they correspond? From which—
if any —did they arise?
again it was the genius of Whittaker (1975) to synthesize and clarify
the various uses of concepts in context of vegetation types or cover
types and to suggest the origin of forest and range types. In making
more sense than most out of plant community classification Whittaker
(1975, p. 128, 135) stated that the biome or formation is a major
kind of community classified or defined, in principle, solely by physiognomy
but, in practice, a combination of physiognomy and environment is
required. “The physiognomic approach classifies communities by structure—generally
by the dominant growth-form or the uppermost stratum or the stratum
of highest coverage in the community”. Further:
or physiognomic classification is the usual approach to description
of the communities of a continent, or of the world, and it is widely
used by geographers, climatologists, and soil scientists as well as
ecologists” (Whittaker, 1975, p. 128).
with the preceding discussion, Whittaker (1975, p. 135) explained
that “on a given continent” biome (or formation) is the broadest possible
classification level or structural/organizational unit of plant and
animal community (or of plant community, vegetation, only). He then
went one unit of scale larger and one
organization level of community higher to define biome-type
or formation-type as “[t]he still broader [thus the broadest
of all] grouping of convergent biomes or formations of different continents”.
Obviously the biome-type or formation-type is the broadest unit or most general kind of vegetation (eg. “grassland biome type” and “desert biome type” include all grasslands and deserts on Earth). This is not to be confused with vegetation or cover type which is the major subdivision of biome or formation. But the use of the term “type” at different levels of organization and scale for the grouping of several units at these respective levels is consistent. Type is the all-inclusive word for the unit that encompasses all forms or kinds of plants and animals or of vegetation at a given taxonomic level (taxon) of organization.
|Cover Types are Dominance Types|
|Top of page|
(1975, p. 128) followed the biome and formation unit with the unit
he labeled as dominance-type:
by dominant species is a natural and widely used approach.
Community-types defined by their dominant species can be termed
dominance-types, but often they are called simply ‘types’”.
noted that plant communities are usually dominated by more than one
species “and subjective decisions on what combinations of major species
ought to be recognized as dominance types are necessary to make the
classification work”. The subjectivity (and considerable experience
and familiarity with the vegetation involved) notwithstanding,
dominance types are “quite workable … and physiognomy and dominance
can be used together, with dominance-types subordinate units within
last phrase Whittaker described the typical arrangement or organizational
pattern of the major units of vegetation as commonly used by foresters
and rangemen, at least in North America. Whittaker (1975, p. 128-129)
pointed out that ecologists like Clements and Braun used “as units
very broadly defined dominance-types, or groups of dominance-types”.
Their term for these broad dominance-types was, of course, the association
as defined by dominant species or genera such as the oak-hickory,
beech-maple, maple-basswood, and oak pine associations or, as they
are synonymously known, “types”. This usage was also noted by Shimwell
(1971, p. 62). In other words, type is often at the association
level as the largest or broadest unit or subdivision of a given formation
(eg. the preceding associations within the deciduous forest formation
of eastern North America). This is the exact usage or organization
(community hierarchy) of Braun (1950, p. 10-11). As quoted previously,
association was explained in considerable detail in Plant Ecology
(Weaver and Clements, 1938, p. 478-482) after having first defined
association on pages 93-94:
climax formation consists of two or more major subdivisions known
as associations. These are
climax communities associated regionally to constitute the formation.
The number of associations in a particular formation is naturally
determined by the number of subclimates within the general climate
of the formation. Each association is marked by one or more dominants
peculiar to it…An association is similar throughout its extent in
physiognomy or outward appearance, in its ecological structure, and
in general floristic composition [the mixed-prairie association was
one example used; likewise Stipa
spartea and Sporobolus heterolepis
were two dominants of the true prairie association]”.
was requoted at extended length to show the key roles of physiognomy
and floristic compostion which Clements retained from the association
of Warming (1909, p. 145).
visible unity of the climax is due primarily to the dominants or controlling
species. All of these belong to the same life form. … Each formation
is named after two of its most widely spread and important dominants”
(Weaver and Clements, 1938, p. 91).
A concise summary by Shimwell (1971, p. 53) explained this arrangement and the entire Clementsian hierarchial organization (complete with seral units and climax units mentioned above):
were subdivided into associations
which could be characterized by their codominant species. Within the
association, if a single species was the physiographic dominant then
the term consociation was used, while these were further subdivided into societies
each characterized by subordinate species.
However, these terms were restricted to the considered climax
vegetation type. All
other developmental units leading up to a climax, all seral stages,
were given parallel terms such as associes,
consocies and socies”.
this passage it is the association that is the vegetation unit relevant
to the current discussion. The Clementsian association (or consociation
where there was a sole dominant) was the unit of the “climax vegetation
type” which was determined by dominant or co-dominant species. This
description showed that vegetation type corresponded to association
which was defined or identified by its physiographic dominant(s).
Ergo, the unit Whittaker (1975, p. 128) identified as dominance-type.
(1975, p.129) was careful to specify that “the American association
of Clements and Braun” was distinct from the floristic association
of Josias Braun-Blanquet or the Zurich-Montpellier School of Phytosocioloy
(= Releve Method). Shimwell (1971, ps. 57, 59) drew the same distinction.
Use of the terms association and alliance for the lowest
and second lowest units of vegetation in The Nature Conservancy USNVC
System followed in similar format the hierarchy of the Braun-Blanquet
Zurich-Montpellier (Shimwell, 1971, ps. 56-62).
association in the USNVC System is the Braun-Blanquet association
and not the American association which Clements adopted from Warming.
It is the Warming-Clements association (often subunits thereof) that
is the basis of the cover or dominance types of range and forestry
Nature Conservancy United States National Vegetation Classification
System is primarily an application of the Zurich-Montpellier Tradition
(elaborated by Shimwell, 1971, ps. 45-47, 50-53, 56-62) to the vegetation
of North America (specifically the United States of America).The USNVCS
is largely an adaptation of the Ellenberg and Mueller-Dombois (UNESCO)
classification from which the former is modified at upper levels (Grossman
et al., 1998, p. 20). It follows that the SRM and SAF cover types,
which are essentially dominance-types derived primarily from the Anglo-American
Tradition of Clements and Tansley (Shimwell, 1971, ps. 45-62 passim),
will inherently correspond poorly to the The Nature Conservancy System.
This was bound to be the case because the SAF/SRM cover types and
The Nature Conservancy USNVCS alliances are units derived from vegetation
classification systems of two schools or traditions of plant community
ecology that have been distinct and separate for 90 to 100 years (again,
Shimwell ). This was shown even before The Nature Conservancy
USNVC System was developed when (as discussed above) the Ecological
Society of America Vegetation Classification Panel (1997) in its initial
report rated, as a level or unit of vegetation, the SRM cover type
rating was understandable given that vegetation units are from two
distinct traditions. TNC and ECA rated cover type relative to their
tradition and found it to be
unacceptable or least acceptable. SAF and SRM with their units
derived from another tradition should— for purposes of clarity and
consistency— reciprocate toward the USNVC System and rate the USNVCS
association and alliance at the bottom of their lists.
review of its initial report (ie. its second report) on an initiative
for a classification of United States vegetation the Ecological Society
of America Vegetation Classification Panel (1999, p. 11-12) concluded
that the SAF and SRM cover types and dominance types were
close approximations of each other: dominance types “are very
similar in concept to ‘cover types’ for simple, efficient inventory
and mapping purposes”. Community-layer dominance types “are
simply a convenient, descriptive subdivision of Cover Types or Domanance
Types based on the dominant species in a lower, conspicuous layer
of vegetation”. In this second report the ESA Vegetation Classification
Panel did not relate or equate cover or dominance types to any units
of vegetation in The Nature Conservancy USNVC System. The Vegetation
Classification Panel did discuss briefly the unit of plant association,
but only from the standpoint of “[t]he two major association classification
approaches in North America that are based predominantly on composition
of the entire plant community” which are the 1) Braun-Blanquet and
2) Daubenmire systems. Specification of “entire plant community” automatically
eliminated any of the systems based on dominance (distinction based
on dominant species) such as that of Weaver and Clements (1929, 1938).
Yet these dominance-based systems are the systems or classifications
which have dominated vegetation schemes and hierarchies used almost
exclusively in Range Management and Forestry in North America. In
the USNVC System both cover and dominance types were disregarded or
ignored as was plant association as defined and designated by the
Anglo-American Tradition (ie.the association as developed over the
words, The Nature Conservancy USNVC System made no use of any of the
units of forest and range vegetation traditionally used by American
workers except that of the habitat type as defined by Daubenmire which
includes all layers of vegetation and not just the layer of dominants.
Furthermore, given that “the USNVC is of existing, not potential,
vegetation” (Ecological Society of America Vegetation Classification
Panel, 1999, ps. 8, 14) even the Daubenmire association and habitat
type was irrelevant for the USNVC System because the Daubenmire association
is a “type of climax phytocoenosis” and “based on samples restricted
to ‘near-climax’ vegetation” [ie. potential natural vegetation] (Ecological
Society of America Vegetation Classification Panel, 1999, p. 12).
Thus, the USNVC System is a modification of and based on the Braun-Blanquet
releve phytosociological system (the Zuric-Montpellier Tradition or
School of Phytosociology) of continental Europe and in final effect
totally ignored the entire heritage of American research on classification
and description of range and forest vegetation. As asserted by the
Ecological Society of America Vegetation Classification Panel (1999,
p. 13), a partial exception to the preceding fact were studies of
vegetation “sampled with releves from late successional stands …”.
Yet, examination of the investigations cited by the panel revealed
that this sampling too was related back to “potential climax vegetation”.
The USNVC System also differs from such vegetation maps as those by
Kuchler which are of potential natural vegetation and not existing
doubt or debate, the United States National Vegetation Classification
System is a system separate from such units as range cover types and
the Anglo-American unit of plant association on which range and forest
cover types are based. “Classification of existing vegetation and
classification of potential natural vegetation are complimentary and
of equal importance in synecology” (Ecological Society of America
Vegetation Classification Panel, 1999, p. 14).
So said and homage given to classification systems for climax
vegetation, the obvious fact is that they are two separate though
above, both the SAF and SRM cover types are of “existing vegetation”,
but also as noted previously most of the rangeland cover types described
are, upon close reading, closer to climax or potential natural vegetation
than to seral communities (any disclaimer-like statements made by
Shiflet [1994, p. xii]
notwithstanding). By way of example, compare how many rangeland cover
type names begin with and list as dominants “Bluebunch Wheatgrass”
or “Idaho Fescue” versus how many begin with or list as the dominant
species “Cheatgrass”. Point made. Likewise, certain SAF forest cover
types are climax types and correspond closely to potential natural
vegetation such as that mapped by Kuchler (Eyre, 1980, p. 3).
Undoubtedly some of the USNVC units will be of climax vegetation,
but this new classification scheme offers little to Range Management
professionals that is not in existing range literature.
Conclusion: the unit(s) or level(s) of vegetation traditionally used in North America that most closely correspond to cover (= dominance= vegetation= grazing= range) type as applied in Forestry and Range Management is the association or, its seral counterpart, the associes. Cover type and association remain the basic descriptive units of vegetation intermediate between biome or formation and range site. These hierarchial levels are still in use and of great value because much of the most important and detailed reports of range and forest vegetation used these units and these studies remain cornerstones of Range and Forest Ecology.
|Origin of the term 'Type'|
|Top of page|
actual connection of the forest and range types to the Clementsian
association (or the seral unit associes in cases where the forest
or range vegetation is seral not climax) is obscure and seems not
to have been documented other than indirectly. Neither Eyre (1980)
nor Shiflet (1994) included even a brief review of the type concept.
and Korstian (1947, ps. 356-397) and Baker (1950, ps. 22-47) reviewed
units and systems of forest vegetation at a time when such approaches
were as utilitarian as they were academic and when the history of
their development was fresh in the “collective mind” of Forestry.
These silviculturalists discussed such forests or forest vegetation
units as the various kinds of formations (eg. climatic vs. physiognomic),
forest regions or forest vegetational areas, associations, and forest
types. There were different kinds of all units and hierarchial levels
depending on purpose and author or mapper even at this relatively
early stage or mid-age of American Forestry literature. (The American
Society of Range Management was just “germinating”.) Both Toumey and
Korstian (1947) and Baker (1950) distinguished forest cover type from
the other kinds of forest types: 1) management, 2) permanent, 3) temporary,
4) physical, and 5) indicator. It is interesting from a historical
perspective that then, as now, forest cover type was of the present
vegetation (could be seral or climax) and had the current meaning
(Toumey and Korstian, 1947, ps. 382-383; Baker, 1950, ps. 34-35; Munns,
1950, p. 88). At this time the Society of American Foresters (Baker,
1945) and Eyre (1954) published its revised
descriptions of forest cover types in North America, a project
begun in 1929 (Eyre, 1980, p. v).
to Clements (1920, p. 337) and Toumey and Korstian (1947, p. 379 in
a portion that is essentially the review from Clements ) the
term forest type was used first by Graves (1899) of the United
States Department of Agriculture Division of Forestry to mean a dominance
(= cover) type of natural forest vegetation. Baker (1950, ps. 31-33)
determined that the Society of American Foresters decided upon this
concept for forest cover types at a special symposium (Dana et al.,
1913) in the beginning days of their profession.
though the current concept and usage of forest cover type was established
at the onset of Forestry and Forest Science in North America and while
this coincided with the dawn of Ecology and the emergence of Clementsian
Ecology (compare 1913 to the publication of Clements’ Plant Succession
and Plant Indicators in 1916 and 1920), cover type was not
an ecological unit or an equivalent to any ecological unit. Toumey
and Korstian (1947, ps. 383-384) wrote:
type, as at present recognized and based on floristics and economics,
has no equivalent in ecology. It takes no account of site factors,
consequently temporary and permanent forest communities with unlike
site factors may fall into the same cover types so long as the dominant
species are the same”.
recall that cover types are based on present vegetation and
not necessarily on climax or potential natural vegetation. In contrast,
permanent forest type is the equivalent of climax forest vegetation
so its synonym is climax type (Toumey and Korstian, 1947, ps. 380-384;
Baker, 1950, ps. 44-46). Forest cover type can include both permanent
and temporary forest types. Examples of the latter include subclimax
forest types or ecologically transitional forest types like those
of Pinus strobus of the
Great Lakes forest region and Pseudotsuga menziesii of the Pacific Northwest Coastal forests. Thus
even where species like eastern white pine and Douglas fir are clearly
seral to the climax forest vegetation they are regarded as forest
cover types because they are so valuable economically even though
they are, when classified as to ecological forest type, temporary
forest types and not permanent (= climax) forest types.
it was through the correspondence or equivalence of permanent (= climax)
forest types to the Clementsian associations (and temporary [= subclimax]
forest types to the Clementsian associes) that eventually led to the
close approximation for forest cover types to a generic, nonspecific,
“more-or-less” Clementsian association with both terms used in less
restrictive, less precise meanings than originally intended (Toumey
and Korstian, 1947, ps. 382-384; Baker, 1950, ps. 44-46). Both of
these Silviculture textbooks noted that the term association had different
meanings to different ecologists or foresters (Toumey and Korstian,
1947, p. 377; Baker, 1950, p. 44). “Forest types as conceived by one
writer are not the same as those of another” (Toumey and Korstian,
1947, p. 379).
and Korstian (1947, p. 382) noted that there appeared “wide divergence
in opinion as to what constitutes a forest type”, but they interpreted
Clements (1920) in Plant Indicators as having concluded “that
the classification of forest into associations by ecologists and into
forest types by foresters differs more in emphasis than in fact” (Toumey
and Korstian, 1947, p. 382). Technically Clements did not relate or
equate associations to forest types. The section of Plant Indicators
referred to and interpreted by Toumey and Korstian (1947) was entitled
“Forest Types” (ps. 337-345) and when Clements (p. 342) wrote “… they
differ more in emphasis than in fact” he referred to the first part
of that same sentence which was “… of the opinions just summarized”.
These were opinions of numerous foresters all discussing various versions
of forest types including cover, management, permanent, temporary,
physical types. There was no reference whatsoever to associations.
However, a sizable portion of Plant Indicators (ps. 105-235)
was devoted to description of actual (not abstract) vegetation and
this was organized on the basis of formations and associations. Most
importantly, both Toumey and Korstian (1947) and Baker (1950) concluded
that the plant association as defined or interpreted in the Clementsian
concept (including being the main subdivision of the formation) was
the rough equivalent and theoretical basis of forest cover types.
This seems to have been a widespread perception during the formative
years of the Clementsian concept of association and the invention
and adoption of vegetation cover type. This is indicated by the fact
that forest cover type corresponded to plant association in the common
textbooks of the day.
“indicator” that vegetation types as used in America corresponded
to Clementsian units of vegetation is to be found in the “Grazing
Types” subsection of the “Grazing Indicators” section of Plant
Indicators (Clements, 1920, ps. 270-283). Clements grew up on
the central continental grasslands when virgin sod was still widespread
and he was educated at the great prairie land-grant University of
Nebraska which became the nucleus of the “founding school of American
plant ecology” (Tobey, 1981). As such Clements was much more a rangeman
than a forester. Predictably he dealt with grasslands in more detail
than forests. (This was also the case in Bio-Ecology co-authored
with Shelford from the adjoining prairie state and land grant University
of Illinois.) In Plant Indicators Clements did relate grazing
types to formations and associations in the portion that preceded
forest types. It is logical that foresters like Baker, Korstian, and
Toumey drew conclusions from the preceding and more detailed section
and applied it to forest types. Thus while Clements did not relate
forest types to associations and formations, foresters could have
made this rational adjustment as a logical and consistent extension
of Clements’ more comprehensive treatment of grazing types.
obvious from the “Grazing Types” portion of Plant Indicators
that Clements’ grazing types were of different scales and that his
grazing types corresponded to both formations and associations (Clements,
1920, ps. 273-275) as well as at the smaller scale (s) of
“local grazing types” or “practical grazing types”.
This was written so as to leave no doubt:
grazing types.--While the main grazing types, such as the formation
and association, indicate the comparative value of great regions,
as well as the groupings possible in any one, it is the local groupings
which determine the carrying capacity of a particular ranch and the
proper system of management to be employed upon it. For this reason,
they may well be termed practical grazing types. In areas relatively
uniform, a single grazing type composed of the two or three major
dominants of the association may cover a wide extent.”
Clements ended this portion discussing the faciation and the facies, the subunits of the association and the associes or consociation and consocies, respectively. It is clear that Clements used grazing types as he did vegetation types in a generic, multi-level/multi-unit sense. The careful reader can also detect in the local grazing types the forerunner or germ of the smallest unit or kind of range, the range site. Clements was always ahead of his time and his influence can be found in almost all major concepts dealing with units and analysis of range and forest vegetation.
|Historical Note: "Founding Fathers" of Range Management|
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|[NOTE: Arthur W. Sampson is traditionally and deservedly regarded as the “Father of Range Management” based on 1) his early range research, including studies of vegetation and plant succession, (his investigations actually involved experiments that used grazing trials, reseeding, etc.), 2) his teaching of university courses in Range Management and Plant Ecology, and 3) authorship of what is usually thought of as the first actual textbook in the subject, Range and Pasture Management (1923, John Wiley & Sons). In 1919 James Jardine and Mark Anderson of the U.S. Forest Service wrote USDA Bulletin 790, Range Management on the National Forests, a 98-page professional paper that became known as the “bible” of Range Management (Wasser, 1977) and that is often regarded as the first full-fledged “book” on the subject. This “range bible” came 20 years after Jared Smith (1899) authored the 47 page, pamphlet-size USDA Bulletin 16, Grazing Problems in the Southwest and How To Meet Them. Bulletin 16 was arguably the first Range Management manual though it was more of a report, with recommendations on range deterioration in Texas and New Mexico.The previous year two publications (again, more in the nature of reports) on the problems of range depletion in Texas had been authored by Bentley (1898a, 1898b). It was in 1899 that H.C. Cowles published his pioneering— no pun intended— study of plant succession on lake sand dunes from which Clements (1916a) took his model of vegetation development published in Plant Succession. It could be argued that neither Sampson (1923) nor Jardine and Anderson (1919) wrote the first textbook, but that it was Will C. Barnes (Inspector of Grazing, U.S. Forest Service) who wrote the first textbook and range “bible” in his Western Grazing Grounds and Forest Ranges published by The Breeder’s Gazette in 1913. Wasser (1977) stated that Barnes (1913) was “the earliest semitechnical book about Range Management”. Western Grazing Grounds placed a decidedly heavy emphasis on range livestock management and production (including poisonous plants, livestock diseases, and livestock predators) and laid relatively less importance on the range itself. Yet, it began with range plants (including photographs and line drawings) and was a text and reference for range magnagers and operators. Sampson’s Range and Pasture Management followed closely the format used by Barnes including devoting three out of 29 chapters to poisonous plants. In Livestock Husbandry on Range and Pasture, Sampson (1928, also John Wiley & Sons) followed more closely Barnes’ format including chapters on livestock diseases and depradation. Barnes (1926) followed Grazing Grounds with The Story of the Range, a 59 page (but small print) USDA publication, that dealt more with range use in a historical context and featured public range policy, including the “keen but friendly rivalry” between the US Departments of Agriculture and Interior.|
|All these titles indicated
that they dealt with range, grazing, pasture, or livestock and that
they were practical and industry oriented in their contents. Of these
early range authors only Sampson took management of range beyond practice,
craft, husbandry, policy, history, etc. to put the nascent profession
of Range Management on a scientific basis. “Sammy” had a Ph.D., was
a range researcher, and became a university professor early in his career.
He was the scientist, an ecologist, and contributed concepts and theories
as well as practices to the emerging discipline of Range Science (ie.
as a rangeman, Sampson was range scientist as well as range manager).
In this period when Range
Management was emerging as a profession built on the infant discipline
of Range Science, Frederic Clements was most active as an author.
Like Sampson, Clements was an ecologist and a researcher (an “escaped
professor” as he dubbed himself). Clements and Sampson had nearly
identical, as it were, backgrounds and academic “pedigrees”. Both
men were born in Nebraska (Clements 10 years earlier) and both were
products of the Botany program directed by Dr. Charles E. Bessey at
the University of Nebraska. Clements received his Ph. D. from Nebraska
in 1898; Sampson earned his MS from Nebraska in 1907 and his Ph. D.
from Johns Hopkins and George Washington University in 1917 (Tobey,
1981, ps. 238-239; Casamajor, 1965, p.115).
As an author of ecological
monographs and scientific papers for prestigious journals Clements’
titles did not readily emulate the land grant ideal of “practical
education” (from the Morrill Act) or an industry orientation. Such
appearance was misleading. For all of Clements’ elaborate, sweeping
concepts and classification of vegetation, he always sought to apply
theory to on-the-ground practice. “It is believed that succession
and indicators constitute the most essential and useful form into
which the results of research can be put for practical use” (Clements,
1920, p. iii). Clements (1920) wrote Plant Indicators- The Relation
of Plant Communities to Process and Practice, his second monumental
monograph as “a companion volume to ‘Plant Succession’”, aimed at
application of the science of Plant Ecology to the arts of farming,
lumbering, and range-based ranching. The “indicator concept” was application
of the ecological viewpoint that species of plants (and formations,
associations, consociations, primary seres, and secondary seres) indicated
certain conditions of climate, soil, etc. as well as human modifications
such that there were “agricultural indicators”, “forest indicators”,
and “grazing indicators”. In Plant Indicators, for example,
is to be found the genesis of the Dyksterhuis (1949) categories of
decreasers, increasers, and invaders in the concept of seral types
as grazing indicators:
“In the grassland climax, where the effects of overgrazing have been most studied, it is possible to recognize three or four stages. The first is marked by the decrease or disappearance of Stipa or Agropyron, or of both of them, and the corresponding increase of the short-grasses wherever these are associated; the second stage is characterized by the greater vigor and abundance of the normal societies, as well as by the increased importance of some; the third stage begins with the replacement of the grasses by annuals, while the fourth is marked by the spread of annuals and of introduced weeds generally over the area….These four stages indicate so many primary degrees of overgrazing, while minor degrees are denoted by the dropping out of particular dominants or subdominants…. Palatability is the chief factor in determining the sucessive disappearance of species, and hence the indicators of the corresponding degrees of overgrazing, though the sequence is often disturbed by the vigor of certain dominants. Since there are few species that are wholly unpalatable or inedible, it becomes possible to construct for a particular community a complete sequence of indicators, reflecting each appreciable degree in the process of overgrazing” (p. 298). [Note here even the importance of “vigor” as a factor in considering the ecological status of plant communities.]
Clements (1920, ps. 298-308)
then followed this with discussions of changes in range plant communities
with overgrazing and lists of species indicating degrees of overgrazing
(departure from climax). He discussed subshrubs, cacti, shrubs, and
annuals as indicators (eg. “Annuals are typically indicators of serious
disturbance, and hence serve to mark the existence of serious overgrazing
when abundant. They are the universal pioneers of secondary succession.”
[Clements, 1920, p. 301]).
Section VI. (Grazing Indicators)
of Plant Indicators (ps. 270-335) was a mini-textbook in Range
Management. It included subsections on “proper stocking”, “range improvement”,
“eradication of brush”, “water development” “rotation grazing”, “herd
management”, and even a line diagram showing arrangement of corrals
and sheds. This section is as much a manual or “bible” on Range Management
as was Jardine and Anderson (1919) or Barnes (1913), but it was within
a massive scientific volume of Plant Ecology or what could most precisely
be termed Vegetation Science.
Like Sampson, Clements combined science with practice to form the framework of practical science-based professional Range Management. With this combination, these two proto-type range scientists stood out as unique among their contemporary authors and range brethren. They were the founders of Range Management as an applied science as well as an agricultural art. This was largely through teaching and textbook writing in the case of Sampson and publication of strictly structured vegetation theories by Clements. In latter years Sampson published some work in demanding journals like Plant Physiology, but he primarily produced publications for the California Agricultural Experiment Station and Extension Service (Casamajor, 1965, 115-116). Textbooks by Sampson bespoke their applied orientation and were written for undergraduate students and the better educated stockmen, lumbermen, forest rangers, etc. of the day. Clements’ tomes had high-sounding formal titles and appeared as if written for other scientists and specialists (they could be read by Sammy’s crowd but less easily). Even the personal lives and personalities of these two prominent ecologists were different. Sampson had a great sense of humor, loved sports, and generally enjoyed being around people (Casamajor, 1965; Parker et al., 1967). According to Clements’ close friend, Arthur Tansley (1947), Clements was kind and considerate but apparently all-business so to speak. “He was decidedly puritan, even ascetic” and while able to laugh at himself “his manner was apt to be tinged with a certain arrogance”.
It was to be expected that of the two men most responsible for scientific development of Range Managaement, Sampson would be the one most associated in the public mind with creation of this new agricultural field and the increasing appreciation of range as an important renewable natural resource.
The appearance of almost all of the major seminal works on Range Management within such a brief period is of historical importance. Although Forestry had a somewhat earlier beginning than Range Managaement in North America and the latter grew out of the former, Range Management was always a “red-haired stepchild” to the “board foot timber beasts”. Even though grazing feees on National Forests were a sizable portion of revenue generated from the Forests, “grazing” was not accorded much respect or consideration. By way of evidence, even the immortal Gifford Pinchot (1903) in his famous two part A Primer of Forestry, Bulletin 24, devoted but seven pages out of a total of 177 to “grazing”, “trampling” and “browsing” with the discussion on ways “in which grazing animals injure the forest”. (This outlook by foresters has not changed much in the ensuing 97 years.) Thus, the chronology of Jardine and Anderson (1919), Clements (1920), and Sampson (1923), the first three major works dealing with actual management of range, was of paramount importance.
While the range livestock
industry and some management of ranges— to the extent of moving animals—
traces to antiquity (Genesis 13: 1-12 recorded a range war everted
between Abraham and Lot), the beginning of management of native grazing
land as something besides an activity traces to a relatively small
cadre of men. The historical review by Wasser (1977) is probably the
best discussion of the development of Range Management as a profession
(“technical Range Management” was Wasser’s usage). C.C. Georgeson,
H.L. Bentley, and Jared G. Smith
(all associated with the Texas range problem) and Will Barnes
(and probably a few non-publishing contemporaries) with the “core”of
Jardine, Anderson, Clements, and Sampson constitute the “founding
fathers of Range Management”. Although all these men brought the best
existing knowledge to an embryonic profession
(eg. Georgeson was a professor) Sampson and Clements provided
the most obvious leadership in the application of science (scientific
theory and experimentation)
to husbandry of natural pasture.
Sampson was propelled to prominence as “Father of Range Management” as a result of the combination of: 1) his set of three textbooks published by 1928, 2) some of the earliest experimental range research reported beginning in 1913, 3) continuous teaching of Range Management courses in a prominent university school of Forestry, and 4) sustained research output on both practical and theoretical subjects. This is well-known. What is not as well-known (at least not “well-remembered”), and what has been overlooked by many workers, is that Frederic Clements would logically be “first runner-up” for the distinction rightly held by Sampson.
The combination of easily read textbooks and university teaching along with experimental research put Sampson, to use a cliché, “in a league by himself”. The “founding father” most similar to Sampson was Clements. In fact, it was Clements as Sampson’s senior and the main member of the “founding school” at Nebraska who served as Sampson’s teacher in most matters ecological. This is obvious in Range and Pasture Management (Sampson, 1923) which followed closely in content and organization a combination of Western Grazing Grounds (Barnes, 1913) and Section VI. of Plant Indicators (Clements, 1920). For example, Sampson (1923, ps.107-119, 127-130) followed Clements’ indicator plants method and used as an illustration the four stages in depletion of Agropyron-Stipa climax grassland quoted above from Indicators (p. 298). Sampson (1923, p. 128-130) gave examples of species in these stages and at beginning of this part (p. 108) Sampson cited Plant Indicators (ps. 270-335: the entire Section VI). As remarked in the Introduction of this review, Sampson also included agronomic pastures in his 1923 text and portions pertaining to tame pasture did not trace to Clements. Sampson retained his reliance on Clementsian Ecology in his last textbook (Sampson, 1952) in which he drew heavily from Plant Ecology (Weaver and Clements, 1938). It was commonly known among his faculty colleagues that Sampson admired the work of Weaver and Clements (Casamajor, 1965, p. 116).
It is revealing that upon Sampson’s retirement, H.F. Heady (Ph.D, Nebraska and one of the most active range scientists in creation of the American Society of Range Management) was recuited and hired away from Texas Agricultural & Mechanical College. Heady remained a master of Clementsian theory and its application to Range Management, including grazing methods. Readers desiring an outstanding explanation of the basic Clementsian model, with appropriate inclusion of polyclimax and climax pattern views, can find none better than “Structure and Function of climax” (Heady, 1973). Application of the Clementsian model to Range Management and in context of contemporary issues (eg. climatic change) was also discussed in Heady and Child (1994, ps. 123-145).
In Plant Indicators (Grazing Indicators) Clements did not limit his consideration of Range Management strictly to ecological aspects. He not only had sections on livestock management but also included some tables of nutrient content (proximate analysis) of forage species (Clements, 1920, ps. 286-292). Clements realized the key function of range vegetation in providing feed for livestock and wildlife. Sampson was also aware of the central role that the field of Animal Nutrition had in the grazing industries and the emerging fields of grazing land management. This was shown in Sampson’s second textbook, Native American Forage Plants, which was “intended to be a companion volume to ‘Range and Pasture Management’” (Sampson, 1924, p. vii) and in which Chapter I was “Pasture Forage and Animal Nutrition”. In Clements’ abridged range textbook inside of Plant Indicators and in Sampson’s second textbook that was devoted to range forage and browse plants is evidence that both of these “founding fathers” anticipated the hybrid specialty of Range Animal Nutrition. Range Nutrition was an important part of range research in a “golden age” of grazing trials and animal diet studies before it shrunk in emphasis (C. Wayne Cook, personal communication) in the succeeding vulgar age of a “numbers game” of competititve grants, lowest publishable units, and an infatuation with research design for scientists over practical results and applications for stock raisers.
The direct contributions of Clements to Range Management and, secondly, to Forestry seem to have been lost from the collective mind and currently underestimated. These contributions were most likely overshadowed by Clements’ theories of plant succession, monoclimax, biome, and vegetation classification with its proliferation of terms. Apparently Clements is remembered as a theorist of vegetation and author of “big books on Plant Ecology” while his direct and equally lasting contributions to actual vegetation management were largely forgotten.
In the Organicism section of this paper the author challenged a conclusion reached by Tobey (1981) that Clementsian Ecology as a paradigm and the “founding school of American Plant Ecology” “failed”. The present writer concluded that the Tobey (1981, p. 8) claim of “breakup of the Clementsian microparagadigm” was incorrect because Tobey failed to appreciate the central role that Clements had in helping found the field of Range Management. Tobey (1981) failed to see that when the Clementsian paradigm moved from Grassland Ecology to Range Management it was not a paradigm shift but an expansion of applied Plant Ecology from primarily grassland to all range biomes and that it lead to Range Ecology with greater emphasis on grazing which led to the profession of Range Management. Also, but less importantly, the Clementsian paradigm moved into Forestry as for example in the monographic work by Braun (1950) on the eastern deciduous forests.
As discussed shortly, the appearance of Clements’ monographs, a vegetation classifiction system by Nichols, and development of the forest cover type concept coincided with appearance of books, agency manuals, reports, etc. in Range Management. This was clearly a phase in the developmental era of natural resource professions. Plant Indicators with its enclosed Range Management “textbook” was a major work in the development of Range Management and the recognition of range as a major natural resource the same as forests, soils, and wildlife. Plant Indicators was also influencial in settling on the vegetation unit of forest cover type as detailed above.]
|Role of Habitat|
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Range Site and Biome sections the point was made explicit that range
site, the most distinctive kind of range (the smallest taxon of natural
pasture) is a unit of habitat and not of vegetation per se. Each range
site is characterized by a unique plant community (a “one-of-a-kind”
vegetation) but this is due to or reflective of its causal habitat
which is typically defined more in terms of abiotic (edaphic, microclimatic,
etc.) than of biotic environmental factors. This does not deny the
obvious fact that organisms modify their physical-chemical environment
(the classic soil formation formula immediately comes to mind). Pioneer
ecologists were aware of the phenomena of organism-induced modifications
to their habitat. This was the basis of the Cowles-Clements “dynamic
vegetation”. Each stage of the plant community that developed along
a sere “improved” (modified to a more moderate, mesic, mature, etc.
degree) the seral habitat for the next seral stage of vegetation until
the habitat reached a dynamic equilibrium with the habitat-forming
factors which marked terminus of the sere, the climax. This was Clements
“vegetation development” and his term for that particular process
of plant succession that denoted “the collective effect of organisms
upon the habitat” was reaction (Weaver and Clements, 1938,
ps. 4-5, 234-238).
early ecologists recognized the role of habitat in development of
plant and animal communities and the reaction of organisms in modifying
habitat there was much debate in the seminal literature over what
emphasis should be placed on habitat in naming, classifying, and mapping
native vegetation. Eventually habitat came to have more importance,
at least prominence, at some levels or units of vegetation than at
others. Again, range site is basically a habitat unit delineated first
by abiotic factors (eg. soil, aspect, microclimate) and distinguished
secondly by unique vegetation. The larger community units such as
biome-type or formation-type, biome or formation, association, and—misleading
name notwithstanding— the Daubenmire habitat type are all defined,
named, mapped, etc. exclusively by the plant or plant and animal community.
Adoption of the ecosystem concept, foundation of the Tansley paradigm,
established the role of habitat for certain things in Ecology (eg.
community function) but not for others.What, if any, role habitat
should play in vegetation classification remains one of the most enduring
questions and persistent problems in Vegetation Science.
the relation of forest types to ecological units of forest vegetation
Toumey and Korstian (1947, ps. 383-384) noted that within a region,
the scale or area of a climatic forest formation (Toumey and Korstian,
1947, p. 374, 383-384), parallel series of associations formed due
to existence of parallel series of habitats. These series that form
habitats (which are equivalent to one another) constitute a common
habitat type. “Associations that are correlated with habitats which
form a habitat type” can be grouped into association types so that
“it is possible to group the many associations in a given plant formation
into a comparatively small number of association types” (Toumey and
Korstian, 1947, ps. 383-384). These authors drew this synopsis from
a paper by Nichols (1917) dealing with ecological classification of
again the close timing of the SAF cover type symposium, Clement’s
epic ecological monographs, and, now, the Nichols’ vegetation classification
paper. Nichols (1917) organized plant associations inside of association-types
where the latter were roughly the subdivisions of plant formations.
This suggested that association-types were the equivalent units, or
at least equivalent scale, of Clementsian associations. The relevant
point is: in an early vegetation classification system, units of vegetation
at the level or scale of association came to be equated to vegetation
is the perspective, the concept, that formations (later biomes) are
subdivided into forest vegetation types (ie. forest types as ecological
units are the foresters’ equivalent of associations and these forest
types are the major subdivisions or the most general units within
forest formations). It was explained earlier that Toumey and Korstian
(1947, p. 384) specified that forest cover type (and physical forest
type) had “no equivalent in ecology”. Therefore the equating of of
a permanent (= climax) forest type to forest association would not
automatically equate forest cover type to association. It was also
explained, however, that Clements (1920, p. 342) found these different
kinds of forest types to “differ more in emphasis than in fact”. As
such, the general equating of plant association to forest cover type
was a rational conclusion. Given that there was no such distinction
of different range types, but that range cover type “embodies both”
“cover type” and “vegetation type” (Shiflet, 1994, p. xi) the net
outcome was: Anglo-American plant association= forest and rangeland
cover types; range cover type corresponds, at least approximately,
to plant association.
sizes of plant associations also was an important feature. Clements
had previously equated grazing types as units of management to units
of vegetation at scales going down through the three largest or highest
levels of his vegetation hierarchy (the formation to association to
faciation, or the equivalent seral units). Size— scale (size of one
unit of vegetation or level of hierarchy in comparison to another)—
was (is) a point of confusion.
(and persistent) conceptual relationship among vegetation units is
that of habitat-type corresponding to a commensurate group of associations
identified as association-type (or, perhaps, association). This connection
can be traced back at least as far as Nichols (1917, ps. 309, 310)
to whom habitat-type was even “capable of algebraic expression” (Nichols,
1917, p. 317-318). To Nichols habitat-type was the habitat, the environment
and not the vegetation, but his habitat-type and association-types
usually corresponded to each other at the same level of organization
and classification. Nichols’ association-type apparently corresponded
to the formation of other ecologists (Nichols, 1923, p. 157). Therefore,
habitat-type was obviously much closer in spatial scale to the association
as defined by Clements and Tansley than to smaller units.
use of the term habitat-type and at the level of associations or groups
of associations took
place decades before synecologists
like Daubenmire reintroduced the term and repeated the equivalency
(at least rough correspondance) to the scale of association while
later redirecting the emphasis of habitat type away from environment
and making it a unit of vegetation or, most precisely, as the potential
area covered by an association. All this was done without referring
to or citing the work of Nichols. The term habitat type was not given
in SAF Forest Terminology, the then-current glossary of terms, (Munns,
1950). Nor could it be found in Baker (1950). Nichols (1917, 1923)
did not develop fully the habitat-type concept (and he certainly did
not use it as a unit of vegetation in his system of plant community
classification), but he did use the term and the concept at scale
of association, or association-type. Again, this was years before
Daubenmire (1952) first used it as a unit of land corresponding to
climax association and later (Daubenmire, 1968) as a vegetation unit
in his classification system. Still later, the U.S. Forest Service
adopted the Daubenmire version of habitat type and expanded it to
include actual habitat criteria (ie. returned the unit closer to that
of Nichols ). (The contributions— largely forgotten— of Nichols
were the subject of the next section.)
context of rangeland and forest cover types it is stressed again that
the habitat type of Daubenmire vegetation classification was at the
scale of association, the climax association and seral stages having
potential to reach that climax. In the original application of his
vegetation classification Daubenmire (1952) made little use of habitat
type instead using association as “the basic unit”. Daubenmire’s system
was covered above in the Range Site section where it was shown that
habitat type and association were the same size- or scale-wise (being
of the same land area). The pertinent point for the cover type unit
is what the Daubenmire plant association was (eg. what its size was)
relative to the association(s) of Clements, Tansley, Nichols, etc.
most vegetation units of the various systems this was not— probably
could not—be determined with precision (or accuracy). The area described
by Daubenmire (1952) in developing his system of vegetation classification
(which metamorphosed into the habitat type designation/description
method) had been described as seral to the “Thuja-Tsuga
association” in a previous vegetation study by John Weaver. (Like
his colleague Clements, Weaver seemed always to have "already
been there".) In Weaver and Clements (1938, ps. 481, 503-504)
this unit of coniferous forest in northern Idaho and adjacent parts
of neighboring states and Canada seemed most likely to have been in
the region of the “larch-pine forest: Lariax-Pinus association of the Thuja-Tsuga
Formation”. Daubenmire divided this unit into: 1) Pinus
ponderosa zone, 2) Pseudotsuga
taxifolia var. glauca
zone, 3) Thuja plicata-Tsuga heterophylla
zone, and 4) Picea engelmanni-Abies
lasiocarpa zone. Each of
these was divided into four associations except for 2) which had two
the Daubenmire associations were smaller than the traditional association
as interpreted by the Grisebach-Warming-Clements lineage (the English
Tradition). It seemed reasonable to characterize the Daubenmire association
as a subdivision of the Clementsian association. This is consistent
with Daubenmire’s adoption of the Tansley polyclimax instead of the
Clements monoclimax view and his recognition of edaphic and topographic
as well as climatic climaxes within the region. “Most of the associations
considered in the present study play different climax roles in different
parts of their areas, eg., climatic climax in one place, and topographic
climax in another” (Daubenmire, 1952, p. 303). This perspective and
inclusion of the understory species in association designations was
responsible for the smaller size of these Daubenmire associations.
association designations Daubenmire used scientific names of the one,
sometimes two, dominant species of the upperstory and the dominant
species of the understory (eg. Pinus
association”). This association nomenclature followed the format of
Clements (Weaver and Clements, 1938; Mueller-Dombois and Ellenberg,
1974, ps. 173, 175) except that Daubenmire included understory dominants.
four zones corresponded closely to the Clementsian consociation as
associations of Daubenmire (1952, ps. 306-319) were smaller, more
specific units than traditional forest cover types in having associations
differentiated within zones primarily on basis of dominant understory
species. Comparison of Daubenmire zones to current SAF cover types
revealed a reasonable degree of correspondence. Daubenmire (1952,
ps. 324-327 passim) discussed the fact that forest cover types typically
were based largely— usually exclusively— on tree species that dominated
the canopy. In the United States such cover types “show only the kinds
of commercially valuable species now dominating the land” (p. 324).
As these existing canopy dominants may not be climax or the potential
native vegetation, cover types mix seral with terminal vegetation.
This approach may omit the “benchmark” of the potential (= climax)
forest vegetation and create confusion when trying to base forest
management on objective criteria. Forest cover types are a form of
mapped inventory and when the current forest vegetation is eliminated
by disturbances cover types “have only historic value” (p. 324). Daubenmire
combined the dominant understory (the “subordinate union”, described
in the Range Site section) with the canopy dominant (the “dominant
union”) to represent the climax or potential forest vegetation throughout
the major layers of the forest. This served as a realistic guide to
scientific management. Inclusion of the understory was used to eliminate
some of the problems associated with forest cover types.
(1952, p. 325) explained the practical basis for his combination climax
association. For instance with regard to Range and Wildlife Management
classifying the land as to its forage productivity attention must
be directed at least as much to the subordinate unions of the forest
associations as to the trees” (Daubenmire, 1952, p. 325).
the climax plant association that somehow finally became the habitat
type of Daubenmire, and then the Forest Service, was a subdivision
of the traditional association and, as such, was a smaller, less heterogenous
unit. This resulted from dividing traditional associations into more
communities based on understory dominants. Daubenmire associations
were also smaller than forest cover types because the latter are based
only on dominant canopy trees. Overall, the associations of Daubenmire
were consistent in size with cover types when allowance was made for
division of these types into subtypes as distinguished by the greater
number of understory dominants (ie. area or size of community designated
only by upperstory dominants is greater or more zonal than size of
communities that are designated, differentiated, within the zonal
vegetation by inclusion of both understory dominants and the climax
canopy species). Also adoption of the polyclimax perspective and inclusion
of topoedaphic climaxes as well as climatic climaxes increased the
number of and decreased the size of Daubenmire’s climax associations
in comparison to the Clementsian associations. As such, the Daubenmire
habitat type corresponded more closely with size of the Tansley association
than with the association of Clements and Weaver.
given discrepancy between size of British and American associations,
the size relative to size of formations and the association as a community
concept remained consistent and compatable within the English Tradition.
The most obvious difference between the original Daubenmire (1952)
association (later to become habitat type) and
the vegetation cover types as they came to be applied by the
Anglo-American Tradition was
that associations were climax vegetation while cover types could be
either seral or climax communities.
(1968, ps. 259-263) described briefly his Landscape Hierarchy. This
is an ecosystem classification that, as was pointed out above, is
actually a vegetation hierarchy being based solely on vegetation.
It has four levels which lowest to highest are: 1) habitat type, 2)
vegetation zone, 3) vegetation province and 4) vegetation region.
examination of the use of habitat type by Daubenmire strongly suggest
that “his” habitat type-- which it will be recalled was the association
(Daubenmire, 1968, p. 32)-- was in spatial scale smaller yet roughly
similar to that of the Clementsian association. Daubenmire did not
state this, but he used “climax vegetation” at scale of “landscape
mosaic”. Daubenmire (1968, p. 29-30) stated: “ The term association
may be applied to any distinctive type of climax vegetation, whether
large or small, simple or complex. Some workers, however, consider
it desirable to recognize broadly defined associations, these being
subdivided into subassociations
or phases …”. He also noted: “Ordinarily one habitat type is highly discontinuous,
with intervening areas occupied by other habitat types differentiated
by either soil or microclimate” (Daubenmire, 1968, p. 260). Comparison
of this description to those of Warming and Tansley quoted above suggest
that the scale of the association (= habitat type) described by Daubenmire
was the same (or very similar) scale of Warming, Clements, and Tansley.
Daubenmire associations actually were smaller than the traditional
Clementsian association but that was not necessarily inconsistent
given that Daubenmire associations could be “large or small”. This
difference was again reflective of the adoption of polyclimax (vs.
monoclimac) perspective. Phases as subdivisions of associations determined
by soil or microclimate could be interpreted as the scale of range
site. In other words, associations are range cover types that are
subdivided into subassociations or phases which in turn correspond
to range sites.
his discussion of habitat type Daubenmire (1968, p. 261) used the
instance where “pure stands of Pinus
ponderosa that are climax always occur in environments that are
slightly drier than those in which Psudeotsuga
menziesii is a climax dominant” over a region stretching from
Canada to Mexico and Wyoming to California.
Throughout this interrupted, regional coniferous forest the
understory layer(s) vary greatly in species composition such that
Daubenmire (1968, p. 261) asked: “Should the P.
ponderosa stands in British Columbia be grouped with the wetter
Pseudotsuga forests there on the basis of close similarity of undergrowth,
rather than with P. ponderosa
stands in remote places where there are no undergrowth species in
common?” Daubenmire discussed both possibilities noting that the first
grouping “… would embrace a broad spectrum of variation in climate,
soil, and overstory dominants” while the second approach would result
in “recognition of all climax stands of P.
ponderosa as a basic group…” that is
determined by climate “… as a master factor…”. For purposes
of ascertaining the relative scale of the Daubenmire habitat type
(= association), the forgoing discussion clearly implied that the
association could be of a size determined by climate (ie. regional
or climatic climax) or, if the first alternative, each habitat type
(= association) would be of such size as to encompass a diversity
of climates, soil, etc. Either way, habitat
type fits the size description of the British-American association:
habitat type most closely corresponds to the range cover type and
not the range site. This is consistent with what appeared to be
the original usage of habitat type at the spatial scale and community
organization level of association-type, a supra-group of associations
that were described by the original definition as the subgroups of
a formation (Nichols, 1917, p. 309).
and Clements (1938, ps. 94, 481, 505) also used Pinus ponderosa and Pseudotsuga
menziesii as an example of an association in Rocky Mountain forests
where each species was a consociation (ie. a forest cover type or
range cover type). A difference between the traditional Clementsian
plant association and the Daubenmire habitat type (ie. originally
the Daubenmire  climax association) was that Daubenmire (1952,
1968) placed more emphasis on understory layers than did Weaver and
Clements (1938) who classified more simplistically on dominant species
of the upperstory. General usage by Weaver and Clements and Daubenmire
is consistent: habitat type = association = forest cover type (and,
in this case, also permanent [= climatic] forest type because both
associations were climax vegetation).
vegetation zone which was the next highest (next most general,
next largest) unit in his vegetation hierarchy, Daubenmire (1968,
p. 261) wrote: “All the area over which one association is climatic
climax represents a vegetation zone of essentially uniform macroclimate
insofar as vegetation is concerned”. This is not only Clementsian
regional (= climatic = zonal = mono-) climax but it is also consistent
with the climatic zone basis of Ecosystem Geography devised by Bailey
(1996, 1998) whose system, as noted above, is Clements and Tansley
down the line. Clements (1904, ps. 147-162) reviewed studies of vegetation
zones and traced recognition of vegetation zones back to the early
1700s. Bailey (1996, ps. 47- 49) discussed systems that mapped Earth
into ecological regions based on climate-vegetation zones and gave
much credit for development of this concept to the Russian soil scientist
V.V. Dokuchaev (1846-1903) who traditionally has been regarded as
the “Father of Pedology” (Joffe, 1949, ps. ix, 2, 8-9; Fanning and
Fanning, 1987, p. 3).
vegetation province was based on the “historic aspect of vegetation”,
the geologic flora or paleobotany, with a vegetation province including
those vegetation zones “which have had a somewhat common and distinctive
geologic history, which form a distinctive geographic unit at present,
and which exhibit strong threads of taxonomic homogeneity …” (Daubenmire,
1968, p. 262). Dominant species were the basis for “a common historic
background for a group of climatic climaxes”. This emphasis on climatic
climaxes over geologic time scale and inclusion of prehistoric flora
in evaluation of present vegetation was an original part of the Clementsian
model of dynamic vegetation that encompassed plant succession and
evolution over scale of geologic time (Clements, 1916a, ps. 279-422).
In fact, with reference to Plant Succession (Cooper, 1926,
p. 393) wrote: “The greatest contribution of all, however, is the
extension of the field of study to cover all time from the present
moment back to the very beginnings of vegetation upon our planet…
Clements was the first to organize the field of dynamic ecology as
a unified science covering the entire history of the plant population
of the earth”.
province is another echo of Frederic Clements. It is part of Clements’
phylogenetic system of seres as outlined in Plant Succession
(Clements, 1916a, ps. 183, 344-351). Daubenmire’s vegetation province
appeared to correspond to Clements’ clisere: “The clisere is the series
of climax formations or zones which follow each other in a particular
climatic region in consequence of a distinct change of climate” (Clements,
1916a, p. 347).
broadest (largest, most general) of Daubenmire’s vegetation hierarchy
is the vegetation region which is parallel to Baileys ecoregion
or macroecosystem, the equivalent of the biome plus its abiotic environment
as remarked previously. “The vegetation region as defined above differs
from the plant formation of Clements and certain others chiefly in
that a geographic area is emphasized, rather than a kind of vegetation”
(Daubenmire, 1968, p. 263). Clearly Daubernmire vegetation region
equals Bailey ecoregion and both equal essentially Clements’ biome
with its physical/chemical habitat (the Tansley ecosystem at scale
of Clements biome).
There appears to be some overlap of the Daubenmire units of vegetation zone and vegetation region with Bailey Ecosystem Geography units, and the vegetation province appeared to be as much a temporal unit as a spatial unit, but the closeness of units from these two systems is consistent with the Clementsian association and the SAF/SRM cover types that developed and correspond closely to the American concept of plant association and its subunit, the consociation.
|The “lost” legacy of George Nichols|
degree this ambiguity also existed in the ecological classification
system of plant communities proposed by Nichols (1923) when he used
the term association-type or, the full term, ecological
association-type (ps. 156-160). The association type was Nichols’
umbrella term that encompassed “all associations which resemble one
another in physiognomy and ecological structure, regardless of their
floristic composition”. To Nichols the association-type, like association
itself, was an abstract concept but the former was represented by
individual concrete associations. This was, however, problematical:
“Where to draw the line between the association, considered in the
abstract, and the association-type is a question which can no more
be answered dogmatically than the question of where to draw the corresponding
line between genus and species” (Nichols, 1923, p. 158).
In fact it was possible to apply the term association in the
abstract and the term association-type to the exact same unit of vegetation
at the regional scale (eg. beech-sugar maple of the deciduous forest
of eastern North America). Thus the tendency for individual concrete
associations to be referred to as association- types. Overall though,
abstract associations were the floristic subunits of the association-type:
“… an association-type commonly embraces several to many floristically
defined abstract associations”.
that the Clementsian association— a unit or level of vegetation in
the conceptual model that came to dominate, even define, Anglo-American
or English Tradition plant ecology— was both abstract and concrete
depending upon context, it is not clear if the association-type was
more or less synonymous with the predominate American interpretation
of association or if association-type was some unit intermediate between
formation or biome and Clementsian association. Nichols’ use of “reed
swamp type” (Nichols, 1923, p. 157) as an association-type clearly
placed it as synonymous with the association level or unit of Weaver
and Clements (1938), Tansley (1923), and Polunin (1960) as detailed
above. Nichols (1917, ps. 307, 318) previously made reference to “the
Likewise Nichols’ beech-sugar maple association-type was completely
synonymous with the maple-beech association of Weaver and Clements
(1938, ps. 481, 510-512). His oak-hickory association-type (Nichols,
1917, p. 310) was synonymous with the oak-hickory association of Weaver
and Clements (1938, ps. 481, 514-516). Conversely, Nichols’ xerophytic
conifer forest association-type was a larger, more general unit of
vegetation than the Clementsian association when the former encompassed
the Clementsian jack pine (Pinus banksiana) consocies (the seral equivalent of consociation,
hence a seral association) of the Canadian and Great Lakes forests
and the pitch pine (P. rigida)
type of the Atlantic (Nichols, 1923, ps. 156, 157; Weaver and Clements,
1938, ps. 481, 499). Also, Nichols (1923, p. 156) mentioned the “Chamaecyparis association of swamps” whereas Weaver and Clements (1938,
p. 497-498) observed that the white cedar (Chamaecyparis thyoides) was but a minor member of the lake forest
eastern white pine (Pinus strobus)-red
pine (P. resinosa)-eastern
hemlock (Tsuga canadensis)
(1923, p. 157) stated that the ecological association-type was identical
with the ecological forest-type, but he noted that foresters
made little use of the association. Ecological forest type was not
defined or even noted in any of the standard Forestry texts or any
of the Society of American Foresters term glossaries except the most
recent by Helms (1998) as ecological type defined as:
“ a category of land having a unique combination of potential natural (climax) community, soil, landscape features, climate, and differing from other ecological types in its capacity to produce vegetation and respond to management”.
sounded more similar to the definition/description of range or forest
site and indeed was listed by Helms (1998) as a synonym for habitat
type which, as discussed in detail above, the Society for Range Management
(Bedell, 1998) defined as “similar in concept to” range site. However,
the emphasis on climax is similar to the traditional permanent
forest type which is the equivalent of a climax forest association
(Toumey and Korstian, 1947, ps. 384, 392).
key difference between Nichols association-type and the traditional
American (=Clementsian) association was that the former was “not limited
in it’s application to the vegetation of regions which are floristically
continuous”. For instance, the associations of California chaparral
and Mediterranean coastal scrub have no common flora but are regionally
parallel due to “similarity in climatic conditions” and “similar in
their physiognomy and ecological structure” and thus constitute “a
common association-type” (Nichols, 1923, 159). This seemed synonymous
with the biome-type or formation-type described by Whittaker (1975,
p. 128). It appeared similar to the Bailey unit of ecological region
and thus the classic Clementsian formation or regional climax or biome,
all synonyms. Association- type is not identical to these Clementsian
units however as the equivalent Nichols unit to those spatially delimited
ecological units was the geographically defined association-complex.
When Nichols (1923, p. 161) considered geographical distribution of
plant associations (associations of a naturally defined area like
a climatic region at largest scale or physiographically delineated
at smaller scale) he used the term association-complex (vs. association-type).This
too was ambiguous because in “unrestricted usage” association-complex
corresponded to the general term of “community”. In more specific
usage Nichols (1923, ps. 162-165) distinguished between “climatically
and physiographically determined association-complexes”.
(1923) formulated his ecological classification scheme of plant communities
on concepts and terms he had previously introduced (Nichols, 1917).
These principles (Nichols, 1917) were based largely on the work of
Henry Chandler Cowles and the successional theories advanced in the
just-released Plant Succession (Clements, 1916a). (Clements
drew many of his fundamentals from the slightly earlier work of Cowles,
including Clements’ signature concept of “dynamic ecology”.) In his
foundation paper Nichols (1917, p. 312) distinguished between permanent
and temporary plant associations. Nichols’ permanent associations
were limited to what he designated as the regional climax association-type,
the vegetation that has attained “the highest degree of mesophytism
which the climate of the region permits”. Nichols (1917, p. 312) explained
that “it is commonly stated or implied in ecological literature that
in every region, as the logical consummation of progressive successional
changes, the vegetation of all soils and all types of typography is
destined eventually to acquire the same degree of mesophytism that
characterizes the regional climax association-type …” . Here again
is the Clementsian monoclimax theory which Nichols then abandoned
(or, perhaps more precisely, modified) by introducing into the regional
climax association-type (“in edaphically unfavorable situations”)
the plant community unit of edaphic climax association which
was also a permanent association (Nichols, 1917, p. 314-317). Nichols
went on to introduce and describe such units of plant communities
as the edaphic formation, primary and secondary edaphic formations,
the edaphic formation-type, the climatic formation, and the climatic
formation-type (Nichols, 1917, ps. 341-348). He also had community
complexes (eg. climatic formation-complex, edaphic formation-complex,
association-complex) and even presented an example scheme (Nichols,
historically important that Nichols and Clements simultaneously published
views of climax vegetation that ran counter to each other: from the
beginning there were the opposing— at least partially so— interpretations
of monoclimax vs. polyclimax formations. This took place 18 years
before Tansley (1935) brought this to the lasting attention of synecologists.
In other words, contrary to the prevailing and popularized “personality
story” of Clements and Tansley behind the two counter-views of climax,
it was Nichols and not Tansley who first presented what came to
be known as the polyclimax theory.
above, Nichols (1917, ps. 317-318) introduced the unit of habitat-type.
(For whatever reasons, Nichols did not receive the credit for being
the first to publish ideas and major contributions that enhanced reputations
of subsequent authors.) Along with habitat-type Nichols had the unit
of habitat-complex that was “intimately associated with” the
seems to have been the synecologist who first devised a vegetation
classification in which there were parallel— corresponding —units
of habitat equivalent to units of vegetation (eg. habitat-type with
association-type, habitat-complex with association-complex).
most relevant point in this detailed explanation is that the regional
climax association-type corresponds to— and only to— the Clementsian
association (Nichols, 1917, p. 312, citing Clements [1916a, p. 128]).
It is at this point that the word “type” was affiliated with the word
“association” irrespective of how these terms were specifically applied
or how precisely they matched each other.
for Nichols distinguished associations within his unit of ecological
association-type was habitat: “… different associations belonging
to the same association-type will be approximately parallel in their
habitat relations; ie., the nature of the habitat will be approximately
identical wherever these associations occur” (Nichols, 1923, p. 159).
Thirty years later Daubenmire (1952) introduced his vegetation classification
in which habitat type was basis of and commensurate to climax association.The
association-complex was Nichols’ vegetation unit that was determined
geographically by climate or physiography. While these categories
are major parts or components of the abiotic environment (= physical
habitat) they do not comprise the total of habitat. Rather, climate
and physiographic features relate vegetation respectively to Clements’
monoclimax and Nichol’s (later Tansley’s) polyclimax theories.
the physiographic component within the larger climatic component Nichols
aligned his classification of plant communities more closely to that
which came to be attributed to Tansley than to that of Clements (Baker,
1950, p. 40). To be historically accurate, Tansley followed more closely
the vegetational view of Nichols than that of his close friend Clements.
The situation is not that simple however because Nichols (1917, p.
346) cited Tansley in his published review of Plant Succession
(Tansley, 1916, p. 203) as objecting to the exclusive use of climate
while failing to account for “edaphic conditions”. Nonetheless, it
was Nichols who apparently first published a classification of plant
communities that openly broke with the climatic climax (monoclimax)
theory. It apparently was also Nichols who first aligned units of
habitat with units of vegetation (at least within the English or Anglo-American
Tradition). These units were based on and arranged according to the
polyclimax view of vegetation. This clearly predated the same arrangement
(even same unit of habitat-type) of the Daubenmire (1952) classification.
the association-type and its associations amounted to community classification
based on physiognomy and ecological structure, the association-complex
and its associations constituted classification based on geographical
relations. Nichols subdivided his geographically defined association-complexes
into climatic unit-areas (climatic
regions) and into physiographic unit-areas. These in turn were subdivided
into climatic plant formations and physiographic plant formations,
respectively. All of his units were “capable of both concrete and
abstract interpretation” (Nichols, 1923, p. 161-165).
importance of the term and concept of habitat-type by Nichols (1917,
ps. 309, 310) was discussed
above. Nichols included in habitat or environment the three general
categories of: 1) climatic, 2) edaphic, and 3) biotic elements (Nichols,
1917, p. 306) and designated a series of habitats that occur within
the association-complex as a habitat-complex (Nichols,
1917, p. 317). Nichols (1923, ps. 17-23 passim) incorporated habitat in his
plant community classification system to a greater extent than Clements
did in his community hierarchy. In Nichols’ previous paper which laid
the foundation for his plant community classification Nichols (1917,
p. 305) specified that his system was a modification “of the classification
originally devised by Cowles (1901)”.
In reviewing the genesis of climax units of vegetation and
proposing his own interpretation Clements (1916a, ps. 117-128) noted
repeatedly the importance of habitat. Yet Clements stated frequently
that physiognomy and floristics were of more immediate usefulness
than was habitat in delineating vegetation units like formations and
associations though all were seen as “complementary and not antagonistic”
(Clements, 1916a, p. 122). It was development of vegetation that was
the bedrock of the Clementsian paradigm:
is for these reasons that development is taken as the basis for the
analysis of vegetation. It is not a single process, but a composite
of all the relations of community and habitat. It not only includes
physiognomy, floristic, and habitat, but it also and necessarily includes
them in just the degree to which they play a part, whatever that may
be” (Clements, 1916a, p. 123). The formation “is delimited chiefly
by development, but this can be traced and analyzed only by means
of physiognomy, floristic, and habitat. In a natural formation, development,
physiognomy, and floristic are readily seen to be in accord, but this
often appears not to be true of habitat.”
Habitat is “the causal unit”, but “… the habitat can only be
used in a general way for recognizing formations” until there is “…a
much clearer understanding of
the climatic and edaphic factors and the essential balance
between them” (Clements, 1916a, ps.126-127).
is the same philosophy or perspective that Clements maintained when
he adamently refused to include habitat in the biome (Biome section
in reviewing such bases of associations as physiognomy, structure,
climate, and succession, Nichols (1923, p. 172) followed more closely
Gleason (1917) whom he cited twice. Nichols (1923, p. 174) concluded:
it its entirety, an association is characterized throughout by essential
homogeneity or constancy of habitat, but subordinate variations of
habitat within the association make it necessary to distinguish between
the general habitat relations of the association as a whole and the
specific habitat relations or its constituent elements”.
Yet Nichols’ very next point was that the plant association was a vegetation unit that was defined “by its inherent characteristics of vegetative form and structure” (notably physiognomy). Thus Nichols’ ecological association-type was similar to formation and therefore “habitat uniformity is not specified as a criterion” (Nichols, 1923, p. 174).
under the Organicism section below Nichols was the Tansley rather
than the Clements variety of organicist and, as shown previously in
this section of the paper, it was Nichols, not Tansley, who first
put forth a view of vegetation based on what became known as the polyclimax
theory. In applying, at least partially, the Gleason continuum view
of plant communities and the polyclimax theory Nichols’ interpretation
of vegetation was similar yet distinct from that of Clements and yet
also different from Gleason’s individualistic interpretation. Plus,
and perhaps most importantly, Nichols anticipitated by a quarter century
the blending of mono- and polyclimax theories that became Whittaker’s
climax pattern theory.
placed relatively more stress upon edaphic and physiographic features
than on climatic criteria which resulted in use of lower spatial and
shorter temporal scales in analysis of vegetation. In Nichols (1917)
earlier paper, which laid the basis for his plant community classification,
Nichols discussed Clements “developmental concept of the climatic
formation” complete with quotations from Plant Succession (Clements,
1916a, ps. 3, 124-127) on vegetation “as an organism” and “an organic
entity” and the formation as “the final stage of vegetational development
in a climatic unit”, “the highest life-form possible in the climate
concerned”. Immediately thereafter Nichols (1917, p. 346) departed
from Clementsian monoclimax (= regional or climatic climax) and adopted
what was later designated the polyclimax model with edaphic and physiographic
climaxes within the climatic climax:
will be seen from the foregoing quotation that Clements regards the
climatic formation what from the writer’s point of view would be termed
the regional climax association-complex (or association-type). It
is the opinion of the writer that the climax association-complex should
not be so regarded, but that the entire edaphic formation-complex
of the region, or, as before stated, the vegetation of the region
in its entirety, should be considered as constituting a unit from
the standpoint of regional physiographic ecology. It seems more logical
to regard the climax communitites of the region, like other ecologically
parallel series of communities, as belonging to a common association-type.
As the most mesophytic type of vegetation attainable under the existing
climatic conditions, the climax association-type may be looked upon
as the climatic indicator, but not as the climatic formation. To sum
up, the vegetation of any region having an essentally uniform climate
throughout, taken in its entirety, constitutes a climatic formation,
the general ecological aspect of which is determined by that of the
climax association-type of the region".
This is a pivotal passage for several reasons including:
It expanded the climatic
climax from the mesophytic or most mesic form of vegetation of a climatic
region to the whole vegetation of a climatic region (ie. the climax
mesophytic vegetation of gently sloping uplands is no more climax than
climax vegetation of such habitats as xeric south slopes or hydric bottomlands),
|2. It unified monoclimax and polyclimax views even before thay had that designation and were seen later as opposing theories, and it set the stage for Whittaker (1953) to bring these interpretations together using the continuum view of Gleason (1926); interestingly, Whittaker (1953, p. 42) credited Nichols (1917, 1923) with edaphic and physiographic climaxes but he did not remark that in these same papers Nichols initiated the combining of mono- and polyclimax in classification of plant communites,|
It indicated that
soil and landform could be the basis for climax vegetation,
It anticipated by
60-70 years what Bailey (1996, 1998) developed as Ecosystem Geography
and the ecoregion concept; it is interesting here that Bailey made no
reference to the earlier hierarchial system which arranged nested units
and distinctions based on climate, topography, and soils (it was remarked
previously that Nichols’ work has not been given it’s due credit), and
|5. (and most importantly for this discussion of range and forest cover types) it aligned closely the term and vegetation unit of association with the term and generic unit of type and it continued the traditional affiliation of the units of plant formation with plant association in a hierarchial relationship with association being a unit within formation (an arrangement going back to Warming ).|
|The units and details of Nichols’ classification (other than brief description of units that paralleled or anticipated contemporary units like ecoregions) is not the relevant point pertaining to origin of the concept/term of plant assocaition. The key fact is: for all its varied definitions, the hierarchial unit of vegetation or the level of plant community organization designated as plant association is the one that became most closely aligned with what foresters and range managers developed as forest and range cover types. There may have been other plant community or formation (= climax) systems besides that of Nelson, but clearly Nichol’s classification format arranged formations (eg. climatic formation, edaphic formation), types (eg. association-type, edaphic formation-type, habitat type), and associations (eg. edaphic climax association, association-complex) relative to (nested within) one another.|
|Top of page|
|Apparently there was no defining system or point at which the Anglo-American unit of plant association became more or less synonymous (or at least closely resembling) cover type. In fact, this relationship is obtuse and its origin obscure so as to require familiarity with the historic literature in such related but distinct fields as Plant Geopraphy, Plant Ecology, Forestry, Range Management, and Soil Science. In some cases it appeared that the relation of association to cover (= dominance= vegetation) type and these as units within formation was an automatic (or nearly so) arrangement. For example, this pattern was followed in the California Vegetation-Soil Survey (California Forest and Range Experiment Station, 1954; Kuchler, 1967). California Vegetation-Soil Survey classified and mapped vegetation at two levels: 1) vegetation cover classes which were major kinds of vegetation and 2) species types which were based on dominant plant species (Kuchler, 1967, p. 277). The species type is obviously the dominance (= cover) type which is synonymous with vegetation type:|
Apparently there was no defining system or point at which the Anglo-American unit of plant association became more or less synonymous (or at least closely resembling) cover type. In fact, this relationship is obtuse and its origin obscure so as to require familiarity with the historic literature in such related but distinct fields as Plant Geopraphy, Plant Ecology, Forestry, Range Management, and Soil Science. In some cases it appeared that the relation of association to cover (= dominance= vegetation) type and these as units within formation was an automatic (or nearly so) arrangement. For example, this pattern was followed in the California Vegetation-Soil Survey (California Forest and Range Experiment Station, 1954; Kuchler, 1967). California Vegetation-Soil Survey classified and mapped vegetation at two levels: 1) vegetation cover classes which were major kinds of vegetation and 2) species types which were based on dominant plant species (Kuchler, 1967, p. 277). The species type is obviously the dominance (= cover) type which is synonymous with vegetation type:
types by species composition (refered to as “species-types”) are natural
bodies of vegetation classified according to the dominant species
growing together in an ecological association” (Kuchler, 1967, p.
was no obvious author or published system that can be pointed to as
the instant at which association became established as the unit of
vegetation most closely corresponding to dominance type, range vegetation
type, or cover type, but that was the apparent relationship that come
to be accepted within the American-British Tradition in such applied
brances of Ecology or Vegetation Science as Forestry and Range Management.
It was obvious that the various contemporary systems from which the
American concepts of plant association and cover type emerged were
not completely inter-convertible. The above historical review did
indicate (at least strongly suggested) that cover type and its numerous
synonyms as used by ecological practitioners grew out of, and thus
is roughtly equivalent to, the term plant association as developed
and applied by the Anglo-American Tradition. This was largely through
the profoundly influencial writings of F.E. Clements and his colleagues
E. Nichols developed a vegetation classification system simultaneously
with that of Clements. Like that of Clements, Nichols’ system grew
out of the work of H.C. Cowles. Both systems were sophisticated, elaborate,
precisely defined, (and confusing). Nichols’ classification aligned
the specific term and vegetation unit of association with the generic
term and unit of type more directly than did Clements, but applied
ecologists (especially foresters) “associated” association and type
as rough equivalents more through the writings of Clements. (Nichols
did not apply his work as directly to the practical management of
vegetation.) Nichols adopted the view of polyclimax theory, and years
before Arthur Tansley popularized it. Nichols’ view of climax ultimately
prevailed over Clements monoclimax view, but Nichols who published
no epic ecological monographs never gained the recognition or reputation
(or the wrath) reserved for Clements. The original contributions of
Nichols remained largely unknown though some of his concepts like
habitat-type appeared to have been adopted by later ecologists.
apparent from this review of the type concept that origin of the term
is somewhat obscure. The tortuous path of the development of “type”
resembles in its obscurity the development of the vegetation it seeks
to describe. With confusion typical of much of Clementsian theory
and vocabulary the term “type” was also used synonymously with biome
or formation: “… three great types of vegetation, viz., forest, scrub,
and grassland” and “[e]ach formation is the highest type of vegetation
…” (Weaver and Clements, 1938, p. 478). In other words, Clements &
Company used “vegetation type” as a general term for vegetation much
as the Ecological Society of America Vegetation Classification Panel
used it as a generic term. Most other authors seem to have followed
this same format when using the specific words “vegetation type” as
the catch-all collective term for any or all units of vegetation.
Most commonly a combination of the words “vegetation” and “type” was
a generic usage much like “plants”, “cattle”, or “dogs”. Oosting (1956),
Eyre (1971), Shimwell (1971), and among prominent range scientists,
Holechek et al. (1998) followed this common use of “vegetation type”.
Other renowned range authorities ignored the terms “vegetation type”,
“range type”, or “cover type” altogether (eg. Sampson, 1952; Stoddart
et al., 1975). Sampson (1952, ps. 99-102) used the term association
for units of grassland vegetation including tall-grass prairie, short-grass
plains, Pacific bunchgrass, etc. He used the Clementsian definition
and unit of association including consociation (Sampson, 1952, ps.
63-64). That the “Father of Range Managaement” in his last published
textbook used the same (or similar) plant asociations as Clements
(1920) in Plant Indicators and Weaver and Clements (1938) in
Plant Ecology attest to the relatedness of associations to
on historical usage as just described it would seem advisable to
avoid the words “vegetation type” or “types of vegetation”
because these terms or word arrangements
have been used variously or as the generic term for units or
kinds of vegetation. This is consistent with the recommendation of
the Terminology Working Group of the ESA Vegetation Classification
Panel (1997, p.14) which regarded the SRM (1989) term of vegetation
type as the least preferred designation for a unit of vegetation.
Likewise it would be advisable for authors to avoid using “vegetation
types” as the generic equivalent for kinds of plant communities or
hierarchial levels of vegetation. Given the numerous terms of long-standing
use it would avoid confusion to stay with “range types”, “range cover
types”, “range dominance types”, “rangeland cover types”, and “forest
cover types”. As there are various kinds of “forest types” (eg. “forest
cover type”, “permanent forest type”, “climax forest type”, “temporarty
forest type”) as discussed earlier, “forest type” should best be avoided
except as the all-inclusive term for all kinds of forests.
In summary, the cover type concept and the specific recognition/description of cover types as used in Range Management and Forestry is well-founded and traceable back to the earliest, most influencial, and longest lasting literature on the ecology of North American native vegetation. Range (both rangeland and forest) cover types and detailed descriptions of them are current and of considerable value to scientists and professional practitioners. Range cover types are readily distinguishable to students of natural vegetation, and probably also to those such as observant stockmen, lumbermen, sportsmen, wilderness enthusiasts, etc. who are interested in vegetation even if not well-read in the subject.