|Defined and Described|
|Range site has traditionally been defined precisely by the Society for Range Management as:|
|--"an area of land having a combination of edaphic, climatic, topographic and natural biotic factors that is significantly different from adjacent areas" (Huss, 1964),|
|--"a distinctive kind of rangeland, which in the absence of abnormal disturbance and physical site deterioration, has the potential to support a native plant community typified by an association of species different from that of other sites” (Kothmann, 1974), or|
|--"an area of rangeland which has the potential to produce and sustain distinctive kinds and amounts of vegetation to result in a characteristic plant community under its particular combination of environmental factors, particularly climate, soils, and associated native biota" (Jacoby, 1989).|
|Range site is conspicuous
by its absence from all major principles or introductory Range Management
textbooks (going back to the
first by Arthur W. Sampson) except Bell (1973). Heady and Child (1994, p.
138, 143) wrote the terms range site and ecological site but did not define
them specifically except to cite Shiflet (1973): “A unit of land supporting
or capable of supporting a distinctive climax vegetation”.
This vague description obviously could include any unit from as large
as a biome (or formation) down in size to a plant association and finally
as small as an actual range site.
Soil Conservation Service (SCS) relied heavily on range sites and has provided
the most specifics of any organization or individual in this regard. SCS
devoted over six pages in its 1976 National Range Handbook to the use, determination,
permanence, naming, describing, etc, of range sites (SCS, 1976, units 302
through 304). SCS defined range site as:
| --"a distinctive
kind of rangeland that differs from other kinds of rangeland in
its ability to produce a characteristic natural plant community".
|Over many years
SCS range conservationists and specialists wrote hundreds of range site
descriptions. It is logical that the one Range Management textbook that
treated the range site concept was written by a man who spent 30 years as
a range specialist with the SCS.
|In December, 1982 the Bureau of Land Management (BLM) officially adopted the SCS Range Site Inventory method as outlined in the 1976 SCS National Range Handbook (BLM, 1990).|
|The current National
Range and Pasture Handbook of the Natural Resources Conservation Service
(1997) devoted about 56 pages to "ecological sites for native grazing
land". Rangeland ecological site was defined as:
|"a distinctive kind of
land with specific physical characteristics that differs from other kinds
of land in it its ability to produce a distinctive kind and amount of vegetation"
(NRCS, 1997, Section 1, 3.1-1).
|The criteria and basic meaning of range site has remained remarkably consistent over the years, at least among groups subscribing to the basic definition that essentially traces back to the Soil Conservation Service.|
|Range Site vs. Habitat Type|
|Top of Page|
|Site has traditionally had a less specific meaning in Forestry. In one of the earlier references for Forestry terms the Society of American Foresters (SAF) defined site as:|
considered as to its ecological factors with reference to capacity to produce
forest or other vegetation; the combination of biotic, climatic, and soil
conditions of an area" (Munns, 1950).
|Since then the
SAF (Ford-Robertson, 1971) defined site as a synonym for habitat:
|“an area considered in terms
of its environment, particularly as this determines the type and quality
of the vegetation the area can carry”.
|The current SAF definition is identical to the latter except the words “ …in which a plant or stand grows…” followed the word “area” (Helms, 1998).|
|These are similar
to the earlier yet (and even more general) silvicultural-oriented definition
in which "site" was synonymous with "environment":
|-- "The environment
of a forest is very commonly referred to by the term site.
Site as used by foresters is the exact equivalent of habitat as used
by ecologists. It is equivalent to the term locality as used by European
writers on silviculture... In addition to its earlier meaning it has now
become a scientific term applied
to the combination of climatic and soil conditions affecting a plant, which
are incidental to the place in which the plant lives.
...From the standpoint of slivics site may be considered as including
everything relating to the factors operating in a geographically definite
locality so far as these factors influence forest vegetation. Thus site
is very complex, being the result of the interactions of many varying factors...
[T]he term is applied to areas in which all the environmental conditions
are essentially uniform throughout" (Toumey and Korstian, 1947, ps.
|Although this description includes climate, it also specifies soil. While soil could be considered at scales above series (eg. association) or even larger scale (eg. great group), inclusion of the edaphic component in conjuction with climate and the qualifier of uniform environmental conditions clearly connotes a view of site similar to range site and not of larger, heterogeneous vegetation units like vegetation types. Clearly, neither climate nor any other single factor is the principal determinate of forest community.|
|Smith (1986, p. 263) in defining site (again in a silvicultural context) distinguished site from habitat: "While the term site is the traditional one denoting the total environment of a place, habitat more fully connotes the idea that the place is one in which trees and other living organisms subsist and interact". Then in discussing site identification and classification Smith (1986, p. 264) remarked: "The first consideration in site classification is the regional climate". The initial emphasis on regional climate suggest regional not local vegetation (ie. forest type or associations and not vegetation equivalent to the level of range sites). In fact, immediately thereafter Smith (1986, ps. 264-268) used different forest cover types to illustrate site thereby mixing vegetation type and site.|
|Smith then cited Spurr and Barnes (1980) as the reference for site classification. Spurr and Barnes (1980, ps. 297-335) discussed several site classification systems including the Landscape Hierarchy classification scheme of Daubenmire (1968, ps. 259-263). It is this system that has habitat type:|
|--"All parts of the landscape that support, or are capable of supporting, what seems desirable to consider as the same kind of relatively stable phytocoenosis (homogenous as to dominants in all layers) in the absence of disturbance, comprise one habitat type ... Ordinarily one habitat type is highly discontinuous, with intervening areas occupied by other types differentiated by either soil or microclimate". The habitat type is "... the lowest level in an ecosystem classification that aims to reflect potentialities...among layered structure, floristics, dominance, edaphic factors, microclimate, and succession". The potential vegetation is usually climax vegetation (climatic, edaphic, or topographic climaxes but usually only one or two). Plant communities growing on "scattered units of one habitat type usually embrace a wide variety of seral stages as a result of disturbances at varied times in the past", but each seral community "... can be related dynamically to some one primary climax...". Use of potential vegetation irrespective of current successional stage allows "... the closest possible correlation among vegetation, microclimate, and soil" (Daubenmire, 1968, p. 260).|
|Spurr and Barnes (1980, p. 313) cited Daubenmire (1968) and then succinctly defined habitat type as "literally, the type of climax vegetation on a particular habitat or site". Unfortunately, in their brevity they garbled the two vegetation units of site and vegetation type. Still, one gets the general idea that habitat type is similar to, if not the same as, site.|
|Habitat type has
been controversial in the Range Management profession. ("What else
is new?") While the Daubenmire habitat type clearly fits most major
criteria of range site notable range authorities disputed the oft-expressed
assertion that these two terms are synonyms. That range (= ecological) site
and habitat type are "similar" is the current interpretation of
the Society for Range Management. After
restricting habitat type to the vegetation unit of plant association and
specifying the Daubenmire conception, the SRM stated: "Habitat type
is similar in concept to ecological (= range) site. The difference depends
mainly on how specifically plant associations are defined" (Bedell
|This is official, but that alone does not make it correct. Anderson (1983) alleged that range site and habitat type are different because the former "has management implications" while the latter does not. Likewise, range (= ecological) site "is a management tool" while a habitat type "is primarily an academic tool", but "... at any specific location on the landscape, an ecological site and a habitat type are likely to be synonymous" (Anderson, 1983).|
|The enduring Dyksterhuis
entered the fray noting that habitat includes biotic as well as abiotic
factors. He concluded "... that at best the habitat type approach,
with its list of species, is a cumbersome method of designating habitats"
later Daubenmire (1984) responded to the conclusions expressed by Anderson
(1983), but seemingly by trying to write his own restrictive interpretation
of range site by asserting that the term "...suggest a single-purpose
objective, i.e., management of land for producing livestock forage".
In point of fact, as clearly
recorded above in quoting all SRM definitions of range site, the term never
was defined in the narrow sense of "livestock forage". Obviously,
the word "range" has always meant land with native vegetation
serving as feed resources for grazing/browsing animals, but this always
included wildlife the same as livestock. By contrast Daubenmire (1984) pointed
out that habitat type had "... implications for a variety of land management
objectives such as livestock, wildlife and timber production, for predicting
disease hazard, for indicating hydrologic cycles, etc." All these commodities
and processes are common to range and are not excluded by grazing. Range
as defined by the SRM was always compatable with multiple uses, and given
that it is the profession of Range Management represented and promoted by
the Society for Range Management, the adjective "range" would
seem preferable to that of "habitat". This seemed especially obvious
given the attempt by Daubenmire (1984) to strengthen his view by presenting
a commodity-restricted definition of “range” that was never identified or
used by the Society for Range Management.
|Next, biologist G.R. Hoffman (1984) weighed in on the side of habitat type and like Daubenmire stated that these vegetation units do have management implications. "The habitat type concept has been tested in some management-related studies and has been shown to be sound." Mason (1985) proposed "... that range site concept is essentially the same as the habitat type concept", plus “[w]ith very minor modifications they could be exactly the same".|
|There seems to be a consensus among rangemen that range site and habitat type are, if not essentially the same, quite "similar in concept" and perhaps in range practices. Again, the SRM range term glossary (Bedell, 1998) said as much.|
In conclusion, though, that still does not prove that these two conceptually "similar" terms are interchangeable. The most specific observation was perhaps that of Hall (1985). He noted that the habitat types of Daubenmire and Hoffman are floristic classifications of plant communities (climax plant associations, in Daubenmire's words and as noted by SRM) and, as these proponents themselves emphasized, that "topography, soil, and climate are not part of the classification...". This latter point is proven by examples where because plant communities are the same "the same habitat type can occur on low precipitation north slopes and higher precipitation south slopes" (Hall, 1985).
|It is plant community,
and not physical/chemical site factors, that delineate habitat types. By
contrast, it is the abiotic components that delineate, that identify, range
sites. The unique plant communities growing on range sites are determined
by soils, relief, aspect, etc. The range or forest community that is characteristic
for a range site is but a reflection of that unique combination of abiotic
factors, but it is not the unique vegetation as such, at least not the vegetation
alone, that determines the range site. In the case of habitat type, it is
solely the vegetation that distinguishes one habitat type from another.
"The difference between
habitat type and ecological site/range site is the inclusion of abiotic
factors in making the classification for the latter" (Hall, 1985).
|Pfister et al. (1977, p.1) stated that habitat type (as it came to be adopted by the U.S. Forest Service, which probably was what brought it into conflict with range site whether such be admitted or not) was introduced by Daubenmire (1952). Daubenmire’s classic ecological monograph of forest vegetation is highly recommended for its: 1) detailed descriptions of forests throughout a region, 2) application of the plant association concept to vegetation classification (discussed in the Range Types section below), and 3) its “practical applications” to “forest, range, and wildlife management” (Daubenmire, 1952, ps. 324-327). Most importantly for current discussion, this seminal paper in which Daubenmire introduced his version of habitat type seemed to provide the answer to an argument concerning the unit that arose 30 years later.|
|In this descriptive vegetation classification, Daubenmire used two “phytosociologic entities” or vegetation units. The larger and basic unit was the association, specifically the climax association, defined to embrace|
|“all unions that are superimposed
on the same area, and each distinctive combination of vascular unions is
ordinarily considered a separate association. Such an aggregation of union
[“s”, sic] constitutes a phytocoenosis”.
|The other entity
(or synusia) is considered the
smallest structural unit in the organization of vegetation, each union consisting
of a population of one species, or of several species that are closely similar
in ecology (ie. in microenvironmental requirements) as indicated by similarity
of local environmental amplitude, phenology, and frequently by similarity
of life-form as well.” Species making up a union vary “and for the most
part seem a result of historical factors or chance dissemination rather
than of present variation in environmental factors” (Daubenmire, 1952, p.
were the basis of vegetation classification. “Association is a concept embodying
those characters of all actual stands among which differences in species compostion are attributable
to historical events or chance dissemination rather than to inherent differences
in environments. Widely separated dissimilar stands may eventually be shown
to be connected by an intermediate series exhibiting continuous variation
that is correlated with gradual macroclimatic gradient.” An association
is designated and named by the species of a dominant union (the dominant
tree species) and species of a subordinate union (the dominant understory
species). The climax association “extends into distinctly diffferent climatic
regions, and in so doing occupies very diverse soils and topography by way
of compensation” but “each stand contains essentially the same galaxy of
subordinate species …”. This is due to “… intrinsic characters of the habitat
or upon microenvironmental conditions created by the dominant trees”. As
such, “diversity with respect to ecologic role must be subordinated in biogeographic
classification” because “all stands of an association have a high degree
of biotic similarity” (Daubaenmire, 1952, p. 303).
|Next Daubenmire provided a key specific criterion:|
|“In the interest of clarity,
it is desirable to make a distinction between vegetation and the area it
occupies. The collective area which one association occupies, or will come
to occupy as succession advances, is called a habitat
type.” Daubenmire went on to explain that varied habitat factors compensated
such that “the ecologic sums of the different sets of conditions are essentially
equivalent” within the habitat type of a climax association. As such, “the
fundamental characters of the habitat type are not permanently affected
by disturbance” (Daubenmire, 1952, p. 303).
|In this passage, in the subordination of “ecologic role” (ie. habitat), and in the greater importance of “chance dissemination” than “variation in environmental factors” Daubenmire clearly established that it was the climax vegetation and not the habitat that distinguished the association. As discussed below this is consistent with definition of plant association. However, the area occuped by one association is its habitat type so that these two things are just two aspects of the same parcel(s) of land. Most importantly, it was the vegetation that was described and not the habitat. Actually it was the subordinate unions within one zone comprised of one dominant tree species that distinguished one association from another and, by extension, one habitat type from another (Daubenmire, 1952, ps. 306-319, 323). As such, habitat type was in actuality a unit of vegetation and not a unit of the environment, the habitat, in which the vegetation grew. In fact, the habitat (“environmental factors”) was less important than “chance dissemination” in determining species composition of the habitat type! Again, as habitat type is “the collective area which one association occupies”, association equals habitat type. Daubenmire (1952, p. 323) cited previous workers that referred to this as the “vegetation-indicator approach” or the “vegetation-indicator concept” (ie. it is the vegetation that indicates what habitat exist).|
|This is exactly the point that Hall (1985) made when, as quoted above, he noted that habitat types were merely “floristic classifications”. Recent descriptions of habitat types by the U.S. Forest Service gave some reference to habitat factors by including short general sections on soil, climate, fire history, range management, etc. (Pfister et al., 1977; Mueggler and Stewart, 1980). These habitat types are much more inclusive of environmental factors than were the original ones of Daubenmire (1952). Even these expanded habitat type descriptions are obviously defined first by plant community and then habitat variables were added to the defining vegetation.|
|Another factor or aspect of habitat type to be considered when comparing it to range site is size or, more accurately, scale. In his original association/habitat type unit, Daubenmire (1952, ps. 302-303) viewed stands within an association to be at scale of macroclimate (“gradual macroclimatic gradient”, “macroclimatic and geologic variations” [Daubenmire, 1952, ps. 302, 303]). In fact, “ the same climax type extends into distinctly different climatic regions, and in so doing occupies very diverse soils and topography by way of compensation” (p. 303). The union, on the other hand, is comprised of species that have similar “microenvironmental requirements” (“similarity of local environmental amplitude”).|
|Four facts emerged as relevant to the issue of scale from Daubenmire’s units of vegetation and their size relative to environmental features like climate, topography, and soils:|
Habitat type is the collective area of one association (ie.
each association has one habitat type so these are the same size)
Association occurs at the scale of macroclimate (ie. this
means that habitat type has the scale of macroclimate)
|3. Each association is made up of unions.|
|4. Union is the “phytosociological entity” that exists at the scale of microenvironment or local environment, and union is the smallest unit of vegetation.|
|(Obviously the concept of local environment, microenvironment, or microsite could conceivably be reduced to an infinitely small space, as small as that occupied by one plant, say a cubic meter, or even to the space of a root or single root hair. It is equally obvious that microenvironment so defined autecologically would reduce habitat below that of vegetation or the synecological scale. Such restrictions [reductions] on microenvironment of the union would be an absurd strained rationalization to rule out union in order to try to make association (= habitat type) correlate with the scale of microenvironment after the fact. This circular ex post facto reasoning would be meaningless because realistically microenvironment as applied in vegetation classification (which was what the Daubenmire paper was about) must be at the scale of plant communities by definition. This plant community microenvironment is the scale of the smallest Daubenmire unit, the union, not the association.)|
|Range site is the
smallest unit of range (but it is not a unit of vegetation per se) and it
exists at the smallest scale of vegetation habitat.
|Ergo, as habitat
type exists at the scale of associations that can extend across climatic
regions, there is no way that habitat type can be equivalent in size or
scale to range site, which is the smallest unit of range. If any Daubenmire
unit is the equivalent of range site, it has to be the union, the smallest
unit of vegetation in Daubenmire classification. There is simply no way
that habitat type = range site because these two units are of two different
scales in both absolute and relative size.
of Terms Used in Range Management (Bedell, 1998) stated that habitat
type and range site are “similar in concept” depending “mainly on how specifically
plant associations are defined” it mistakenly drew a comparison to the wrong
vegetation unit. It should have used the Daubenmire union not the association.
This is the issue of scale.
|The other issue
was the fact that habitat type is not a unit of habitat at all but a unit
of vegetation, a “phytosociological entity”. The range site is a unit of
habitat that is distinct in being able to support a unique plant community;
the habitat type is a unit of vegetation that bears some relation to habitat,
but not much because even “chance dissemination” is more influencial in
determining vegetation than is habitat. With range site, it is habitat that
is used to distinguish vegetation; with habitat type it is vegetation that
is used to distinguish (sort of that is) habitat.
|A more precise
statement in the Glossary would be: “Habitat type and range site
are dissimilar in concept. The difference depends mainly on how specifically
Daubenmire unions are defined”.
|Conclusion: range site and habitat type are not the same. "They ain't even close." By ignoring abiotic factors, other than indirectly as reflected through plant communities like associations, habitat types are strictly and solely units of vegetation. As such they do not fit into any ordered organization, any hierarchy, of ecosystems or land units that include climatic, edaphic, topographic, pyric, etc. factors. Habitat type as a unit of vegetation could logically be one level (= a unit) of plant community hierarchy much as plant formation, association, and alliance are units of vegetation. Habitat type could not be interpreted legitimately as an ecosystem unit— a unit or level in an ecosystem hierarchy such as those of the U.S. Forest Service or Bailey (1996, p. 23-26). This is because habitat types are strictly vegetation—the flora biota—and include no abiotic factors except those that were described after the vegetation was selected (ie. habitat is not used in the selection of habitat types). Habitat types cannot be part of a land or landscape hierarchy or classification system because, again, there is no land, landform, soil, climate, etc. component except “after the fact” (after the unit was selected on the basis of dominant species in the vegetation). Instead, habitat type is strictly a plant community at some level of vegetation. It is incorrect to include the word “landscape” in “a classification scheme” entitled “A Landscape Hierarchy” (Daubenmire 1968, ps. 259-263) that is not landscape. The “Landscape Hierarchy progresses from smallest unit or lowest hierarchial level of habitat type up through vegetation zone to vegetation province to vegetation region. Daubenmire (1968) incorrectly used “landscape”. His is not a “landscape” but rather a vegetation hierarchy. Neither can it be an ecosystem hierarchy because none of his units of plant community organization were even partly selected on basis of abiotic components of ecosystems or, for that matter, even animal biota. By ignoring the physical/chemical factors—the abiotic agents—of biotic communities in the selection process, habitat type ignores or, at very least, de-emphasizes the ecosystem concept, a bedrock of modern Ecology.|
|Habitat type does
provide a useful unit of vegetation classification, at least in the Daubenmire
Vegetation Hierarchy. Habitat type has been particularity useful for describing
units of forest vegetation, especially as used by the U. S. Forest Service.
|The Forest Service substantially expanded the habitat type as employed by Daubenmire. The statements in the preceding paragraph apply most specifically (but not exclusively) to habitat type as introduced by Daubenmire (1952) and defined/described by Daubenmire (1968). This could be designated the “Daubenmire habitat type” which is in effect the climax plant association because a single habitat type is all land (“the collective area”) occupied by a single association (Daubenmire, 1952, 303). In fact, in this original monograph Daubenmire (1952) designated his units of forest vegetation as associations and not as habitat types. Habitat type was barely mentioned and habitat features were indicated only indirectly by vegetation and none of the association descriptions included other than passing reference to features like soils, slope, or exposure.|
|The Daubenmire habitat type as modified (descriptions expanded and more inclusive of actual environmental variables) by the Forest Service, the “Forest Service habitat type” as distinguished from the Daubenmire association (later, habitat type), is the unit (of vegetation) that is more useful. The above conclusions regarding habitat type are less appropriate for the Forest Service-expanded unit. Consistent with arguments advanced by advocates of the habitat type in the 1980s, the expanded habitat type descriptions do include some actual habitat information (again, after habitat types were distinguished or selected based on vegetation).|
|The “Forest Service habitat type” does resemble, for some criteria, the range site as developed by the Soil Conservation Service. This is obvious for example in the descriptions of grassland and shrubland types in Montana (Mueggler and Stewart, 1980).|
|Indeed, these units could be designated accurately as “Forest Service ecological sites”. These included considerably less detail on soils and geologic material, but sections devoted to grazing responses and general range practices were very similar to those equivalent parts of standard SCS range sites that have been used for years.|
|There is still a fundamental difference between these two units. Range site bases vegetation on habitat, the abiotic environment primarily, and is thus a unit of habitat classification. Habitat type bases habitat on vegetation and is a unit of vegetation classification. The former starts with habitat and “builds” vegetation descriptions from it; the latter starts with vegetation (dominant species) and develops habitat descriptions from the plant community. As explained in the Range Types section below dominant species have always been used to designate plant associations, and habitat types as used by Daubenmire are units of potential associations. Again, when he first introduced this vegetation classification, Daubenmire (1952) called his vegetation units associations and not habitat types. It seemed that for practical purposes habitat types were (are) associations by another name.|
|The distinct difference between habitat type and range site and the impossibility of interpreting these two as synonyms is discussed further under the Range Type section below. There it is shown that Daubenmire (1968, p. 32) in his Synecology textbook reinterated that habitat type is all the area that can support (has potential to support) one climax plant association.|
|Range Site: A Unit of Habitat|
|Top of Page|
|Important point: range site (and the slightly different forest site) is a unit of land and not solely vegetation. This is obviously essential for the concept to have any utility because range (rangeland and forest range) is the land and not just the vegetation. In fact, “land” includes all natural resources involved in production of the forage and/or browse crop. In the ecosystem concept, this includes light which, though a feature or factor of atmosphere and not land, is affected by the upperstory vegetation as light is filtered to the understory on forest range sites, especially transitory forest ranges. Nonetheless, the range site is not a unit of vegetation; it is a unit of land supporting vegetation (ie. range site is a unit of land including the vegetation it supports). Range site is a unit of native grazing land, but not a unit that is limited to the vegetation. (Habitat type is a unit of vegetation and only or, at least, primarily vegetation because no other aspect or factor is used in its selection.) As such: range site does not fit into a hierarchy of vegetation. Range site is not a subunit of the plant community or even of the plant and animal community. Range site is not a subset of the biome or a subdivision within the plant association or the range or forest cover (= dominance= vegetation) type. All these larger or broader hierarchial levels are limited to the biotic community in case of biome or formation and the plant community in the instance of the plant association. Range site is both smaller (more restricted) and more encompassing than these upper levels of community organization because: 1) range site is the smallest unit of a unique plant community (smallest hierarchial unit that includes vegetation) but 2) directly inclusive of abiotic factors, especially soil, topography (slope and aspect), and landform. Range site goes beyond (includes factors besides) vegetation as the smallest unit theoretically capable of unique management. Thus, range site is not comparable to a range biome (say, grassland or desert) or a range cover type (say, semidesert grassland or mixed prairie grassland). Range site is not, strictly speaking, a logical reduction of range vegetation types which again are units of vegetation only. Range sites fall within range cover types and can be visualized as residing therein, but these most unique kinds of range are land or habitat units (these include the vegetation, but also soil and other natural resources). Range sites are not vegetation units; they are not part of vegetation classification.|
|In conclusion: habitat types appeared to have more limitations in designating units of range. Habitat types are units of vegetation, the descriptions of which can include details of habitat. Range sites are units of range including biotic and abiotic factors. Range sites are units for management of range and not for classification of vegetation; habitat types are units in a vegetation classifiction scheme and have less application for range or forest management practices because they are pre-selected on basis of vegetation alone.|
|The U.S. Forest Service has defined range site noticeably different from the SCS-SRM concept. A typical example from the California Region is:|
|"Range sites are broad, ecologic areas within which soils, climate and other environmental factors of strong similarity exist or are potential" (U.S. Forest Service, 1969, 160).|
|At first flush,
this seems consistent with the definitions and concept above, but the emphasis
on "broad" is substantially different, in contrast to the more
restrictive scale of interpretations by the SCS and, to a somewhat lesser
extent, standard Forestry texts.
with range site the Forest Service used the units of vegetation type and
their subtypes. The latter were defined as: "A subtype is a relatively
large portion of a vegetation type which appears significantly different
in composition, slope, site, density, trend or condition class (U.S. Forest
Service, 1969, 150-1). Vegetation types appeared to correspond to generally
accepted views of cover type with examples including pinyon-juniper, annual
grass savanna, annual grassland (U.S. Forest Service, 1969, 150- 4 and 150-5).
Others are broader or more general (eg. meadow, sagebrush, conifer; 150-
2, 150-3). However, the real difference—going back again to the criterion
of "broad"—between Forest Service and the other interpretation
of range site is that the Forest Service range site can encompass several
vegetation types. For example: "Various vegetation types ... may exist
on any or all of these range sites" (U.S. Forest Service, 1969, 160).
|Clearly, Forest Service range sites are of greater scale than vegetation (= cover) types given that the latter exist inside the former. This is just the opposite of the SCS-SRM perception of range site. Furthermore, and probably because of the larger size of range sites, the Forest Service has made little use of the range site as either a concept or as a unit for analysis and management. This is in contrast to the other two major Federal agencies dealing with range conservation. Historically it has been the range (= vegetation) types that are mapped and serve as the basic units for Forest Service range resource inventories (U.S. Forest Service, 1964) and range analysis of allotments (U.S. Forest Service, 1964, 1970).|
|The more traditional interpretation of range site (eg. the series of SCS-SRM definitions) is that range site is the smallest unit or kind of range that can be recognized and distinguished as unique. It is the least scale of range that could in theory be managed. Almost all managed parcels of natural pasture (termed variously as ranges, pastures, allotments, traps, paddocks, etc.) will have several to many range sites. Thus these range sites are not managed separately (ranges or pastures not range sites are the management units) but, as with individual forage species, each unique range site contributes to the pasture or range plant community that is managed as a collective whole.|
|In theory, range site is the smallest distinctive (recognizable or discernable) unit of native grazing land. This unit consist of the range environment, especially soil, and the unique potential vegetation that is the highest ecological state possible for that environment. Range site is the most specific (relatively smallest) unit of potential natural vegetation (usually climax vegetation) for each specific habitat of natural pasture that is capable of being identified and managed.|
|In the context
and vocabulary of taxonomy, range site is the "lowest" (at the
bottom of the taxonomic hierarchy), smallest, most precise "taxon".
Range site can be visualized as “the species level or unit of range”. Range
site is roughly analogous to species of organism or series of soil. It is
analogous, not homologous, because classification of vegetation is classification
and not taxonomy. At least this is the case when the arrangement of units
is not necessarily based on relatedness (not phylogenetic; the hierarchy
is not consistently based on origin). This seems more likely to be so when
classification of land and its vegetation is based on the use to which that
land and vegetation are put (eg.
classification of land for agricultural purposes vs. taxonomy of soil; classification
of range [natural vegetation used for grazing/browsing], vs. a more taxonomic
classification of, say, grassland, forest, or desert).
Clements took as the
basic pattern for his model of plant succession the Geographical
Cycle Theory of William Morris Davis. In Davis' theory land forms
were formed primarily by land wasting due to climate both directly
and indirectly (Davis, 1898, chapter XI, Climatic Control of Land
Forms). Atmosphere and oceans directed the cycles of building up
and wearing down of land and thus indirectly (as well as by direct
controls) determined plant and animal life on Earth. As such, Clements
interpreted succession as a series of nested seres and cycles within
one another corresponding with the cycles of land formation. Clements'
time scales were thereby inherently those of geologic time, at the
longer span, and of the age (time duration) of a given climate at
the shorter span. Clements' spatial scale was that corresponding
to the size of climates, usually of a regional scale. As mentioned
below in the Biome section below, the latest version of Holism applied
at regional scale is the ecological region or macroecosystem devised
by R.G. Bailey (1996, 1998) as units in Ecosystem Geography. In
Bailey's system of ecosystem classification and hierarchy one hears
the echo of Davis, Cowles, and Clements. Further discussion of
the role of Davis' theory of geological cycles was presented in
the Origin of Clementsian Organicism portion of the Organicism section
Clements took as the basic pattern for his model of plant succession the Geographical Cycle Theory of William Morris Davis. In Davis' theory land forms were formed primarily by land wasting due to climate both directly and indirectly (Davis, 1898, chapter XI, Climatic Control of Land Forms). Atmosphere and oceans directed the cycles of building up and wearing down of land and thus indirectly (as well as by direct controls) determined plant and animal life on Earth. As such, Clements interpreted succession as a series of nested seres and cycles within one another corresponding with the cycles of land formation. Clements' time scales were thereby inherently those of geologic time, at the longer span, and of the age (time duration) of a given climate at the shorter span. Clements' spatial scale was that corresponding to the size of climates, usually of a regional scale. As mentioned below in the Biome section below, the latest version of Holism applied at regional scale is the ecological region or macroecosystem devised by R.G. Bailey (1996, 1998) as units in Ecosystem Geography. In Bailey's system of ecosystem classification and hierarchy one hears the echo of Davis, Cowles, and Clements.
Further discussion of the role of Davis' theory of geological cycles was presented in the Origin of Clementsian Organicism portion of the Organicism section below.