Semidesert Grassland

The semidesert grassland complex of climax range communities comprises the most xeric grasslands in North America. There are two general regions of semidesert grassland in North America both of which are associated with the Basin and Range physiographic province and major climatic deserts therein. The larger and better known of of the two regional semidesert grasslands (grassland complex) is that affiliated with the "warm" Chihuhuan and Sonoran Deserts. The Chihuhuan-Sonoran regional unit of pre-Columbian climax range vegetation dominated by grasses occurred as both 1) a transition zone (= ecotone) between semiarid prairies and plains grasslands and natural desert scrubland and 2) a mosaic of smaller grasslands and areas of Chihuhuan and Sonoran Deserts. Pre-Columbian semidesert grasslands of the Chihuhuan and Sonoran Regions generally extended from portions of Trans-Pecos Texas and Chihuhua across Arizona and Sonora into southern California. Expansion (desertification by invasion of woody plants) of Chihuhuan and Sonoran Desert vegetation onto virgin range on which natural climax vegetation was xeric grassland has resulted in expansion of disturbance climax of desert scrub and corresponding reduction of climax semidesert grasslands. The main outline of original pre-white man and disturbance-retracted margins of the xeric semidesert grasslands were and remain more-or-less conterminous with the semiarid mixed prairie and shortgrass plains grasslands of the Great Plains on the north and east. To the west and south the drier semidesert grasslands are "constant contact" with the various subdivisions of the Chihuhuan or Sonoran Deserts.

The second (and considerably smaller) of the regional semidesert grassland formations is that associated with the "cool" Great Basin Desert and, marginally, the "transition" Mojave Desert. Great Basin semidesert grasslands were considerably smaller and much less frequent in ocurrence as potential natural (pre-Columbian) range vegetation. The widely scattered and smaller semidesert grasslands of the Great Basin occurred between the semidesert grasslands and desert shrublands of the Chihuhuan-Sonoran Regions to the south and the shrub-bunchgrass steppe of the Columbia Plateau to the north. Current generalized distribution coincides roughly with pre-Columbian boundaries as they have been interpreted in studies and maps of natural vegetation. Relatively limited occurrence, along with small and restricted patial scale-pattern, of these dry grasslands is even more so on existing Great Basin range where desertification and expansion of human settlement has been pronounced. In fact--as was explained below--semidesert grasslands of the Great Basin were often completely ignored in detailed treatments of semidesert grasslands. Semidesert grasslands of Intermountain North America were recognized and described briefly by some of the better-known and more experienced students of Great Basin vegetation, but overall these xeric grassland ranges received but a pittance of the coverage given their counterparts to the south.

Technical note on syntax- Deserts are deserts, grasslands are grasslands. One of these biomes cannot be the other anymore than a forest can be a desert. One would never speak of a desert forest. So why use the oxymoron, "desert grassland"? The difference in life form of dominant plants is greater between grassland and desert (herbaceous species vs. woody plants) than between forest and desert (woody plants dominate both). The range vegetation described below is semidesert (a usage deemed to be self-explanatory and one of long-standing precise usage) grassland. Traditional titles in the historic literature such as "desert grassland" and, especially, "desert plains grassland" were shown when such titles were essential in discussion of particular papers or perspectives of specific authors.

Chihuhuan and Sonoran Deserts and semidesert grasslands are closely allied--in both space and in ecological, especially successional, relations-- such that the two major units of range vegetation cannot be satisfactorily described or understood without considering both simultaneously (at least by way of introduction). Beginning with Shrevve (1917, p. 123) through Clements (1920, ps. 145, 162, 163, 169), Weaver and Clements (1938, p. 525), Shreve (1942), and Dick-Peddie (1993), this latter following Shreve (1942), vegetation scientists recognized a regional or zonal vegetation entitled variously the Desert-Grassland Transition (Shreve, 1917), Desert Grassland Transition Region (Shreve, 1942). desert savanna (Shantz and Zon, 1924), and desert shrub grassland (Darrow, 1944). Dick-Peddie (1993, ps. 106-107, 131-132) discussed this large ecotone under both Desert Grassland and Chihuhuan Desert as if this transition zone encompassed both of these divisions of different biomes..

Shreve (1917, map plate, 123) described Desert-Grassland Transition as: "A regioin intermediate in character between the Grassland the Succulent Deserts of Texas and Arizona". From descriptions by the above cited authors the boundary seemed to be more in doubt between the Chihuhuan (than Sonoran) Desert and semidesert grassland. Community appeared to be "in the eye of the beholder". [Hint to Gleasonians: this would seem to be an outstanding example of vegetation as evidence for the individual theory of plant associations (Gleason,1917, 1926).] That both Chihuhuan and Sonoran Deserts are affilitated and related to semidesert grassland is incontrovertible, but the nature of the relationship (evolutionary, successional, floristic, etc.) remains unknown and, as with some much about this range vegetation, open to interpretation.

Over the last 100 to 300 years the successional-community development relationship has been "one way" with the multi-faceted forces of desertification causein conversion of climax semidesert grasslands into desertscrub. In this on-going range retrogression desert shrubs continue to invade the grassland so that the desertland increases while grassland decreases. This desert encroachment and commensurate loss of semidesert grassland has been especially dramatic along the contiguous edge of the Chihuhuan Desert and the semidesert (Chihuhuan) grassland, a transition zone or desertscrub-semidesert grassland ecotone, where vast acreages of disclimax (= disturbance climax) Chihuhuan Desert have developed over the last one to two centuries.

Most of this degradation of semidesert grassland into desert (= arid shrubland or arid scrub) was induced by actions of European man so that the woody invasions constitute an anthropogenic disclimax desertscrub (ie. a man-made desert). The major adverse human impact responsible for this range deterioation has traditionally and consistently implicated overgrazing (and some overbrowsing of palatable woody range plants) by livestock (Clements, 1920, ps. 145-146, 148; Weaver and Clements, 1938, ps. 525-526, 537; Dick-Peddie, 1993, ps. 107-109; 131-132; Holechek et al. 2004, p. 101; Gibbens et al. 2005, ps.665-666). Other factors that have been implicated range from relatively recent severe or extraordinary drought, suppressation of fires or changed fire regimes, and increasing atmospheric carbon dioxide. It was even postulated that certain dominant grasses like black grama (Bouteloua eriopoda) could only retain their dominance during cooler climates such as minor Ice Ages that ended a century ago ((Gibbens et al., 2005, 666). Consensus (by no means unanimity) of scientific judgment clearly implicates past overgrazing by livestock (especially during early Spanish-Mexican and frontier Anglo-Saxon open range ranching eras) and periodic, prolongued droughts as major causes for range degradation including brush invasions. It is almost a given that these two factor resulted in compunded if not synergistic impacts that favored increases in woody species and decreases in palatable climax grassses.

Among affects of livestock grazing the two most obvious were 1) dissemination and perhaps even scarification of mesquite (Prosopis glandulosa) seed when the flavorable and nutritious legume fruit ("bean pods") were eaten and 2) shifting of competitive and survival advantage from climax grasses to less palatable species (especially shrubs and suffrutescent plants) when grasses were defoliated --often at repeated continued high degrees of use so as to constitute overused-- and woody plants were ungrazed or only lightly browsed. The latter phenomenon was explained well by Burgess in McClaran and Van Devender (1995, ps. 46-49).

Other workers (Humphrey, 1958, ps. 51-62; McClaran and Van Devender (1995, ps. 131-141, 242, 244, 249,251-252) have made much of the interaction of livestock grazing and fire. With heavy utilization of herbaceous species by livestock in early ranching eras there was inadequate fuel for range fires. Fire typically induces comparatively more stress on woody plants having their perennating parts within "easy reach" of fire (phanerophytes and chamaphytes) than on herbaceous species like the grasses with perennating plant parts at or below soil surface (cryptophytes or geophytes and hemicryptophytes). Humphrey (1958, ps. 51-62; 1962, ps. 155-165) considered in depth the role of fire in semidesert grasslands. Humphrey was a "born-again" range-burner and concluded that the semidesert grassland was not, contrary to the Clementsian view, a climatic climax but "a subclimax maintained by fire", and he was unequivocal in his conclusion (Humphrey, 1962, ps. 163-165).

Upon subsequent and more investigations it became obvious that the Humphrey hypothesis was too general. Burgess in McClaran and Van Devender (1995, p. 45) concluded that it was incorrect "... to assume that fire is a universal feature of desert grasslands". The various species of plants in this range type vary greatly in their response to fire. Most importantly, grass species in semidesert grasslands vary in their response to fire (Burgess in McClaran and Van Devender, 1995, p. 45; McPherson in McClaran and Van Devender, 1995, ps. 134-141 passim). For example, tobosagrass (Hilaria mutica) tolerates fire and recovers quickly from it whereas black grama recovers slowly following burning (Burgess[citing several studies] in McClaran and Van Devender, 1995, ps. 45-46). These are the two dominant plants on many semidesert grasslands in climax condition; tobosa dominating clay swales and black grama the dominant on sandy upland ranges. A fire burning across one large range on one ranch could thus have drastically different effects on depending on range site (say, swale vs. sandy loam).

The grazing X fire interaction on semidesert grassland has an interesting "twist" when certain exotic grasses that were introduced as complementary pasture or as a species for revegetation can invade semidesert grasslands. Lehmann lovegrass (Eragrostis lehmannii), which was discussed herein under the Introduced chapter of Grasslands, has proved invaluable for revegetation of abandoned cropland and drastically altered lands such as mine spoils, soil and water conservtion, and generally as a naturalized range grass. It also has the ability to become a serious weed when under certain contitions it invades native semidesert grasslands, sometimes those in high successional status. Lehmann lovegrass has the ability to dominate semidesert grassland ranges following disturbances like drought and fire because it reseeds readily whereas sexual reproduction is more limited and recovery by asexual reproduction is slower in the native climax grasses. Range fires at high frequencies selectively favor (shift the competitive advantage to) Lehmann lovegrass over natives, especially those with a fairly low tolerance to fire (eg. black grama, the regional dominant grass). Under such situations proper livestock grazing by reducing fuel loads can help maintain native grassland ranges. Elimination or even reduction of domestic grazing could result in deteriorated semidesert grassland ranges by aiding establishment (invasion by) undesired non-native grass species like Lehmann lovegrass (Roundy and Biedenbender in McClaran and Van Devender, 1995, ps. 293-294Roundy and ). This is an example of the necessity of management in range management.

While all contributing causes and interactions for range retrogression will likely never known, and therefore will continue to be debated, one ecological phenomenon that no one knowledgeable of semidesert grassland ranges challenges is past and present encroachment of woody vegetation into grassland. This on-going woody invastion has been to the extent that the Chihuhuan Desert has expanded northward and eastward while the Sonoran Desertscrub has made similar advances including expansion into foothill slopes that were formerly desert grassland ranges. So rapid has been this vegetational change-- again, much, probably most, was human-induced-- that much of the desertification has occurred during the course of a human lifetime.

Worse, it seems probable that this range degradation will continue. The combination of deep taproot and wide-reaching laterals make root systems of many of indigenous desert shrubs (see Bender, 1982, figs. 9-2 and 9-5, ps. 423 and 430; McClaran and Van Devender, 1995, figs. 2.1, p. 34) much more competitive and better able to survive drought than the native grasses.After discussing superiority of shrub root systems, Gibbens et al. (2005, p. 666) applied the state and transition model and disequilibrium concept (Friedel, 1991 and concluded that "... the change from grassland to shrubland has passed a threshold ... and manipulation of grazing pressure will not reverse the process".

To some extent this was textbook knowledge decades ago. In the confusing terminology of the elaborate, geologic age-based Clementsian system Weaver and Clements (1938, ps. 525-526, 537) said much the same thing when they wrote that numerous shrub species had "...so increased by overgrazing as to simulate a scrub climax" and "... a disclimax of annual grasses ... and forbs" with a desert scrub that had "...greatly increased during the historical period ... " and having "...all the appearance of a true climax". Writing 67 years before Gibbens et al. (2005), and using the monoclimax theory, Weaver and Clements (1938) provided a less conclusive discussion, but the very designation of a "disclimax" or the appearance of a climax said the same thing (only in the code of another system to explain vegetation dynamics). With disturbance climax (= disclimax) described as one of several other kinds of climax and with many examples provided (Clements, 1936, ps. 265-266; Weaver and Clements, 1938, p. 86) is was clear that disturbance-induced shrubland which replaced semidesert grassland was 1) the now potential vegetation and 2) it was probably permanent in human-time scale. Whitfield and Anderson (1938) wrote in the monoclimax-based system of their day and designated a "creosotebush disclimax" and a "mesquite-acacia postclimax" both of which had increased "as a result of disturbance". These early range conservationists were more optimistic regarding recovery of the natural desert grassland vegetation "if properly handled" (Whitfield and Anderson, 1938, p. 176), but they documented conversion of grassland to shrubland having understories of annual weeds. The Clementsian disclimax concept was retained and used in the biotic community classification of Brown et al. (1998 ps. 12, 40) with "desertified" semidesert grassland designated Shrub-Scrub Disclimax Series.

Given the de facto type conversion of semidesert grassland to anthropogenic (disclimax) Chihuhuan Desert it was seen as axiomatic that such NeoChihuhuan Desert range should be treated under the Chihuhuna Desert chapter (Shrublands). That treatment included discussion of the Chihuhuan Desert-semidesert (Chihuhuan) grassland ecotone or transition zone in the context of desertification.

Treatment of semidesert grassland range cover types in this Grasslands chapter was limited to climax grasslands, including grass-shrub savannas. Coverage was consistent with rangeland cover types recognized by the Society for Range Management (Shiflet, 1994). Some of the climax (potential natural vegetation) forms of semideset grassland that have been recognized and described by other accepted authorities (eg. National Park Service) were not included in Shiflet (1994). Some of these omitted semidesert grasslands (cover types) were covered below.

There are several forms (range cover or dominance types) of semidesert grassland and semidesert grass-shrub savannahs. These are zonal (= regional) and/or "patchy" (local in occurrence) with distribution of the range types often determined by physiographic (eg. such topographic features as slope and aspect), elevational (which may coincide and interact with physiography), edaphic (including soil texture, structure, fertility, and frequently above all else, water-holding capacity), and precipitational or thermal conditions.

Choices as to which grassland range types to include under a chapter entitled Semidesert Grassland was based on vegetation historically described as "desert grassland" or "desert plains grassland" (Clements, 1920, ps. 144-149; Weaver and Clements, 1938, ps. 525-526; Oosting, 1956, ps. 333-334; Humphrey, 1958, Shelford, 1963, ps.359-364; Daubenmire, 1978, ps. 202-204; Vankat, 1979, ps. 169-170; Dodd in Gould and Shaw, 1983, ps. 355-356; Sims in Barbour and Billings, 1988, ps. 280-281; and Dick-Peddie, 1993, ps. 106-110, 116-120). This corresponds approximately to the broader vegetation map unit, Grama-Tobosa Shrubsteppe of Kuchler (1964, p.58). Unfortunately (in this author's opinion) The Desert Grassland (McClaran and Van Devender (1995), which should by all appearances be the magnum opus on this grassland, so "mixed-up" semidesert grassland with the geographically and floristically aligned mixed prairie, especially shortgrass plains, and adjoining Chihuhuan and Sonoran Deserts that even those experienced with semidesert grassland ranges were left wondering whether the vegetation described was indeed "desert grassland, mixed shrub savanna, shrub steppe, or semidesert scrub?" (Burgess in McClaran an dVan Devender, 1995, p. 31).

It seemed unavoidable that grassland vegetation included below would be somewhat arbitraty and therefore controversial. For the record, however, range types chosen for inclusion followed the classic or traditional delineations of the previous ecologists listed above. The main defining criterion for these semidesert grassland range types (ie which types to include hereunder) was dominant species. This was seen as the least arbitrary basis (and certainly a difficult-to-debate one) given that cover types are by definition dominance types (Whittaker, 1975, p. 128-129; Whittaker, 1980, ps. 59, 67-79). and that Society for Range Management rangeland cover types (Shiflet, 1994), which "covered" semidesert grassland vegetation, were titled and described as to major or defining (ie. dominant, associate, and indicator) plant species.

Dintinction of semidesert grassland from mixed (mid-grass) and shortgrass prairie vegetation will always be the most difficult separation among closely affilitated range cover types due to commonality of almost all grass species in most range sites of these three broad, general forms of semiarid grasslands. Use of dominance as the key criterion, along with associate and indicator species, permitted separation of semidesert grassland range types from the mixed and shortgrass range types of plains-mesa grassland and, in eastern portions, from those of Chihuhuan Desert (Dick-Peddie, 1993, ps.104-110, 113-120, 131-132, 140-141).Thus, climax grasslands dominated or co-dominated by blue grama (Bouteloua gracilis), sideoats grama (B. curtipendula), curly mesquite (Hilaria belangeri), buffalograss (Buchloe dactyloides), New Mexico feathergrass (Stipa neomexicana), little bluestem (Androgpgon scoparius= Schizachyrium scoparium), or sand dropseed (Sporobolus cryptandrus) --regardless of climatic, edaphic, topographic, or any other habitat features-- were, with but few notable exceptions, automatically included with and treated as "plains-mesa grassland", Great Plains and foothills of various mountain systems of Dick-Peddie (1993, ps. 104-106), and covered under the chapters, Mixed Prairie and/or Shortgrass Plains.

Such separation was consistent with traditional interpretation and treatment of "desert grassland" or "desert plains grassland" by the many workers cited earlier. It differed from that by Whitfield and Beutner (1938) and Whitfield and Anderson (1938) who divided the "desert plains grassland" into the Bouteloua-Hilaria faciation (black grama-tobosa community) and Hilaria-Bouteeloua faciation (curly mesquite-blue grama community). This was consistent with the "pure-milk" of Clementsian terminology, but inconsistent with interpretation of grassland vegetation by Clements (1920) and Weaver and Clements (1938) and their "descedents", all of whom included Great Plains and foothill-mesa range communities dominated by curly mesquite and/or blue grama in the mixed and shortgrass prairies.

Precise placement-- based on dominants (= dominant plant species) and, to lesser extent, indicator species-- means that semidesert grassland could develop "side-by-side" (contiguous) with mixed prairie, Chihuhuan or Sonoran Desert or, even rarely, pinyon pine-juniper woodland. This is consistent with desert range cover types exiting immediately adjacent to riparian forest types, plains-mesa grassland types in contact with pinyon-juniper woodland types or, even, montane forests, and alpine range types conterminous to subalpine forests. Any given range or pasture (grazing unit) could, if sufficiently large or occupying mountainous terrain, include any number of such range cover types and, more yet, range sites.

Proximate location of one range plant community type to relative to other range community (even if these communities are of different biomes like grassland vs. desert vs. forest) means absolutely nothing with regard to designation and description of range cover types, except as this is related to ecotones between or among them. In the case of such transition zones, the range vegetation may be a distinct-- a "hybrid"-- range community requiring designation as its own range cover type. Most of these ecotones as between semidesert grassland and desert or semidesert grassland and woodland are savannas. Herein such composite range plant communities were identified, named, and described as savannas.

All range types and range sites of semidesert grassland include woody (many of them succulent) species so that a shrub and/or tree layer can be interpreted as being present so that the vegetation could be regarded as a savanna. It was explained earlier that some students (eg. Shreve, 1942) viewed this entire zone of range vegetation (= the regional climax) as an ecotone or ecotonal (transition) area or region. In the view of most students, including this one, the arboreous or arborescent species like the soaptrees and Spanish daggers (Yucca spp.) and joint-fir or Mormon tea (Ephedra spp.) are so widely spaced that semidesert grassland, except in true transition zones between adjacent grassland and shrubland, is part of the general grassland biome or formation. Dominant grass species are beyond doubt affiliated and aligned taxonomically and floristically with the Great Plains grassland. Shrubs and, infrequently, small trees are no more prevalent on semidesert grassland than, for comparison, are large trees and shrub thickets on tallgrass prairie.

Major types of semidesert grassland include:

1. Black grama grassland- Black grama has typically been interpreted as the regional dominant of semidesert grassland. The black grama-defined range cover type occurs primarily on sandier soils on upland range sites. This is a predominant landscape or terrain throughout much of the Basin and Range physiographic province so upland black grama range is the regionally dominant form or range type of semidesert grassland.. In this type black grama is the obvious dominant where major associates include tobosagrass, bush muhly (Muhlenbergia porteri), mesa dropseed (Sporobolus flexuosus), and red threeawn (Aristida longiseta) or some member of the purple threeawn (A. purpurea) complex. Miscellaneous species vary with range site and can include more mesic "mid-grass" species such as sideoats grama (Bouteloua curtipendula) and cane bluestem (Andropogon barbinodis= Bothriochloa. barbinodis). Exact species composition and structure of a given range plant community depends on range site and range condition (successional statue). On soils overlying gypsum black grama is frequently co-dominant with alkali scaton (Sporobolus airoides) to form what was described by the Society for Range Management (Shiflet, 1994) as the Black Grama-Alkali Sacaton rangeland cover type (SRM 702).

On upland semidesert grassland ranges in excellent condition black grama develops into nearly "pure stands" and forms a consociation with shrubs of liliaceous or gramineious form. Dick Peddie (1993, ps.116-118, 131-132, 140) concluded that presence of soaptree (Yucca elata) and longleaf jointfir or longleaf Mormon tea (Ephedra trifurca) were diagnostic (= climax) or indicator species whose presence distinguished semidesert grassland. The forb known as desert holly (Perzia nana) and the short fluffgrass (Tridens pulchellus) were also interpreted as possible indicator species of semidesert grassland. Dick-Peddie (1993, ps. 131-132) felt that these species, even as rare remnants, were relict (climax) members that served to distinguish semidesert grassland from anthropogenic Chihuhuan Desert.

Black grama is also a major componment and often dominant species of Great Plains grasslands. The Socity for Range Management (Shiflet, 1994) described Black Grama-Sideoats Grama and Blue Grama-Sideaots Grama-Black Grama rangeland cover types (SRM 703 and SRM 707), but these are not range types of the semidesert grassland. Mere presence of black grama does not denote semidesert grassland.

2. Tobosagrass flats- Tobosa makes up the second most widespread and common rangeland cover type of semidesert grassland. It frequently develops as a consociation on swales having clay soils. Such range sites are usually called by such generic names as "tobosa flats", "tobosa swales", or "tobosa clay flats". A characteristic distinctive shrub on tobosa-dominated lowlands is littleleaf sumac (Rhus microphyllum). Tobosagrass is an associate to black grama on sandy uplant range sites. The two species are sometimes co-dominant in ecotone communities where upland and lowland range sites meet.

Black grama and tobosa comprise the two major range types of the of what could be described as the semidesert grassland division of the North American grassland biome or the semidesert grassland subbiome. These two grassland range types were frequently placed together as a larger climax unit such as the Bouteloua-Hilaria faciation (Whitfield and Brutner, 1938; Whitfield and Anderson, 1938) in language of the Clementsian model (Clements, 1936). Warnock in Shiflet (1994, p. 92) remarked that previous workers had recognized a Bouteloua-Hilaria mutica association.

The Society for Range Management (Shiflet, 1994) lumped the distinct, and usually spatially separated, black grama and tobosa range types into the Grama-Tobosa- Shrub rangeland cover type (SRM 505), but recognized three variants thereof: pure black grama grasslands, tobosa grasslands, and blue grama-black grama grasslands. Apparently the latter develop at upper elevations adjacent to pinyon pine-juniper woodlands or as a transition form to mountain scrub (Gibbens in Shiflet, 1994, p. 65). In the current publication blue grama-black grama (or any other widely distributed blue grama-dominated grassland) was interpreted as part of the plains-mesa grassland (Dick-Peddie, 1993) and treated thereunder.

Historical "quickie": In review of cover types (Range Types under Literature Review herein) it was noted that range cover types are dominance types that basically originated with the vegetation unit, association, especially as it was interpreted, modified, and applied by the Clementsian school. Numerous of the recognized rangeland and forest cover types are synonymous with Clementsian associations when faciation was ignored. Such is the case with Bouteloua-Hilaria mutuca association and Grama-Tobosa-Shrub rangeland cover type (SRM 505). As originally envisioned and strictly arranged, the Bouteloua-Hilaria faciation (Whitfield and Brutner, 1938; Whitfield and Anderson, 1938) was a subunit of the Aristida-Bouteloua association (Clements, 1920, 144-149) which described the entire Desert Plains Grassland as an association (Weaver and Clements, 1938, p. 525). In everyday practice Clementsians did not always adhere strictly to such formal organization. The faciation tended to fall out except under formal writing and the association--always the real working unit of vegetation, became closely aligned with dominance types.

3 Sacaton and vine mesquite (Panicum obtusum) flats- Flat, mesic (and often saline, sodic, and/or gypyseous) bottomlands, including playas, in the Basin and Range sometimes create unique semidesert grasslands. These constitue range sites (eg.Salty Bottomland, Salty, Gyp in the Trans-Pecos Region), but the collective of such range sites has been recognized as a rangeland cover type. In fact, it appears that there are three appropriate Society for Range Management (Shiflet, 1994) rangeland cover types: Alkali Sacaton-Tobosagrass (SRM 701), Black Grama-Alkali Sacaton (SRM 702) noted above, and Vine Mesquite-Alkali Sacaton (SRM 725). Both of these were listed under Southern Great Plains Cover Types, but that should not be taken too literally as to geography or seen as a precluding technicality. These three plus the Grama-Muhly-Threeawn type (SRM 713) and a semidesert variant of Grama-Bluestem (SRM 714) should have had been listing under Southwestern Cover Types as well as Southern Great Plains Types (Shiflet, 1994 p. v). All three of the "flats" types plus SRM 713 and SRM 714 occur outside the Great Plains and into the Basin and Range physiographic province and its semidesert grassland ranges. The three alkali sacaton types sometimes exists as consociations of vine mesquite or alkali sacaton and as alkali sacaton- Wright's sacaton (Sporobolus wrightii) grasslands. Wright's saqcaton may be locally dominant. On semidesert grassland ranges in Basin and Range physiography the Alkali Sacaton- Tobosagrass cover type is typically a transition between the more saline sacaton flats and the heavier clay tobosa flats. Distinction between SRM 701 and the more "pure" form of tobosagrass swales, the tobosa variant of SRM 505, is often difficult and an arbitrary matter of interpretation.

4. Mixed grass semidesert grassland prairie- This range cover type is probably the third most widespread form of the semidesert grassland following black grama uplands and tobosa swales. It was described by the Society for Range Management (Shiflet, 1994) as the Grama-Muhly-Threeawn (SRM 713). In describing this rangeland cover type Warnock in Shiflet (1994, p. 92) emphasized that while this grassland vegetation had been included as part of the Bouteloua-Hilaria mutica association it had been recognized separately as the Bouteloua-Muhlenbergia-Aristida association even before 1900. Dominant and associate species (and genera) vary widely because this range type developes on habitats varying from bottomlands to ridges with soils ranging from clay loams to gravel. One of the diagnostic characteristics of this type is the absence of tobosagrass except where this vegetation joins tobosa flats. This semidesert grassland range type is unique in that blue grama can dominate on deeper soils in valleys. Panicoid grasses are sometimes represented by cane bluestem and silver bluestem (Andropogon saccharoides= Bothriochloa saccharum).

Species composition, structure, and physiogonomy of this type is such that it "forms a prairie" (Warnock in Shiflet, 1994, p. 92) which is quite distinctive (hence inclusion of "prairie" in the above title by the current author). Likewise, number of grass species is greater in this vegetation than in any other major form or expression of the semidesert grassland (thus the descriptive "mixed grass" in the above title).

5. Sand dunes savanna- This is one of the more restricted forms of semidesert grassland. It includes the Sand Hills range site, but even when stabilized the topography is hummocky sand (duneland) and not of the height or diameter of sand hills per se. This range type is very similar to the "shinnery sands" and has a floristic affinity with it through such species as sand sagebrush (Artemisia filifolia) that contributes to the shrub layer and savanna physiogonomy and grasses like various dropseeds (Sporobolus spp.), little bluestem and, very rarely, giant sandreed (Calamovilfa gigantea). Other shrubs that contribute to the savanna structure and physiogonomy include the ubiquitous honey mesquite (Prosopis glandulosa), longleaf Mormon tea, and Yucca spp.

This sand dune grass-shrub form of semidesert grassland obviously has affinities with the Shinnery Sands ()YOn the example of this climax sand dune range vegetation found and photographed by the author broom was an associate shrub to sand sagebrush. This is a mixed shrub savanna (a grassland with several shrub species), but sand sagebrush was dominant.

This almost striking range cover type was overlooked in the Society for Range Management Rangeland Cover Types (Shiflet, 1994). A Giant Dropseed-Sand Sagebrush or, maybe, just Dropseed-Shrub should be added and described in any future edition of Rangeland Cover Types under Southwestern Cover Types (Shiflet, 1994). There are undoubtedly several variants of this range type, probably with more consistency in dominant grass (Sporobolus) species than in shrubs.

Introduction to 6. 7. and 8: Arrayed in small-scale zonal range communities from basins and plains up hills and mountain foothills there are often three distinctive semidesert grassland types. The lowermost of these is the Chihuhuan Desert-semidesert (Chihuhuan) grassland ecotone, a transition zone between the creosotebush-dominated desert plains and the chino grama-dominated foothill grassland immediately above the ecotone. The chino grama grassland is a counterpart range cover type to the regionally dominant black grama grassland, the major form or type of semidesert grassland, that forms a "patchwork" of vegetation with the Chihuhuan Desertrscrub. The third and highest elevation semidesert grassland type in this zonal "threesome" is the sotol-lechuguilla-grama grassland. Chino grama is generally the dominant (or, at least, most abundant) grass, but sideoats, blue, black, and hairy grama are also common as are the threeawns and cane bluestem. The sotol-lechuguilla-grama grassland is commonly adjacent to and elevationally just below the oak-pinyon-juniper woodland. Chihuhuan Desert-semidesert (Chihuhuan) desert grassland ecotone and sotol-lechuguilla-grama grassland can both be interpreted as savannas (shrub steppes is an apt description for both), but these are nonetheless grasslands.

6. Soto (Dasylirion spp, mostlty D. leiophyllum)-lechuguilla (Agave lechuguilla)-grama grassland- This is the chino (grama)-lechuguilla association of Warnock (1974, p. 47) and the sotol-grassland formation or, simply, sotol grasslands of Wauer (1980, ps. 22-23, 32). Warnock (1974, p. 47) explained that in certain areas this is a black grama-lechuguilla association. Wauer (1980, ps. 22-23, 32) omitted lechuguilla from his vegetation name, but he limited his description and title to the one (admittely a large one) locality of Big Bend National Park. Wauer (1980, p. 28) discussed lechuguilla and described it as being "found almost everywhere on the desert and ranges far up the mountins ..." and "... into the lowlands". It seemed as if Wauer (1980) omitted lechuguilla from his sotol-grasslands because the locally cosmopolitan presence of lechuguilla negated its ecological relevance in designation of a plant community. But since when has that stopped such inclusion when a dominant? If it did, there would be no plant formations, associations, or cover types with "creosotebush" or "mesquite" in their titles!

MacMahon (in Barbour and Billings, 1988, ps. 251-152) considered the D. leiphyllum and Yucca spp. "community type" to be "a transition to grasslands". MacMahon (in Barbour and Billings, 1988, ps. 249-250) interpreted A. lechuguilla to be associated more with the creosotebush-ocotillo-grass savanna of a lower elevation zonal vegetation.

This author observed numerous range plant communities of the lechuguilla-grama association (Warnock, 1974) and the sotol-grassland formation (Wauer, 1980) and found both succulent shrub species present--and typically as co-dominant shrubs-- of the vast majority of these communities. In other of these grass-shrub savanna-like grasslands only one or the other of Dasylirion or Agave species was dominant. Therefore, it appeared logical to use the descriptive designation of sotol-lechuguilla (or vice versa)-grama grassland. Once again the problem of dealing with description and interpretation of grass-shrub vegetation was encountered. Was this a savannah or a grassland range community? Are savanna and grassland mutually exclusive (like desert and grassland) in case of this particular vegetation? How about viewing and designating this range community as a succulent shrub steppe? Or maybe a liliaceous shrub steppe? Even the adjective "liliaceous" is controversial because some plant taxonomists "lump" Agave, Dasylirion, and Yucca in the agave subfamily of the lily family (Liliaceae) while other authors (Powell, 1988) "split" them out into the agave family (Agavaceae).

Vegetation classification can be as controversial as plant taxonomy withthe dilema of "lumping vs. splitting" range or forest communities, but this hillside to foothill grassland community is strikingly different from the black grama and tobosagrass communities of basins and upland plains. The distinctive presence of (shared dominance by) Dasylirion and Agave species at higher elevations and on sloping (often steeply) topography versus widely spaced dispersion of the shrubs Yucca elata and Ephedra trifurca on grama-tobosa grasslands on lower plains and valleys clearly separated the sotol-lechuguilla-grama grasslands from other semidesert grasslands, including the next three semidesert grassland cover types that are also found on hillsides and mountain slopes.

Sotol-lechuguilla-grama grasslands are the highest elevtion semidesert grassland types in the zonal gradations extending from Chihuhuan Desertscrub-semidesert grassland ecotone through chino grama foothill grasslands and ending at lower edges of the oak-pinyon pine-juniper woodland. Mixture and local dominance of grass species, usually one or more of the gramas, changes with elevation as well as with slope and aspect, soil, and overstorey plant species. Sacchuista or bear-grass (Nolina spp.; primarily N. texana and N. erumpens) is also frequently common in this range type, but its presnece in greater amounts (at larger coverage) has been interpreted as indicating some degree of range retrogression due to disturbances like overgrazing and drought.

Somehow the obvious (and very conspicuous) sotol-lechuguilla-grama range cover type that had already been described and named by a trained botanist (Warnock, 1974, p. 47) sin a National Park Service publication (Wauer,1980) was left out of the Society for Range Management(Shiflet, 1994) Rangeland Cover Types . This was an unfortunate and rather glaring omission. Sotol-Lechuguilla-Grama needs to be given formal recognition if there is a second edition.

7. Chino grama foothill grassland- One of the most intriguing of the semidesert grassland range types is one that for whatever reason(s) has been so infrequently described (a local "best-kept secret") and yet is so important in specific rangeland localities. This is apparently due to the fact that the "star of the cast" is an "unsung hero" except at an area scale. Black grama and tobosa are the widely known and highly celebrated featured species of the semidesert grassland. Understandably. They are regional or widespread dominant species. They even have their own entitled rangeland cover types and, as explained above, Clementsian faciation. These two have name recognition and get all the "big billing" along with (though to somewhat lessser degree) the most widely distributed associate species such as sideoats and blue grama and, to the west, Rothrock grama (Bouteloua rothrockii). Even the little runt fluffgrass comes in for its share of the limelight, even if taxonomists change its genus as frequently as their underwear.

But chino grama or, even less revealing, chinograss? Who but the locals ever heard of this one? Yes, the unsung Bouteloua ramosa got due justice in an outstanding regional grass manual (Powell, 2000, ps. 15, 217-217), but this species was often confused with the less valuable, more restricted gyp grama (B. brevisita) including in both of the agrostology encyclopedias of Texas (Silveus, 1933, p. 419; Gould, 1975, p. 351)! For the record, the ever-accurate classic Botany of Western Texas (Coulter, 1891-1894, p. 530) as well as the invincable Warnock (1974, ps 26-27) and meticulous Powell (2000, ps. 216-219) correctly distinguished between these two species based on morphological features and locations. Gyp grama is limited to-- surprise-- gypyseous soils. Those who would know plants must also know the land.

Chino grama frequently forms consociations on rocky foothill ranges similar to those of black grama on upland plains and tobosagrass on swales, but more commonly chino grama is a dominant of mixtures of grasses such as cane bluestem, other gramas, and threeawn species. Chino grama is often co-dominant with black grama to which it seems similar in soil water requirements.Rangemen identifying individual grasss plants on such ranges have to pay careful attention because these two species superficially resenble each other.

Chino grama-dominated grasslands can be almost completely herbaceous or include scattered individuals of woody species including creosotebush, cacti (primarily Opuntia species), Acacia species, ocotillo (Flouquireia splendens), mariola (Parthenium incanum), ceniza (Leucophyllum frutescens), and Big Bend silverleaf (L. minus). In the chino grama grasslands (in contrast to the desertscrub-semidesert grassland transition zone described below) these shrubs are of such exceedingly low density and cover that there is no savannah appearance whatsoever.

Maxwell (1968, ps. 108-109) explained the value of "chino grass", but did not offer a scientific name. Neither did the National Park Service (1983, p. 81) which described it as "the dominant grass of the Big Bend foothills". The restricted range of this type and its defining species were assuredly one reason for lack of appreciation of both.

This slight in recognition included the Society for Range Management publication, Rangeland Cover Types (Shiflet, 1994). If there is a second edition of this reference chino grama-dominated grasslands whould be included. The published cover type could encompass the Chihuhuan Desertscrub-semidesert grassland ecotone described immediately below with both types designated as variants was was done in Shiflet (1994) for a generic black grama-tobosa cover type.

8. Chihuhuan Desert-semidesert (Chihuhuan) grassland ecotone- It was explained above in this introduction that Shreve (1917, 1942), Clements (1920), and Weaver and Clements (1938) regarded much, if not all, of what is today entitled the Chihuhuan Desert (following naming by Shelford, 1942) and much of the semidesert grassland as a transition zone between the Chihuhuan Desert and this grassland.on the eastern edge and between the Sonoran Desert and the grassland on the western boundary of this immense ecotone. The actual nature (climax composition, structure, function, etc.) of this range vegetation remains unclear. The decades-old conundrum is complicated by the mosaic of vegetation characteristic of Basin and Range terrain and by affinity of semidesert grassland to Great Plains grasslands and the occurrence of semidesert grassland to the generally more mesic north and east of the Chihuuhuan Desert.

At local scale there are numerous ecotones (vegetational transition areas) formed when communities of creosotebush (Larrea tridentata)-dominated Chihuhuan Desert on the plains of basins unite with grama-dominated grasslands on bajadas and foothills. Ecotones so formed are relatively narrow corridor-like in shape. These are unique range plant communities that are a composite of lower, generally xeric shrubland and higher, less xeric grassland. Grasses are primarily of cespitose (bunchgrass) form and cresotebush, ocotillo (Flouquieria splendens), and other shrubs grow as individual plants so the general appearance of the plant community is of a savanna. With nearly universal dominance by creosotebush, the regional dominant of Chihuhuan and Sonoran Deserts generally, the savannah could be called a creosotebush shrub steppe.

This ecotonal vegetation is clearly more of a grassland in appearance and, almost surely, in productivity as well given density, cover, and growth of grasses that make up the herbaceous layer.

As was the case for chino grama foothill grassland (the grassland portion of this savanna) and sotol-lechuguilla-grassland this range cover type was not included in Rangeland Cover Types produced by the Society for Range Management (Shifllet, 1994). This oversight should be corrected when and if there is a second edition by addition of the this range type. At least it could be "lumped" in with chino grama foothill grassland (as was done with black grama and tobosagrass) and fall under Southwestern Cover Types.

9. Mixed grass (grama-bluestem-cottontop) hillside grassland- The author used this designation for an array of varied grassland communities, all of which have a "common core" of species, on hillsides and lower mountain slopes. Grassland vegetation appeared to be more diverse in species composition and structure on drier west and south slopes and hillsides.This range cover type encompassed several Soil Conservation Service range sites described within the SCS Desert Grassland vegetation zone including Igneous Hill and Mountain, Limestone Hill and MountainSandstone Hill and Mountain, Foothill Slope, Draw, and Gravelly Hill.

Overall this is the most mesic expression of semidesert grassland. It is one of the most diverse in number of grass species, but extremely consistent in which of these species are present. Sideoats grama and cane bluestem are dominant species on all of these range sites. Arizona cottontop (Trichachne californica), plains bristlegrass (Setaria leucopila), and tanglehead (Heteropogon contortus) appear in almost all of these published range site descriptions. Green sprangletop (Leptochloa dubia) is absent as an associate species only on the drier, more gravelly soils. Black grama is, of course, common to all. Chino grama is essentially absent or appears in only trace amounts on all of these range sites.

This combination of Gramineae species and the absence of chino grama is a unifying basis to a unique grassland community on hill- and low mountain-side habitats.

This is the Bouteloua-Andropogon-Trichachne post-climax community (sideoats grama-feather grass-Arizona cotton grass type) of (Whitfield and Brutner, 1938, ps. 32, 35-36).

Woody species are also diagnostic, but somewhat less consistent in occurrence than grass species. Shrubs are always present even in the climax state. These woody species are also diagnostic, but are more varied among range sites and as to slope and aspect. Mariloa (Parthenium incanum), range ratany (Krameria parvifolia), and Acacia species are key indicator shrubs. The more common cacti are the cholla and tasillo forms of Opuntia (Cylindropuntia subg.) Skeletonleaf goldeneye (Viguiera stenoloba) is also a frequent dominant shrub.

While the sideoats grama-cane bluestem-Arizona cottontop range type develops on hill- and mountain sides it is not typically restricted to elevational zones as are the preceding three semidesert grassland types. Rather the grama-bluestem-cottontop dominated grassland usually develops along entire slopes (or nearly so). It may be that local physiographic features (eg. directional aspect or configurational arrangement of terrain) are determinative in development of this most mesic expression of semidesert grassland.

There is no Society for Range Management (Shiflet, 1994) rangeland cover type for this range type. If there is a second edition of Rangeland Cover Types this vegetation should be described as Grama-Bluestem-Cottontop Shrub under Southwestern Cover Types along with those existing in Shiflet (1994). This range community-- complete with emphasis on grazing use-- was named and described in the literature decades ago (Whitfield and Brutner, 1938, ps. 32, 35-36).

All standard treatments of semidesert grasslands including The Desert Grassland (McClaran and Van Devender (1995), the what-should-have-been-but-was-not comprehensive reference on the subject, limited treatment of the driest grasslands in North America to those of the Chihuhuan and Sonoran Regions of the Basin and Range physiographic province. Semidesert grasslands of the Great Basin Region of the Basin and Range province have either been ignored (eg. McClaran and Van Devender, 1995) or gotten short-shrift treatment. Great Basin semidesert grasslands are much more restricted (less extensive in geographic distribution) and are of relatively less economic importance when compared to the immense extent of Great Basin scrublands, pinyon pine-juniper woodlands, and mountain forests. Regardless, semidesert grasslands of the Great Basin do exist, and these natural grasslands are distinctive from those of the general Chihuhuan-Sonoran zone as well as being economically important (greater grazzing capacity on a unit of land basis relative to most Greatr Basin Desert range). Comprehensive treatment of North American semidesert grasslands deems inclusion of those varied dry grassland cover types.

Coverage of semidesert grassland range herein was divided as to those of 1) Chihuhuan and Sonoran and 2) Great Basin vegetation.

Semidesert grasslands of the more southern portions of the Basin and Range physiographic province developed both as 1) zonal (likely ecotonal) range vegetation between Great Plains grasslands (mixed and shortgrass prairie range types) and the Chihuhuan Desert as well as mountain grasslands and the Sonoran Desert and 2) vegetational mosaics of grassland and among Chihuhuan and Sonoran shrubland (desert). Thus spatial distribution and pattern of Chihuhuan and Sonoran semidesert grassland range varies from broad bands or belts (zonal vegetation occupying relatively large terrestrial space) to "patches" or a "patch-work" dispersed within the overall surrounding desert scrub. The latter spatial arrangement in context of Landscape Ecology consist of semidesert grasland patchs in a desert matrix. It was explained previously that the spatial extent to which Chihuhuan and Desert Desert vegetation has invaded (encroached upon or replaced) pre-Columbian climax semidesert grassland is unknown. Scientific or empirical evidence (research), which has been consistent with anecdotal evidence (eg. land surveyer notes, rancher accounts, explorer and traveler diaries), has conclusively shown that there has been (in some instances continues to be) extensive desertfication and loss of grasslands to scrubland (desert).

There is considerable variation within the Chihuhuan-Sonoran semidesert grassland complex. Unfortunately the extent and kind of this variation, especially as to various grassland communities as reflected in range cover (= dominance) types, was not presented in recent ecological works on the subject as for example in hoped-for encyclopedic coverage in The Desert Grassland (McClaran and Van Devender, 1995).

Technical note: the next five sets of paired photographs compared JPEGs made from 35mm Kodachrome slides by an Epson Perfection V700 Photo color scanner (photographs on left) and a Hewlett-Packard Scan Jet 7400C-Scan Jet XPA color scanning unit (photographs on right). Color was most accurately reproduced by the Epson Perfection V700, but this Epson unit produced (added) an unnatural "sparkle" or "frosted" appearance to the foliage which the Hewlet-Packard Scan Jet 7400C did not add. Conversely, the Hewlet-Packard unit added a bluish-tone to foliage that the Epson did not.

Conclusion: neither the Epson Perfection (perfection it most certainly is not) with its additional "shotgun-shot sparkle" nor the Hewlet-Packard Scan Jet with its added scanned bluish tinge were completely satisfactory for the task of scanning with accurte color. Likewise, both of these cheaply made, imprecise pieces of equipment automatically cropped edges of slides. The only reason that the author used these pieces of "gyp-aggo" apparatus was that they are about all that is available for scanning decades-worth of slides taken prior to introduction of digital imaging (which incidentally has myriad problems of its own as well).

Science (education, in general) alsways involves trades-offs and compromises.

8. Tobosagrass clay flat on an ecotone- A small tobosa swale situated among larger areas of ridges in a transition zone (an "overlap" area) among western Rio Grande Plains, eastern edge of Trans-Pecos Basin and Range, and marginal contact with semiarid Edwards Plateau. There has been inconsistent mapping of vegetational (= land resource) areas of Texas (Gould, 1962, ps. 1, 11; Correll and Johnston, 1979, map 1, ps. 9-10, 12), potential natural vegetation (Kuchler, 1964, map in Garrison et al., 1977), and Texas level III ecoregions (Griffith et al., 2004) with respect to western boundary of Edwards Plateau and eastern boundary of Chihuhuan Desert. This tobosagrass flat and surrounding stand of honey mesquite, huisache (Acacia farnesiana), and Texas persimmon (Diospyros texana) were on range that was included in the western Edwards Plateau by (Gould, 1962, ps. 1, 11; Correll and Johnston, 1979, map 1, ps. 9-10, 12), but in the eastern contacts of Chihuhuan Desert according to (Kuchler, 1964, map in Garrison et al., 1977) and (Griffith et al., 2004). There was not even one single plant of creosotebush (Larrea tridentata) in the range vegetation shown here so designation of this range plant community as being in the Chihuhuan Desert was not overly plausable.

The swale or clay flat supporting a consociation of tobosagrass did provide some textbook examples of this range plant community (even if it was a small parcel of grassland) that was used for instructive purposes (with qualifications duly noted). For practical illustration of the tobosagrass-dominated semidesert grassland the designations of vegetational units were consistent with those cited above. FRES No. 40 (Desert Grasslands Ecosystem). K-48 (Gramagrass-Tobosagrass Prairie). Not specifically described by SRM cover type; variant of SRM 505 (Grama-Tobosa Shrub). Tobosa Grass-Scrub Series of Brown et al. (1998). Level III ecoregion of Texas was transition between Chihuhuan Deserts and Playas Ecoregion 24a of Chihuhuan Deserts and Semiarid Edwards Bajada Ecoregion 31b of South Texas Plains (Griffith et al., 2004).

Val Verde County, Texas. October, phenological stage of tobosa varied from anthesis through grain-ripe to grain-shatter.

9. "And the green grass grew all around, all around; and the green grass grew all around" (American folk song)- Characteristic sward of tobosagrass on a swale showing the semi-cespitose habit of this rhizomatous perennial eragrostoid grass. Individual plants of tobosagrass typically grow in close proximity to each other so as to form an open sod or turf, especially on more mesic habitats (eg. swales and larger bottomland sites), so that stands of tobosa have a bunchgrass-like appearance. This is in contrast to the "kissin' cousin", curly mesquite (H. belangeri), which is stoloniferous and forms a more nearly closed turf or complete sod.

This small stand or consociation had been lightly grazed by cattle such that individual plants and the open sod or turf were more obvious. These photographs were "picture perfect" examples of proper degree of use, which in the semiaridity or aridity of this range environment was on the light side of moderate. This range professor reminded his student readers that moderate grazing (= defoliation) is not automatically synonymous with proper grazing any more than is light or heavy degree of grazing defoliation proper or improper. Proper use factors are not only species-specific, but even site-specific for species-specific standards or guidelines. A key diagnostic guide to proper degree of use (the first and usually the most important of the Four Cardinal Principles of Range Management) is presence of individual shoots that were ungrazed and, usually, matured to flowering and grain production. Reproduction of perennial grasses like tobosa is usually asexual (by tillers and rhizomes in H. mutica) so seed production is not necessary nor usually important for regeneration of this valuable climax species (decreaser on swale sites). Rather, presence of sexually reproductive shoots is a very good sign to graziers that the tobosagrass range was properly managed as to degree of use. Plus, this degree of grazing defoliation with subsequent seed-set best provided for the option of establishment of seedlings that can fill in interspaces among existing tufts of older plants. Seedling establishment permitted presence of new genotypes (the opportunity for on-going genetic adaptation) of this remarkable and valuable semidesert species.

Val Verde County, Texas. October, phenological stage of tobosa varied from anthesis through grain-ripe to grain-shatter. FRES No. 40 (Desert Grasslands Ecosystem). K-48 (Gramagrass-Tobosagrass Prairie). Not specifically described by SRM cover type; variant of SRM 505 (Grama-Tobosa Shrub) variant. Tobosa Grass-Scrub Series of Brown et al. (1998). Level III ecoregion of Texas was transition between Chihuhuan Deserts and Playas Ecoregion 24a of Chihuhuan Deserts and Semiarid Edwards Bajada Ecoregion 31b of South Texas Plains (Griffith et al., 2004).

10. Beautiful, and outstanding example to boot- Individual plant of tobosagrass that was grazed during current growing season to proper degree of use as determined by general qualitative appearance, but not on specific quantitative guidelines (assuming that such even exist). Key features of proper grazing included: 1) adequate photosynthetic tissue (both leaves and culms) remaining following grazing, 2) some shoots that were permitted to mature to sexually reproductive (= flowering) stage, 3) irregular, domed shape of grazed plant rather than a heavily cropped one having a flat, highly hedged appearance, and 4) overall degree of utilization (composite of defoliation for whole plant) that was somewhat on light (conservative) side of the total or maximum utilization that would enable the plant to survive. In regards feature #4, management of this tobosagrass range was such that some "surplus" feed was left for an emergency, risk, etc. that might befall plant, animal, or ranching firm. The conservative or cautious grazing use would come closer to permitting higher levels of herbage production under environment stress, especially drought. The rangeman responsible for husbandry of this range had hedged his bets and left "a little extra" grass just in case "things get tight". Such wise stewartship is good ranch as well as good range management.

The rest of the explanation for the bountiful flowering of tobosa on this range as shown in these photographs was an extremely wet late summer and early autumn. Numerous, well-spaced showers and cool temperatures resulted in near ideal soil moisture conditions. Students take note: even abundant rainfall and other features of a fabulous plant-growing environment would not have permitted the profuse flowering and lush foliage of this tobosagrass had it been grubbed to the ground by overuse. Vice versa, even if growing conditions had been adverse for tobosa on this swale there would still have been some sexual reproduction in the stand given the wise use management--especially proper degree of utilization--it received.

Val Verde County, Texas. October, phenology ranged from anthesis to grain-shatter stages.

11. Nothing much purtier to a desert grassman- A large speciment of tobosagrass at peak bloom on a swale in Rio Grande Plains savanna-Chihuhuan Desert ecotone. This plant had been properly grazed (defoliation of outer edge of grass still evident in foreground) and, with blessings of late-growing season rain showers, a high number of shoots had developed to sexual maturity.

Val Verde County, Texas. October. On this one plant phenological stage varied from anthesis through grain-ripe to grain-shatter (with more soil water from each new shower ever more shoots advanced to flowering stage).

14. Ring muhly or ringgrass (Muhlenbergia torreyi)- This cespitose grass grows on plains and mesa grasslands of the Great Plains through the semidesert plains grasslands of the Trans Pecos Basin and Range province. As indicated by it's common name ring muhly exhibits a unique growth habit. This bunchgrass produces secondary shoots only in the form of tillers such that asexual reproduction takes place around edges of the existing mother plant. The result is an ever-expanding circular pattern of growth. When the oldest tillers (mother and first daughter shoots) that were in the center of the plant were shed (ollowing their senescence and death) the result was a "ring" of tillers. Ring muhly shoots often have characteristically curled leaves.

Ring muhly is a common but not a major forage-producing species. It is, however, often readily taken by livestock. Ringgrass is undoubtedly valuable for erosion control and watershed protection. It's growth pattern was an apt illustration of the concept of clonal organism.

Black grama semidesert grassland in "mint condition"- With proper management-- in this case, limited to proper grazing management--even after a decade or more of severe drouth this vegetation was still as virgin as it gets. Species composition, community structure, and ecosystem function was the same as if human eyes had never rested on it. This was almost a single grass species-community with sparsely scattered evergreen shrubs. There were also scattered individual plants of sideoats grama (like the larger cexpitose grass plant in center foreground) and cane bluestem. Tobosagrass grew on the isolated microsites of small depressions in the land surface.

Students were again reminded that black grama semidesert grassland is by far the most common kind or form of what has traditionally been called "desert grassland. Black grama is the regional or zonal dominant grass of the greater Chihuhuan-Sonoran Deserts Basin and Range Region.

Presidio County, Texas. June, early estival aspect prior to onset of summer rains. FRES No. 40 (Desert Grasslands Ecosystem). K-48 (Grama-Tobosa Prairie). SRM 505 (Grama-Tobosa Shrub). Grama Grass-Shrub Series of Brown et al. (1998). Chihuhuan Deserts- Chihuhuan Desert Grasslands Ecoregion, 24 b (Griffith et al., 2004).

Species diversity on "perfect" black grama semidesert grassland- Species diversity on the black grama form or expression of semidesert grassland is typically very low. It is a classic Clementsian consociation across vast areas. Other grass (and a few forb) species are present, but in small to almost trace amounts. Two of the more frequent of associate grass species include sideoats grama--State Grass of Texas--, which was conspicouosly dominant locally in the foreground, and cane bluestem, the conspicuous, somewhat decumbent grass with larger shoots in center midground. Both sideoats and cane bluestem are mid-grasss species (in contrast to shortgrass species like black, hairy, and blue grama). Given presence of both mid- and shortgrasses this range vegetation could be described precisely as "mixed prairie", but that designation as a proper title has usually been reserved for Great Plains grassland communities that also often include tallgrass species. Kuchler (1964, in Garrison et al., 1977) entitled this range type "prairie". It fits.

"Savannah" would be another arbitrary distinction that could be used to describe this range vegetation, specifically to characterize for instructive purposes presence of woody plants (the larger of which have a tree-like form). In this author's judgment, semidesert grassland is-- as historically described by the word "grassland"-- a true grassland (ie. vegetation and a range cover type in the grassland biome). Dick-Peddie (1993, p. 107) cited other workers who described this vegetation as a "shrub-steppe" . It is important for those new to this range vegetation to understand that presence of the soaptree yucca so prominent in this photograph and longleaf joint-fir or longleaf Mormon tea (Ephedra trifurca) are indicator and defining species to climax black grama semidesert grassland. Dick- Peddie (1993, ps.116 ) carefully explained this key floristic feature. That key botanical phenomenon was underscored here and now by the current author as well.

Presidio, County, Texas, early estival aspect prior to convectional summer rains. FRES 40 (Desert Grasslands Ecosystem). K-48 (Grama-Tobosa Prairie). SRM 505 (Grama-Tobosa Shrub). Grama Grass-Shrub Series of Brown et al. (1998). Chihuhuan Deserts- Chihuhuan Desert Grasslands Ecoregion, 24b (Griffith et al., 2004).

Black grama-dominated semidesert prairie- Soaptree yucca, State Flower of New Mexico, is an indicator of climax semidesert grassland of the black grama form (Dick-Peddie, 1993, ps. 131-132) and presents a savanna-like physiogonomy to this wonderfully adapted range vegetation. The semi-open sward seen in this and the next photograph is also a obvious physionomic characteristic of semidesert grassland, especially of the black grama form. As shown in photographs below, black grama, like tobosagrass, spreads (often vigerously and extensively) by stolons. The semiaridity of climate and xeric nature of soils is such that the soil surface is not covered to the extent that it is in more mesic areas and with other stoloniferous species like buffalograss (Buchloe dactyloides) or even the larger rhizomatous bunchgrasses. Buffalograss, blue grama, bush muhly, mesa dropseed, and perennial threeawns are typically present even on virgin state black grama range like this one, but their overall density and cover is miniscule other than at microsite scale. A high percentage of these grass species (eg. bush muhly, mesa dropseed, and threeawns) are strictly cespitose and produce no stolons.

Presidio County, Texas. June, early estival aspect (prior to summer rains necessary for meaningful "green-up"). FRES No. 40 (Desert Grasslands Ecosytem). K-48 (Grama-Tobosa Prairie). SRM 505 (Grama-Tobosa Shrub). Grama Grass-Shrub Series of Brown et al. (1998). Chihuhuan Deserts- Chihuhuan Desert Grasslands Ecoregion, 24b (Griffith et al., 2004).

Overall appearance of black grama-dominated semidesert grassland range- This climax vegetation illustrated physiogonomy and botanical compostion produced by presence of both herbacesou and woody species. In addition to soaptree yucca, longleaf Mormon tea or joint-fir was prsent in this slide. The herbaceous layer was "pure" black grama and the sward had the patchy or spotty appearance produced by this species. (Even though black grama reproduces to large degree via stolons this species still creates a semi-open herbaceous canopy.)

Dick Peddie (1993, ps. 116, 131-132) explained that presence of certain diagonostic (= indicator) species on what was Chihuhuan Desertscrub provided evidence that the vegetation had been semidesert grassland which had most likely been converted to desert by human-induced shifts in vegetation. Indicator species included longleaf Mormon tea (in contrast Torrey Mormon tea [Ephedra torreyana]), desert holly, and fluffgrass (Triens pulchellus). Presence of both soaptree yucca and Mormon tea added another layer to this range plant community and resulted in rang vegetation that had a savanna-like appearance and a shrub-steppe physiogonomy. These evergreen, narrow-leaved shrubs also produced a unique visual aspect to the vegetation.

Presidio County, Texas. June, early estival aspect (prior to onset of summer rainy season). FRES No.40 (Desert Grasslands Ecosystem). K-48 (Grama-Tobosa Prairie). SRM 505 (Grama-Tobosa Shrub). Grama Grass-Shrub Series of Brown et al. (1998). Chihuhuan Deserts- Chihuhuan Desert Grasslands Ecoregion, 24b (Griffith et al., 2004).

18. Sward of black grama (Bouteloua eriopoda) - Outward physical appearance of a sample of a stand (= a colony might be more appropriate) of black grama. On a lightly grazed (by cattle) range that was in Excellent range condition class at the end of first growing season following the Long Drought of the 1990s through early 2000s. Many of the eragrostoid (= chloroid) grass species (those in Gramineae subfamily, Eragrostoideae) have shoots that live for more than one growing season (ie. have aboveground living tissue that persists for two or more years). This is not to be confused with the biennial life cycle (they are perennial species) or with semi-woody (either suffrutescent or becoming woody) plants. Rather, some shoots of some of these grasses under certain growing conditions simply do not die completely and instead maintain some meristematic tissue in culms or buds. Plants of certain grass species enter (or persist) into a condition that might be described as "semi-dormancy" from which they are able to emerge and (or in which they) "green-up" (ie. produce new tissue that is soon capable of photosynthetsis). This is undoubtedly an evolved opportunistic adaptation for survival under sporadic growing conditions such as aridity, periodic heavy precipitation, widely fluctuating temperatures, etc.

Plants in such a state of "suspended perenniality" (to coin a purely descriptively instructive term) not only respond quickly to episodes that are favorable for growth and/or reproduction, they also retain biomass of higher nutritive value (in contrast to the nutritionally leached herbage of plants and species that do not maintan such tissue and instead "die back to the ground" at the end of each growing period. This is a major reason why available herbage of most panicoid grasses like Andropogon, Bothriochloa, Panicum, and Paspalum species is less nutritions and palatable than that of of some eragrostoid grasses like certain species in Bouteloua, Chloris, and Spartina. Biomass of buffalograss also falls in this latter group.

The phenomenon just described can be visually observed by the "looks sorta green" (pale or "dim" green or gray-green) color of shoots of these species (again, at least under certain conditions). This condition and coloration was readily seen in the black grama shoots shown in this slide. Even though summer rains had not commenced at time of photographing these plant there was enough residual soil moisture (from winter and spring precipitation) that lower parts of last year's shoots were still partly green. This plus new growth of this year's young shoots provided the coloration shown here. (This is another reason for using non- or low-color enhancing film or neutral film like Kodachrome.)

Students should also take note of the open appearance of black grama sward. Black grama is not a cespitose (bunchgrass) species. Instead it is stoloniferous and a sod-forming grass. Black grama reproduces asexuallly by tillers as well as stolons but the resultant growth pattern and appearance is of an open or patchy sod with substantial bare soil among dense "clumps" of a perennial grass that spreads most effectively by runners (stolons).

19. Plant of black grama or wooly grama- This "plant" of black grama consist of a larger "clump" (group of tillers) behind three smaller "clumps". The three smaller "bunches" are clones or modules ("daughter plants") produced asexually from the larger "parent" (or "mother") plant, the latter of which was almost undoubtedly a "daughter plant" from its "parent plant". Assuming that the "parent" of the "daughter plants" was itself a clone or module of a preceding parent, each of these vegetatively or asexually produced "plants" (each module) was a ramet of one genet, the original genetic (sexual) individual. This illustrated a modular organism. Only the genet, the plant produced by sexual reproduction (exchange of gametes) was a unique or "one-of-a-kind" organism. How many years, decades, or, even, centuries ago this sexually generated ancestor came into existence is known but to God.

Black grama reproduces by seed (from a caryopsis) very rarely. Prof. Ken A. Valentine spent over forty years involved in research on the Jornada Experimental Range and New Mexico State University College Ranch. Valentine (personal communication) claimed that he had never seen a single black grama seedling.

Presidio County, Texas June.

20. Shoots of black grama- Another common name for Bouteloua eriopoda is wooly grama. This basis for this descriptive name was the abundant pubescence on the internodes (hence, wooly or fuzzy stems). This pubescence and a unique shade of green color on the culms is the distinctive idenfiying feature of this regional dominant and extremely valuable range plant.

Big Bend Ranch State Park, Presidio County, Texas. June.

21. Detail of black or wooly grama shoot- Some sheaths on black grama shoots cover (enclose) almost all of the internode of the culm. While rangemen refer to the wooly "stem" of wooly grama it is actually the wooly leaf. Leaves are frequently absent or missing from portions of black grama shoots thus exposing the culm that is often a light yellow color. This alternating green and yellow color pattern was visible in the preceding slide. Interspersed with the green and yellow pattern of living shoots is the dull gray color of dead-but-still-attached shoots like the one featured in this shot. This shoot was a tiller, a vertical or upright intravaginated shoot.

Presidio County, Texas. June.

22. Black grama runners- In contrast to the tiller in the preceding photograph, a runner (stolon is the scientific term) is a horizonal extravaginated shoot. In this photograph two stolons were laying atop and across a third (though less visible) stolon. All three stolons were living, but as is often the case for shoots of this species they looked "more dead than alive". Three nodes with emerging new clones or modules (appearing as buds) were visible. Plants were just initiating new growth at onset of summer rainy period.

Presidio County, Texas. June.

23. "Throw out the life line"- True to the words of the old hymn by E.S. Ufford black grama has grown the life line for another generation of this mostly clonally reproducing mainstay of the semidesert grassland ranges. Several stolons were visible on the surface of this sandy semidesert soil. A large module or ramet was developing from the node of the foremost runner. This "daughter plant" was shown in more detail in the second slide.

Presidio County, Texas. June.

24. "Putting down roots" or "a hen and two chicks"- Two stolons from an established black grama plant have each produced a "new plant" (a module= clone= ramet). Each "daughter plant" became established (one or maybe two growing seasons prior) and was waiting for rain at beginning of the summer rainfall period. Summer is when most precipitation occurs in the climate of the Trans-Pecos Basin and Range.

New modules were developing on another stolon (to left of established ramets) to be ready for next summer's rain.To a range plant and a rangeman, "There's always next year". The asexual reproduction shown here took place during last phases or just after one of the most severe droughts in weather records. Grazing management must allow for such reproduction: "Take care of the grass and it will take care of you".

Presidio County, Texas. June.

25. Inflorescences of black or wooly grama- The infloresecence type of eragrostoid grasses (those in subfamily, Eragrostoideae) is a raceme. Spikelets are borne on pedicels on the rachis (adjective, pedicellate). That black grama produces grain was shown here; that such grain is less productive of new black grama plants was shown in preceding photographs of asexual reproduction.

Presidio County, Texas. June. (Spikelets had persisted on the rachis throughout course of winter and spring suggesting to any range-wise rangeman that there had been but scant precipitation.)

26. Mesa dropseed (Sporobolus flexuosus)- Local stand of mesa dropseed. This is one of the most common and important species on recovering black grama range (deteriorated range undergoing plant succession). Mesa dropseed appears to respond to disturbance primarily as an increaser (Pieper and Beck,1990), but on many, if not most, range sites in the semidesert grasslandmesa dropseed is an important component of the climax range vegetation (Soil Conservation Service, undated; range site descriptions). Mesa dropseed is especially important on depleted black grama range that was converted into Chihuhuan Desertscrub disclimax. On such "man-made" deserts mesa dropseed may be a major grass species along with the less palatable perennial threeawns and the palatable bush muhly which frequently grows near creosotebush.

Elephant Mountain Wildlife Management Area, Brewster County, Texas. June, early new growth ("green-up") at beginning of summer rainy period.

27. Individual plant of mesa dropseed- Specimen of mesa dropseed with the "sprawling" habit frequently developed in this species. The twisted or rolled leaves are a common characteristic of Sporobolus species. The grass's "next door neighbor" was the invasive, but short-lived suffrutescent composite, broom snakeweed.

New Mexico State University College Ranch, Dona Ana County, New Mexico. June, early new growth ("green-up") at onset of summer rainy period (dead plant material was biomass produced the previous summer).

28. Mesa dropseed (Sporobolu;s flexuosus)- Whole plant--shoots; aboveground portion-- of mesa dropseed (first slide) and details of shoots (second slide) of mesa dropseed, the principal increaser on many degrated former black grama-dominated semidesert grassland ranges. All conspicuous plant parts (all but small green basal and the few green adult leaves) were produced the preceding summer-fall growing season. The bent or flexuous leaves are a feature common to most Sporobolus species, but apparently they were so prominent in this specific species as to serve as basis for the specifid epithet.

The deep sandy soil of this mesa dropseed specimen probably was the edaphic basis of a black grama semidesert grassland ecosystem that was largely replaced by the adjacent but distinct Chihuhuan Desert due to human action. This location was directly on the El Camino Real, the first European road in North America (ran from Santa Fe to Chihuhua City). Grazing by draft animals (horses, mules, asses, oxen) used for trade and travel along this route for nearly 300 years was the most probable cause of human-induced desertification.

On such drastically altered landscapes and ecosystems mesa dropseed is a keystone species, and the key to whatever recovery of vegetation, soil etc. is possible.

New Mexico State University College Ranch, Dona Ana County, New Mexico. June, plant organs were of both the previous growing season and the first part of current growing season.

29. Local stand of sixweeks grama (Bouteloua barbata)- On this spot (microhabitat) several plants of the ephemeral sixweeks grama had germinated and just completed their short life cycle. Sixweeks grama is one of the few annual grass species that is native to semidesert grassland and desertscrub in the Chihuhuan Region. Perenniality is a major plant adaptation to harsh environments like desert, alpine, saline, and rocky ecosystems. Under severe disturbance (eg. anthropogenic causes that highly modify natural habitats) plant species with the annual life cycle pattern become more competitive with those having biennial and perennial life cycles. This is the concept of therophytes. Therophyte refers to one of Raunkiaer's life form groups that has the annual or ephemeral life cycle so that growth and sexual reproduction are completed quickly during short periods when conditions are favorable and that then survive unfavorable periods as seed or fruit.Therophytes are typical of deserts, especially disturbed desert habitats, tilled land, and overgrazed pastures. The seed or fruit is the plant organ most capable of surviving severe stresses like extreme temperatures, dryness, and long periods of dormancy. Therophytes are usually pioneer species on severely disturbed land. This initial repopulation of plants is essential to plant succession to facilitate invasion and establishment of plant species of higher successional order. Facilitation is the contemporary term for the preceding synonymous term of reaction proposed by F.E. Clements.

On almost all overgrazed ranges of about every range type annual plants become more plentiful with continuing retrogression, the retrograde movement of a biotic community toward communities of lower succeessional order (= lower seral stages). With continuing retrogression annual or ephemeral species often become community dominants. The sixweeks grama plants shown here were growing on land that had been a main trail along El Camino Real, the oldest European road in North America, that had been subjected to about every human activity imaginable, not least of which was livestock grazing. Climax dominants like black grama and tobosagrass were displaced by plant species of lower successional order as range retrogression moved climax black grama semidesert grassland to anthropogenic Chihuhuan Desert. The rangeland at this location is at static or maybe upward range trend as human disturbance has been reduced or eliminated. Sixweeks grama was doing "yeoman's service" to improve the range.

Under such successional conditions annual and ephemeral species-- at least native species-- are not weeds. They are essential for healing of the range. Ephemerals and annuals are as ecological invaders because they do invade and colonize disturbed rangeland. The diagnostic successional designation of invader does not always imply noxious plant. Yes, under many conditions invader certainly may mean weed or brush, but when the impacts of invaders are those of beneficial reaction (= facilitation) benefits of invaders exceed their adverse impacts. If such ephemerals are weeds they are virtuous ones.

Ephemeral in this usage refers to annual plant species that have especially short life cycles.Ephemeral grasses are often called "sixweeks grasses". Another "sixweeks grass" that is native to the semidesert grassland range type is sixweeks threeawn (Aristida adscensionis). It is usually less common than sixweeks grama on sandy soils.

New Mexico State University College Ranch, Dona Ana County, New Mexico. June, seed-shattter stage of phenology.

30. Sixweeks grama (Bouteloua barbata)- Example of one of the most common ephemeral grasses on degraded semidesert grassland and Chihuhuan Desert ranges. This specimen had just had its moment in the sun: it recently completed its short life cycle culminating with shedding of grain. It had achieved the ultimate biloogical success: it reproduced and propagated its kind. The amber color of these plants (captured by ever-true color Kodachrome) is typical of most annual grasses.

On an old trail of El Camino Real, New Mexico State University College Ranch. Dona Ana County, New Mexico.June, seed-shatter phenological stage.

31. Bush muhly or hoe grass (Muhlenbergia porteri)- Along with black grama, bush muhly is one of the most palatable--hence most apt to be grazed out--climax grass species of the semidesert grasslands. In western, more xeric areas of the Chihuhuan Region bush muhly is an associate to black grama. Bush muhly is frequently observed to grow in association with and even outcompete creosotebush on the Chihuhuan Desert-semidesert (Chihuhuan) grassland ecotone. The phenomenon (complete with photograph) was described in the Chihuhuan Desert chapter herein. Powell (2000, p. 177) stated that the common name of bush muhly was derived from the association of this palatable species with protection-providing shrubs. That is logical, but the bush-resembling general appearance of this grass would also seem a likely origin of the adjective, "bush". Whitfield and Anderson (1938, p. 174) stated that bush muhly "... forms bush-like masses". Whitfield and Anderson (1938, p. 174), Gould (1951, p. 201-202), and Humphrey (1960. ps. 67-69) remarked that in the origina range vegetation (prior to advent of ranching) bush muhly was extremely abundant, but that th