The Rio Grande (Tamaulipan) Plains has traditionally been interpreted by Texas workers as one of the state's vegetational (= land resource) areas. Some of Texas' vegetational areas like the Pineywoods, Blackland Prairies, Coastal Prairies and Marshes, and Post Oak Savanna were based on vegetation. Other land resource areas including the High Plains, Rolling Plains, Edwards Plateau, Trans-Pecos Basin and Range, and Rio Grande Plains were based on general--and often popularized--notions of geology, especially physiographic provinces and units thereof0. The land resource or vegetational area of Rio Grande Plains or, sometimes, South Texas Plains (as well as the whole Tamaulipan unit which also includes land in Mexico) is strictly speaking part of the West Gulf Coastal Plain physiographic province (Feneenman, 1938, ps. 100-120). The West Gulf Coastal Plain province extends to the Balcones Escarpment so that a clear delination exist between the Coastal Plain and the southeastern portion of the Edwards Plateau (which is in Great Plains physiographic province). Other distinctions between the Rio Grande Plains and other land resource or vegetational areas cannot be drawn so easily from physiographic provinces. The Lampasas Cut Plain, Grand Prairie, CrossTimbers, Blackland Prairie, and Pineywoods are also in the Western Gulf Coastal Plain.

As such, criteria for distinctions among and within vegetational areas must include (also on basis of definition) the key criterion of vegetation. Even the inclusion of and definition as to vegetation does not handily or readily define the Rio Grande Plains because vegetation of this designated area is considerably diverse. Even at larger-than-local spatial scale native plant communities of the Rio Grande Plains include several map units of natural vegetation (Kuchler, 1964; Kuchler in Garrison et al., 1977) as well as smaller vegetational units too small and scattered to be mapped conveniently. There are, of course, always arbitrary aspects to designation and description of vegetation not to mention objectives of, disciplinary perspectives of , and value judgments in Vegetation Science.

The physiographic province of Western Gulf Coastal Plain has geologic variables that further confound description and classification of natural vegetation in the Rio Grande Plains even over relatively small mapping space. The southern apex of this vegetational area includes the Rio Grande Embayment (Fenneman, 1938, p. 102) which is distinct from the rest of South Texas Plains.

Historically, the Rio Grande Plains of Texas has been interpreted as including the mesquite-acacia savanna (Andropogon-Setaria-Prosopis- Acacia), mesquite-live oak savanna (Andropogon- Prosopis-Quercus), and ceniza shrub (Leucophyllum-Larrea-Prosopis) designated in the USDA Forest Service version of Kuchler units of Potential Natural Vegetation (Garrison et al., 1977) as numbers 54, 55, and 38, respectively. Additionally, there are various forms of gallary and floodplain forests along the Rio Grande that are too small or local for mapping units of the size used by Kuchler (1964, in Garrison et al., 1977) but that are nonetheless forest cover (hence, range) types.

Range types of the Rio Grande Plains were treated below based on the "units of vegetation" or the "physiogonomic types" (Kuchler, 1964, p. 3) recognized by Garrison et al. (1977) and as consistent as possible with rangeland cover types described by the Society for Range Management (Schiflet, 1994) and forest cover types recognized by the Society of American Foresters (Eyre, 1980).

The South Texas Chaparral or Rio Grande Plains "brush country"-- Texas-Tamaulipan Thornscrub Ecoregion 31c; Kuchler No. 54 (Mesquite-Acacia Savanna) -- is remarkably diverse with several range subtypes and numerous range sites, notwithstanding the monotous appearance of a mostly brush-infested landscape. Apparent homogenity of general appearance (physiogonomy and structure) of the south Texas shrubland may be a reason why the Society for Range Mangement (Shiflet, 1994) described only the Mesquite-Granjeno-Acacia rangeland cover type (SRM 728) for this farflung range area. (Another reason for this paucity of cover type titles and descriptions is likely that nobody saw fit to "write them up" or submit them for incluision in the official societal publication.) Nonetheless, there are many different range plant communities that comprise Rio Grande Plains range vegetation.

Many (probably most) of these range types, including some subtypes and variants of SRM 728, are disturbance climax types. This fact alone allows for essentially limitless variations in range vegetation. There are, however, undoubtedly other range cover types that are climax vegetation especially when interpreted from the Tanslian polyclimax perspective. This includes cover types (or, probably the most precise designation, subtypes) within what has been called generally the "mixed brush type".

Two of the more common forms, types, or, according to Scifres (1980, p. 32), subtypes of Rio Grande Plains shrublands (South Texas Chaparral) are: 1) guanjillo-ridges and mixed-brush uplands and 2) hardlands vegetation (Scifres, 1980, ps. 32-34). Examples of these two range cover types (= subtypes) were given immediately below.

8. The following four photographs of range vegetation portrayed the typical guajillo ridges and mixed brush uplands type (= subtype) of the generic "mixed brush type" of the South Texas Chaparral. Scifres (1980, ps. 32-33) described this rangeland vegetation as comprised of "almost pure stands" of guajillo on shallow, stoney soils like gravelly ridges or rock outcrops with downslope gradations of vegetation into various range communities distinguished and dominated by various Acacia species such as twisted acacia and blackbrush as well as honey mesquite, granjeno or spiny hackberry, and lotebush along with less common species including Berlandier wolfberry, javelina bush (Condalia ericoides= Microrhamnus ericoides), cenizo (Leucophyllum frutescens), agarito (Berberis trifoliolata= Mahonia trifoliolata), Yucca spp., and whitebrush or beebush (Aloysia lycioides= A. ligustrina= A. gratissima= Lippia lycioides), the latter of which often forms "dense, almost pure stnnds" on deeper, more fertile soils like those of bottomlands.

Some of the most common grasses included Chloris and Paspalum species (Scifres, 1980, p. 31). Thomas (in Gould, 1962, p. 11) listed genera and, less commonly, species of grasses as to sandy loam, clay and clay loam, and saline soils. Gould (1975, p. 11) more or less followed the descriptions of Thomas (in Gould, 1962) but in even more abbreviated form. Based on usually brief reference accounts by various authors it appeared that grasses on range types and sites of the Rio Grande Plains brush ranges were less distinctive and diagnostic than major woody species.

"Conspicuous by their absence" (rarity would be a more precise description) were honey mesquite and huisache, the sterotypic dominants over much of the "brush country" of the Rio Grande Plains. In fact, the remarkable rarity of these two ubiquous woody legumes strongly suggsted that this was not an example of the typical brush-infested deteriorated range. Dominance by guajillo and cenizo was consistent with relative scarcity of mesquite and huisache and with the description cited above from Scifres (1980, ps. 32-34) in which it was concluded that "... the vegetation, even before the coming of of the white man, was low-growing brush of a variety of species" though "...such low-growing woody plants have increased in density with the activities of civilization (Scifres, 1980, p. 32)..

Guajillo-mixed brush uplands- On this stoney ridge-sandy loam soil habitat a mixed shrub form of South Texas Chaparral was co-dominated by guajillo and cenizo (dark-green, compound-leafed shrub at right and grey or silvery shrub at left background, respectively). Major associate species was whitebrush (light-brown, largely leafless shrub in foreground), but also present was broom snakeweed (Gutierrezia sarthrae), Torrey croton (Croton torreyanus= C. incanus). Grasses were very sparse. Most common Gramineae species were shortspike windmillgrass (Chloris subdolichostachya) and silver bluestem. The most common forb was the annual species Texas croton or tinajera (Croton texensis).

Live Oak County, Texas. October, autumnal aspect. FRES No. 32 (Texas Savanna Shrubland Ecosystem). K-54 (Mesquite-Acacia Savanna). SRM 728 (Mesquite-Granjeno-Acacia). Mixed Deciduous Series of Tamaulipan Thornscrub subdivision (biotic community) of Brown et al. (1998). Southern Texas Plains- Texas-Tamaulipan Thornscrub Ecoregion 31c (Griffith et al., 2004).

A diverse brush patch- Another view of range vegetation in the example of the guajillo ridges and mixed brush uplands subtype presented in the preceding slide. In addition to guajillo, cenizo, whitebrush, broom snakeweed, and Torrey croton visible in that photograph, this sample included Spanish dagger, Texas persimmon (Diospyros texana), and agarito. Cover and density of grass species were also greater than in the "photo-plot" of the preceding slide.

Live Oak County, Texas. October, autumnal aspect. FRES No. 32 (Texas Savanna Shrubland Ecosystem). K-54 (Mesquite-Acacia Savanna). SRM 728 (Mesquite-Granjeno-Acacia). Mixed Deciduous Series of Tamaulipan Thornscrub subdivision (biotic community) of Brown et al. (1998). Southern Texas Plains- Texas-Tamaulipan Thornscrub Ecoregion 31c (Griffith et al., 2004).

Chaparral thicket in South Texas Plains- This third view of range vegetation on a guajillo ridges and mixed brush upland subtype "sported" more of the conspicuous Texas persimmon (shrubs with white-barked trunks or shoots) along with guajillo, cenizo, whitebrush, Torrey croton, agarito plus some blackbrush and granjeno or spiny hackberry, and shrubby blue sage (Salvia ballotrifolia). The most common grasses (and these were "few and far between") were silver bluestem and shortspike windmillgrass. Potential grass species were those that were present in strips of grassland vegetation maintained by mechanical treatment which was presented in the immediately succeeding photograph.

Live Oak County, Texas. October, autumnal aspect. FRES No. 32 (Texas Savanna Shrubland Ecosystem). K-54 (Mesquite-Acacia Savanna). SRM 728 (Mesquite-Granjeno-Acacia). Mixed Deciduous Series of Tamaulipan Thornscrub biotic community (Brown et al., 1998). Southern Texas Plains- Texas-Tamaulipan Thornscrub Ecoregion 31c (Griffith et al., 2004).

Will the real Rio Grande Plains savanna vegetation "please stand up"?- A swath through an otherwise dense stand of shrubs on a guajillio ridge-mixed brush uplands range type had been maintained by shredding (mechanical control by use of shredder or rotary mower). Was the mechanically maintained grassland or the otherwise-present shrubland the real climax vegetation. Or was climax (= potential natural vegetation) a savanna of varying plant community structure but of a botanical composition made up of all native species (woody and hebvaceous species)?

Dominant grasses in the swath of grassland were shortspike windmillgrass and silver bluestem. Also present was little bluestem, perennial threeawns of the Aristid purpurea complex, buffalograss, curly mesquite, reverchon bristlegrass (Setaria reverchonnii), plains bristlegrass (S. leucopila), hairyseed paspalum (Paspalum publiflorum), and, rarely, tanglehead (Heterpogon contortus).

Live Oak County, Texas. October, autumnal aspect. FRES No. 32 (Texas Savanna Shrubland Ecosystem). K-54 (Mesquite-Acacia Savanna). SRM 728 (Mesquite-Granjeno-Acacia). Mixed Deciduous Series of Tamaulipan Thornscrub biotic community (Brown et al., 1998). Southern Texas Plains- Texas-Tamaulipan Thornscrub Ecoregion 31c (Griffith et al., 2004).

9. The following set of three photographs depicted the hardlands vegetation subtype of the Rio Grande Plains general mixed brush type. In describing this range vegetation Scifres (1980, p. 34) specified that the shallow soils of this subtype had calcareous deposits close to their surfaces. Dominant shrubs included blackbrush, guajillo, twisted acacia, and other Acacia spp. while other common woody species included granjeno or spiny hackberry, cenizo, lotebush, and knifeleaf condalia (Condalia spathulata). Woody shrubs present in lesser proportions included Berlandier wolfberry, javelina bush, agarito, Texas persimmon, cactuses, Yucca spp., and and lime prickly ash (Zanthoxylum fagara).

The extremely limited density, cover, and relative proportions of mesquite and huisache suggested that this range plant community was not just another example of an overgrazed, underburned, gone-to-brush, degraded range. While density and cover of woody plants had almost assuredly increased from pre-Columbian conditions (this was afterall Texas with its several centuries tradition of overuse and overgrazing of ranges), this "photo-quadrant" sample probably represented an example of more-or-less natural Rio Grande Plains savanna on a shallow caliche habitat.

The various references cited above for guajillo ridges and mixed brush uplands subtype also applied for the hardlands subtype with specific Gramineae species obviously varying by range site.

Hardlands Rio Grande chaparral- An extremely shallow, primarily clay soil that was overlaid by an interrupted calcareous layer (caliche) provided an edaphic environment conducive to development of a remarkably diverse range plant community. Guajillo and cenizo were the most abundant species, but there were not obvious dominants. Rather this example of the hardlands chaparral subtype of "mixed brush" was mostly an "equal parts" mixture of knifeleaf condalia, Berlandier woldberry, cilindrillo or tomatillo, javelina bush, granjeno, agarito, Spanish dagger, blackbrush, myrtle-croton or southwest bernardia (Bernardia myricifolia), and the cactus known variously as Texas or Englemann or Lindheimer pricklypear (Opuntia englemannia var. lindheimeri= O. lindheimeri) as well as guajillo and cenizo.

There was an herbaceous understorey made up almost exclusively of buffalograss. There was--not surprising-- a DYC (damn yellow composite), bristleleaf dogweed (Dyssodia tenuiloba= Thymophylla tenuiloba= Boebera tenuiloba).

Live Oak County, Texas. October, autumnal aspect. FRES No. 32 (Texas Savanna Shrubland Ecosystem). K-54 (Mesquite-Acacia Savanna). SRM 728 (Mesquite-Granjeno-Acacia). Mixed Deciduous Series of Tamaulipan Thornscrub biotic community (Brown et al., 1998). Southern Texas Plains- Texas-Tamaulipan Thornscrub Ecoregion 31c (Griffitth et al., 2004).

Rio Grande Plains mixed shrub-shortgrass savanna- Range vegetation portrayed here represented the deciduous shrub-mixed prairie savanna in something resembling what was interpreted by prominent ecologists (Kuchler, 1964, p. 61; Scifres, 1980, ps. 30-34) as natural or climax vegetation. Shrubs were almost certainly somewhat more plentiful than in the virgin vegetation, but this was about as good an approximation as can usually be found. The herbaceous understorey was a consociation of buffalograss. Past overgrazing may have greatly reduced less grazing-tolerant grasses like little bluestem, silver bluestem, sideoats grama, pink pappusgrass, and bristlegrasses leaving an herbaceous layer consisting exclusively of a shortgrass species. Buffalograss might likely have been the predominant --though not the only-- grass even in pristine condition on this shallow clay soil.

Physiogonomy, species composition, and range community structure appeared to approach what was described as virgin range vegetation. This example of the hardlands subtype of Rio Grande Plains savanna matched closely the description of Class 2 of the Texaas Savanna Ecosystem given by Garrison et al. (1977, p. 40). The range vegetation presented in this present photograph and in the close-up photograph immediately below matched closely the vegetation in the photograph used by Kuchler (1964, p. 61) as an example of the potential natural vegetation. The example shown by Kuchler (1964, p. 61) was of range vegetation that obviously was on deeper soil and-- as evidenced by presence of numerous very young mesquite saplings-- that had been recently invaded by the dominant, defining species.

Live Oak County, Texas. October, autumnal aspect. FRES No. 32 (Texas Savanna Shrubland Ecosystem). K-54 (Mesquite-Acacia Savanna). SRM 728 (Mesquite-Granjeno-Acacia). Mixed Deciduous Series of Tamaulipan Thornscrub subdivision (Brown et al., 1998). Southern Texas Plains- Texas-Tamaulipan Thornscrub Ecoregion 312c (Griffith et al., 2004).

Interior of hardlands subtype of Rio Grande Plains mixed shrub chaparral- Close-in view of Tamaulipian Thornscrub vegetation that developed on a caliche outcrop, shallow, clay soil in South Texas Plains vegetational area. Herbaceous layer was a consociation of buffalograss. It was likely that taller, less grazing-tolerant grasses like little bluestem, silver bluestem, sideoats grama, and plains bristlegrass had been reduced to near elimination by overgrazing, but there was no scientific proof of such range retrogression. Conspicuous shrubs were nopal or Texas or Lindheimer pricklypear and Spanish dagger. Other woody species included granjillo, Berlandier wolfberry, agarito, knifeleaf condalia, cenizo, granjeno or spiny hackberry, and javelina bush.

Live Oak County, Texas. October, autumnal aspect. FRES No., 32 (Texas Savanna Shrubland Ecosystem). K-54 (Mesquite-Acacia Savanna). SRM 728 (Mesquite-Granjeno-Acacia). Mixed Deciduous Series of Tamaulipan Thornscrub biotic community (Brown et al., 1998). Southern Texas Plains- Texas-Tamaulipan Thornscrub Ecoregion 31c (Griffith et al., 2004).

10. Guajillo or Berlandier acacia (Acacia berlandieri) on Rio Grande Plains- Specimen of guajillo at fruit-ripe/seed-shatter stage growing on a stoney, sandy ridge in the guajillo ridge-mixed shrub subtype of Rio Grande Plains Chaparral (the example vegetation that was shown above). Guajillo and cenizo were the dominant range species on this example of Tamaulipian Thornscrub Savanna.

Live Oak County, Texas. October.

11. Torrey croton (Croton torreyanus= C. incanus)- This specimen of Torrey croton was grwong on the example of guajillo ridge-mixed shrub subtype of South Texas Chaparral presented above in four photographs. Gould (1962, p. 56) listed 19 Croton species (several of which consisted of different varieties) growing in Texas. These included shrubs and forbs with both annual and perennial forb species. Torrey croton is a shrub, but its stems (shoots) are typically suffretescent or suffruticose such that upper parts of shoots frequently die back sometime each year (ie. upper portions of stems are annual organs). That condition was clearly visible in this photograph (it appeared that there were more dead than live annual shoots).

Live Oak County, Texas. October.

13. Sward of understorey of guajillo ridge-mixed surub subtype- Detail of herbaceous layer of the general mixed bursh type of Tamaulipan Thornscrub (Rio Grande Plains "brush country") of the example shown above. Dominant grasses were silver bluestem and shortspike windmillgrass. Other grass species that were present in smaller propotions included little bluestem, sideoats grama, buffalograss, curly mesquite, plains bristlegrass, and reverchon bristlegrass.

Common bermudagrass (Cynodon dactylon) was also commonly present, but this species was limited to perimeters of ranges adjoining highway rights-of-way and it was not known if bermudagrass had naturalized or existed locally only as an adventive species. At some locations (but not the one from which these examples were taken) King Ranch bluestem (Andropogon ischaemum= Bothriochloa ischaemum) and buffelgrass (Pennisetum ciliare) were naturalized species in the sward of Tamaulipan Thornscrub range vegetation.

Live Oak County, Texas. October.

14. Plant of shortspike windmillgrass (Chloris subdolichostachya)- Shortspike windmillgrass is often a dominant grass on Rio Grande Plains shrub-grass savanna. Gould (1975, p. 327) concluded that this species was a natural hybrid derived from crosses between hooded windmillgrass (C. cucullata) and common windmillgrass (C. verticillata) and crosses between hooded windmillgrass and slimspike windmillgrass (C. andropogonoides).

Shortspike windmillgrass is one of the most strongly stoloniferous of Chloris species, many of which are strictly tufted (= cespitose) species (ie. all lateral shoots are tillers). Due in large part to its stoloniferous habit C. subdolichostachya is frequently a dominant grass species, especially at local scale, in the South Texas "brush country". A similar situation exists with regard to buffalograss (recall photographs presented above of the hardlands subtype of the deciduous mixed shrub savanna) and curly mesquite on South Texas Plains Savanna.

Shortspike windmillgrass is commonly a species of disturbed conditions (eg. situations of overgrazing or overmowing). No doubt this is largely due to the stoloniferous habit of this species. (Other stoloniferous grass species like buffalograss and curly mesquite are also frequent dominants of the Tamaulipan Thornscrub.

Live Oak County, Texas. October.

15. Inflorescences of shortspike windmillgrass- Two views of flower clusters of C. subdolichostachya. Interpretation and description of the inflorescences of Chloris species remains a confused affair. Traditionally the Chloris inflorescence was viewed either as 1) a group of spikelike racemes, a raceme being the Gramineae inflorescence type in which spikelets are pedicellate-- on a pedicel or short stalk-- on the rachis or central stalk of infloresecnce, or 2) an arrangement of one-sided spikes with or having sessile spikelets (Hitchcock and Chase, 1950, ps. 22, 519; Chase, 1964, ps. 54-57) consistent with the historic Chlorideae tribe .Gould and Shaw (1983, p. 120) described the Chlorideae inflorescence as "a unilaeral spike or of few to several unilateral spicate primary branches" while Gould (1975, p. 316) had previously characterized the Chloris inflorescence as ranging from "open to contracted panicles of few to several digitately to subdigitately arranged one-sided spicate branches".

Anyway, here is what the inflorescence looks like from both lateral and dorsal views. The inflorescence of C. subdolichostachya typically has only one whorl of "spicate branches" like C. cucullata rather than several such whorls as in C. verticillata.

Live Oak County, Texas. October.

18. Netleaf hackberry or palo blanco (Celtis reticulata= C. laevigata var. reticulata= C. dorglasii)- Interpretation of the specific standing of netleaf hackberry is varied and, thus, not precisely known. Some workers interpreted it as a distinct species while others viewed it as but one of several varieties of C. laevigata. Plants interpreted as reticulata (regardless of taxonomic level) grow from northern Mexico to the Interior Northwest of Washington and Idaho. In Texas netleaf hackberry occurs in all vegetational areas except the Pineywoods, Blackland Prairie, and Post Oak Savanna. It is often a locally dominant woody plant in the brush country of the Rio Grande Plains where its abundance beyond trace levels (other than locally, on specific range sites, or at microsite scale) is indicative of range degradation due to post-Columbian disturbances ranging from commercial developments like oil fields to a long human history of underburning, overgrazing, tillage, etc.

The small tree presented here was growing in the Coastal Prairies and Marshes land resource area adjacent to the Rio Grande Plains (Nueces County, Texas). October.

19. Leader of netleaf hackberry- Terminal part of major branch of netleaf hackberry. Nueces County, Texas. October.

20. Blackbrush or chaparro prieto (Acacia rigidula)- A young blackbrush was in full bloom in late winter. Looked like a high yield of seed-bearing legumes (wait 'til you see heavy harvest three slides later), but nothing is certain botanically (except more brush) in the uncertain weather of south Texas. This showy specimen was growing on the Gulf coastal prairie that neighbored to the east of the Rio Grande Plains.

Santa Gertrudis Division, King Ranch, Jim Wells County, Texas. February.

21. Inflorescences of blackbrush- Details of flower clusters on leaders (branches) of blackbrush. Acacia species are in the mimosa subfamily (Mimosoideae) of the Leguminosae (= Fabaceae). Some authors have placed members of this subfamily (including other major shrub genera like Mimosa and Prosopis of the Rio Grande Plains) in a separate mimosa family (Mimosaceae) and restricting Leguminosae to those taxa that bear the characteristic papilionaceous corolla of banner or standard, keels, and wings.

This latter interpretation has generally been rejected because, as presented below, all these species bear the classic "bean" fruit (= legume).

Santa Gertrudis Division, King Ranch, Jim Wells, County, Texas. February.

25. Ebano, ape's earring (and where did they come up with that one?), or Texas ebony (Pithcellobium flexicaule= Ebenopsis flexicaulis= Siderocarpus flexicaulis)- This native legume is also in the Mimosoideae subfamily of the Leguminosae. Texas ebony is a small tree or shrub, often the major source of shade where the same is a valued "commodity" (especially when combined with a breeze). Alone in shrub form or as a small tree growing in association with other woody species, ebano often forms dense thickets (as if there is a legume in the "brush country" that does form thickets).

The dense, dark heartwood of ebano is used for decorative items (eg. belt buckles).

San Patricio County, Texas. June.

Specifically, much of the nitrogen in the legumes is nonprotein nitrogen rather than amino nitrogen so that to accurately determine legume nitrogen contents Kjeldahl values should have been multiplied by 3 and not 6.25. In other words the crude protein values estimated and reported for legumes are twice as high as they really are. (T.D.A. Forbes, Texas Agricultural Experiment Station, Uvalde, Texas, personal communication).

For example, Subcommittee on Feed Composition and Committee on Feed composition (1971) listed the protein (N X 6.25) content of fresh common mesquite pods at 14.4% whereas this feedstuff was actually closer to 6.9%
( 3.0 = 48% then 6.25 0.48 X 14.4% = 6.9%).

Furthermore, members of the Mimosoideae have several secondary plant compounds (eg. tannins) which are detrimental, perhaps at subclinical levels, to ruminants, even to goats and deer. In final analysis, overgrazed ranges in the Rio Grande Plains are "sub-optimal" even for browsers like goats. This country was overstocked with livestock for several centuries and if the leguminous shrubs were palatable to domestic animals those shrubs would not be there now. They would have been grazed out as happened with the grasses. Instead, Acacia and Prosopis species are there because they were eaten less than the grasses and when fires were stopped fire cessation selectively benefited these woody legumes more than it did the grasses.

Most of these native woody shrubs have increased in cover, density, etc. due to mismanagement and retrogression of the rangeland is the result. At the levels at which these species now occur they are noxious range plants. Nor are high levels of such shrubs as are found on many south Texas plains ranges beneficial as habitat for white-tail deer or bob-white quail. Rangemen should do everything economically feasible and biologically possible to destroy these ecological woody invaders. After establishment of proper stocking rates, brush control is the first step in restoration of these once productive savannas.

30. Fruit-bearing leaders of huisache- Legumes and compound leaves on branches of huisache. Huisache is often called "sweet acacia" after it's use in the perfume industry. At the densities and crown cover at which huisache often grows on deteriorated ranges in the Tamaulipas savanna rangemen think of it as anything but "sweet".

Pima County, Arizona. June.

31. Mature huisache fruits- Ripened legmues of huisache showing some insect predation. Herbivory of range plants takes many forms. Students should never entertain the erroneous assumption that vertebrates like livestock and wildlife are the only range herbivores. Unfortunately, insects have not eaten enough huisache seeds to curtain the excessive invasion of this native plant at unnatural rates since man "progressed" from Noelithic burner of the range to a more technologically advanced range manager.

Pima County, Arizona. June.

35. A young mesquite sapling only 3 ½ feet tall producing a healthy crop of new mesquites amid western ragweed on “go-back land”-  “Girls by the mill pond about half-growed; jump on a man like a dog on a bone.” (Bob Wills and The Texas Playboys)                                                                     

Early sexual maturity is one adaptation (natural selection to insure survival of the most fit genes) of shrubs to harsh environments that include frequent burning and other forms of defoliation. This mesquite was approximately five years old. “Mesquite is usually fully mature after 3 years” (Scifres et al, 1973, p. 15).

38. Texas pricklypear and, though often causing confusion (and perhaps erroneous to boot) Englemann or Lindheimer pricklypear (Opuntia engelmannia var. lindheimeri= O. lindheimeri)- Shown here and in details of the next three slides is one of the most widely distributed cactus species. It's range extends from the Gulf Coast to the Pacific and from southern Mexico to central Oklahoma. The specific epithet lindeimeri has been proven conclusively to be in error, but it is still commonly used. To add further confusion (to be expected with any species as wide-ranging as this one) some authorities have included varieties of other species (eg. O. phaeacantha var. discarta) in their interpretation of O. engelmannia.

Powell and Weedin (2004, ps. 172-181) may have cut the Gordonian knot and resolved the matter once and for all (but don't bet the ranch on it) by distinguishing Texas pricklypear (O. englemannii var. lindheimeri) from Englemann pricklypear (O. englemannii var. englemannii) synonyms of which include O. englemannii var. discata, O. phaecantha var. discata, O. discata, and O. englemannii).

Whichever author(s) one follows this taxon remains one of the farthest-ranging cacti in North America. It is extremely common in the Rio Grande Plains and Trans Pecos Texas and throughout much of Mexico.

The neighbor to this specimen was the shrubby composite commonly known as mariola. Mariola was shown in full-bloom in several slides below under which it was discussed in greater detail.

Elephant Mountain Wildlife Management Area, Brewster County, Texas. July.

39. Texas prickly pear (O. englemannii var. lindheimeri= O. lindheimeri)- According to some authorities this species was incorrectly named and described as Lindheimer prickly pear (O. lindheimeri) based on a mistaken description that was actually a combination of two species, pads of one and fruit of another (Weniger, 1984, p. 245). The probability of such an error was increased by the wide distribution-- and thus much ecotypic variation and phenotypic plasticity-- of this "often misunderstood" species (Weniger, 1984, p. 245). Hopefully Powell and Weedin (2004, ps. 177-181) straightened out the confusion.

The large individual shown here (about five feet tall) had produced a number of large but still immature fruits (along the top ridge of the pads). The "pads" (a common layman's term) are actually the broad, circular-shaped stems (shoot segments) that have two different forms of appendages or sharp outgrowths (ie. "stickers" to employ another lay term) and small, ephemeral leaves (see below). The more technically precise term for these highly modified shoots or stems is variously (depending on reference) that of cladophyll, phylloclade, phyllode, or cladode (a modified, often flattened, photosynthetic stem or branch). Different botanists use these terms in slightly different detailed meanings. (It would appear that almost everything of a scientific nature about these amazing plants is interpreted in various ways by various taxonomists.) By whatever name they are known these highly modified shoots or branches bear either no leaves or short-lived ones such that photosynthesis (the water-conserving Crassulacean-acid metabolism, CAM, pathway) takes place in the stem. This stem is a trunk or bole in some of the larger cacti. This feature is an obvious evolutionary adaptation to water shortage. One of the most spectacular examples of convergent evolution is development of this leafless and succulent stem feature or trait in the spurge family (Euphorbiaceae) and the milkweed family (Asclepiadaceae) as well as in Cactaceae. This is standard textbook fare (see for eg. Raven et al. 1992, p. 518).

The mature fruit of prickly pear is a many-seeded berry often known as a "tuna" (Spanish). These tunas are the source of some of the finest jellies imaginable. They are also used for making candy. The "pads" have sometimes been used for human food as well, first learned by American Indians of course and later passed on to Mexicans and gringos.

The main concern with this species of prickly pear is as a brush (= a noxious plant) species resulting from all of the standard causes ranging from overgrazing, underburning, oil and gas development to climatic shifts. Englemann (and numerous of the other Opuntia species) are major feed plants for wildlife. They provide both browse as in case of the javelina or collared peccary (Tayassu tajacu) and mast (the fruits) for birds, coyotes, coons, etc. as well as for javelina. Under emergency feeding conditions, especially drought, Lindheimer or Englemann prickly pear is one of the major species of "pear" from which the spines are scourced for use as a major survival feed source for cattle and sheep. "Burning pear" (by use of propane burners) has been a principal duty of otherwise proud vaqueros or cowhands during drought that is so recurrent in the Southwest. O. englemannia is a "mixed blessing" on southwestern and southcentral ranges.

The Englemann prickly pear in this photograph was growing on a Sandy Loam range site dominated by blackbrush (Acacia rigidula) in the Rio Grande Plains. Chaparrosa Ranch, Zavala County, Texas. May.

40. Large Texas pricklypear in fruit- This old "pear" plant was bearing fruit, but the most obvious mode of reproduction in this clonal plant had been by vegetative (= asexual) reproduction: simply growing more cladophylls. The versality of both asexual and sexual reproduction was illustrated. A county road cut provided a favorable microsite for this representative of it's species.

Texas West Cross Timbers. Erath County, Texas. Late August.

Also visible in both of these slides are the epidermal appendages that are modified protective organs. These sharp outgrowths of the members of Cactaceae are of two major forms: 1) spines which are the long, sharp, usually woody, thorn-like "jaspers" and 2) glochids or spicules which are much smaller, hair- or bristle-like "stickers" usually having many tiny (almost microscopic) barbs. These appendages are usually interpreted as modified leaves or leaves reduced to spines as an obvious adaptation to reduce transpiration and increase survival in arid environments as well as adaptative defensive organs to protect these water-storing xerophytes from herbivores. Some cactus specialists and ecophysiologists interpreted spines, especially those resembling hairs (often even white in color), as adaptative structures to shade and insulate the fleshy shoots in order to prevent heat and/or wind injury as well as to reduce water loss by transpiration. Conversely, the insulation feature of these structures prevents heat loss and cold injury at night and in winter. Fluted trunks of cactus serve these same functions (Vankat, 1979, ps. 195-198).

One of the key characteristics of the Cactaceae is the presence of areoles, the area or location on the "pad" around which the spines and glochids (and ephemeral leaves) arise. Areoles are either raised areas (like a pimple) or depressions (ie. pits) which are openings in the epidermis. The areole is unique to the Cactaceae. Areoles are interpreted as buds because they are the source of leaves and the protective outgrowths of spine and glochid. Incidentially it is numbers of the latter organ which cause the most aggravation and irritation to animals (including man) which carelessly stray too close to these succulent species.The spines can obviously cause more injury, but the pesky glochids typically break off in the animal epidermis and are extremely difficult to remove due to the many tiny barbs arranged along the individual glochid.

Areoles, complete with conspicuous glochids and spines, were clearly visible on the pad shown in the second slide. Newly emerging ephemeral leaves were also visible around areoles below the apex of this shoot. Also clearly visible in this second photograph was a developing cactus flower in the center of the "ridge line" (apex) of the cladophyll.

Erath County, Texas. April.

43. Fruit of Texas pricklypear- The "ridgeline" of cladophylls (= cladodes) is location on which pear fruit is borne. The concave (dished) upper surface (dorsal or "top") of fruit is the umbilicus. It is the site where inflorescence had been attached. The fruit of the cactus family is a many seeded berry. A berry is a multiseeded, indehiscent, fleshy fruit in which the pericarp (fruit wall) is fleshy throughout; other examples of berries are grape and tomato. The cactus berry of many species, including Englemann pricklypear, is used for making of jellies and candy.

Texas West Cross Timbers. Erath County, Texas. Late August.

44. Flower of Texas prickly pear- An example of the beautiful inflorescence so characteristic of the Cactaceae. The circular arangement of numerous stamen is an obvious and attractive feature of the cactus flower. Unfortunately (from a human perspective) the blooms of most of the cactus species are notably short-lived, often persisting for only a few hours. Some of the most beautiful cactus inflorescences open solely at night when they are pollinated by nocturnal animals including insects, reptiles, birds, and mammals like bats. Even those that bloom at mid-day are opportunistic and infrequent as to their schedule, erratic precipitation events often dictating when sexual reproduction occurs. The more common and widely adapted species like many of those of Opuntia are less extreme in this regard. This example of O. englemannia var. lindheimeri was right "on schedule" by blooming in May in northcentral Texas (Erath County).

As is true for many perennial range plants, much (probably most) reproduction in Cactaceae is asexual by means of profuse production of cladophylls and their feature of rapid rooting upon physical separation of these fleshy shoots from the parent plant. Cactaceae members are yet other examples of clonal organisms in which individual segments of their fleshy stems ("pads") are modules or ramets of the genetic individual, the genet. A striking example of this was shown two slides below for the next species.

Technical Note: The partially out-dated reference, Brush Management - Principles and Practices for Texas and the Southwest (Scifres, 1980), is still the definitive bound source for descriptions, ecology, and key biological aspects of the major brush species in Texas and adjoining parts of neighboring states. Many of the specific brush control practices given by Scifres (1980) are obsolete (eg. 2,4,5-T, arguably the most economically effective broad-spectrum herbicide ever, has been off the market for nearly two decdes). For the current best brush control practices one should consult the various Cooperative Agricultural Extension Services, Natural Resources (= previously, Soil) Conservation Service, and/or field representatives of the various companies offering products and services for brush and weed control.

Naturalized variant of FRES No. 32, K-32 (Texas Savanna Ecosystem), SRM 728 (Mesquite-Granjeno-Acacia). Variant of Mesquite Disclimax Series of Brown et al. (1998). Southern Texas Plains-Texas-Tamaulipan Thornscrub Ecoregion, 31c (Griffith et al., 2004).

Naturalized variant of FRES No. 32, K-32 (Texas Savanna Ecosystem), SRM 728 (Mesquite-Granjeno-Acacia). Variant of Mesquite Disclimax Series of Brown et al. (1998). Southern Texas Plains, Texas-Tamaulipan Thornscrub Ecoregion, 31c (Griffith et al., 2004).

50. Curly mesquite (Hilaria belangeri)- Sward of curly mesquite. This is one of seven Hilaria species in North America, four of which are important range grasses. According to Gould (1951, p. 159) H. belangeri is the most palatable of these species, all of which are sod-forming (rhizomatous and/or stoloniferous). Curly mesquite has been the Hilaria species typically regarded by rangemen as a dominant of the "shortgrass country" (both shortgrass plains and overgrazed mixed prairie) and a species associated with such other shortgrass species as buffalograss and blue grama. Other vegetation specialists, particularly vegetation classifiers and mappers, in more recent works interpreted galleta (H. jamesii) as the dominant Hilaria on the Great Plains grasslands. For example, the Kuchler (1964, 1966) unit K-58 (Gramagrass-Buffalograss) did not list curly mesquite (Kuchler, 1964, p. 65). The Society for Range Management (Shiflet, 1994) did not even mention curly mesquite in descriptions of rangeland cover types SRM 705 (Blue Grama-Galleta) and SRM 715 (Grama-Buffalograss) of the Southern Great Plains Region. Dick-Peddie (1993, p. 104) gave galleta and not curly mesquite as the associate of the codominants, blue grama and buffalograss, of plains-mesa grassland. Curly mesquite does not grow in the central and northern Great Plains, but galleta occurs as far north as Wyoming so it is the Hilaria species sometimes found in rangeland cover type SRM 611 (Blue Grama-Buffalograss) of the Northern Great Plains Region.

In the experience of the current author omission of curly mesquite was somewhat erroneous, misleading to say the least. From his observations this author felt that Thomas (in Correll and Johnston, 1979, p. 11) was much "closer to the mark" when he listed curly mesquite immediately following buffalograss as a major increaser species on the Texas Rolling Red Plains portion of the Great Plains. Perhaps this was the reason why other (and more recent) authors did not list curly mesquite: it is an increaser and not a decreaser on most range sites (ie. it is not a climax species or a major species of the potential natural vegetation).

[By the way, this was still more evidence that SRM rangeland cover types typically resemble quite closely the climax or potential natural vegetation in spite of statements that explained SRM cover type "classification is based on existing vegetation" such that of these types "...most do not..." coincide with those of Kuchler (Shiflet, 1994, p. xi-xii). In fact the SRM rangeland cover types of the Great Plains province included essentiallly all of the Kuchler units of potential natural vegetation, and most of the other Great Plains rangeland cover types that did not correspond exactly with Kuchler units were smaller spatial subunits of these. One thing was certain: if qualifying statements given in Shiflet (1994, ps. xi-xii) were taken literally there would definitely have been far more reference to curly mesquite as well as a curly mesquite rangeland cover type. There are thousands of acres in the Texas Great Plains on which the dominant herbaceous species is curly mesquite, typically with honey mesquite as a scattered overstorey. This plains vegetation is a widespread form of depleted range: a seral stage on rangeland damaged by various combinations of former cultivation or "go-back land", severe overgrazing, oil and gas activity, and perhaps unique meteorological sequences of events or even climatic changes.]

The indespensible Pasture and Range Plants (Phillips Petroleum, 1963, p. 43) explained that curly mesquite had "increased and invaded ranges where better grasses were killed out by abusive grazing". Furthermore, curly mesquite is less palatable than buffalograss and blue grama and goes dormant earlier in drought all of which enable curly mesquite to survive "when better grasses die or thin out". While curly mesquite forms a dense sward such as the one shown here it's "forage production is very low when compared to the better grasses it replaced." (Phillips Petroleum Company, 1963, p. 43).

Regardless of successional status, forage value, soil cover, or usefulness as an indicator species, curly mesquite is-- for better or worse-- a nonclimax dominant on many ranges throughout much of southern Great Plains, a vast range region. In something of an overstatement when applied to the Rolling and High Plains Hitchcock and Chase (1950, p. 485) got the essence of the situation in regards curly mesquite: "Curly mesquite is the dominant 'short grass' of the Texas plains". (When the Rio Grande Plains are included this statement was "right on target".) Silveus (1933, p. 361) wrote that curly mesquite "is one of the most important grazing grasses on the Great Plains of Texas and New Mexico, extending into Mexico". Curly mesquite is commonly about the only perennial grass providing forage and soil protection over a large portion of Great Plains grasslands.

The examples in this section were from the Texas West Cross Timbers (Shally Hills range site) which is about the eastern limit of this species that is more typical of the semiarid zone. Erath County, Texas. Estival aspect in moderate drought,Late August.

53. Crawling across the rocks- Asexual (= vegetative) reproduction and the clonal structure of curly mesquite was obvious in this specimen as it sent out stolons and daughter plants over this sandstone. Note also however sexual reproduction by production of grain: "seed stalk" (culm with the fascicle arrangement of spikelets) in right foreground.

Erath County, Texas. Estival aspect in moderate drought, late August.

54. Curly mesquite runner- This stolon of curly mesquite had four daughter plants developing at nodes of the shoot. Curly mesquite is a clonal organism in which the genetic individual (the plant of an individual genotype) is the genet (= ortet) and the new daughter or sister plants are ramets (= modules) of the genet. Essentially all perennial plants are clonal organisms, but the new clones (modules or rametas) are very obvious-- hence the concept of clonal organization readily understood-- in sod-forming shortgrass species like curly mesquite and buffalograss.

Stolons are extravaginal shoots. They are secondary shoots arising out of the parent shoot (itself a secondary shoot-- as distinguished from the primary shoot that originated from the embryo asexual generations previously). In extravaginal shoots (which also include rhizomes) the new secondary shoots pierce or come up through the sheath, an organ of invaginated tissue (hence these piercing shoots are extravaginated). Intravaginated shoots are those which grow upward inside of (rather than piercing) the sheath. Intravaginal shoots are labeled tillers. Grasses whose secondary shoots are intravaginated (ie. tillers) have a tufted or cespitose growth form and are called "bunchgrasses". This is in contrast to "sod-forming grasses" like curly mesquite. (Some grasses like Indiangrass and many of the bluestems have both tillers and extravaginal shoots, especially rhizomes.)

Stolons and rhizomes are more effective than tillers in invasion of new ground by the genet (genetic mother plant). Said another way, extravaginal shoots are more efficient propagules for populating a plant's "resource frontier".

Erath County, Texas (Western Cross Timbers), Texas. Late August.

56. Curly mesquite spikes- Various portions of curly mesquite inflorescences were displayed for today's lecture. The infloresecence of curly mesquite (all Hilaria species for that matter) is a spike, an unbranched flower cluster-- the inflorescence-- in which the spikelets are sessile--without a pedicel or not pedicellate-- on the rachis. The rachis of curly mesquite is one of the most distinctive of any species of North American grass. It forms a right angle zig-zag pattern known to rangemen as the "crankshaft rachis".

Hilaria spikelets are arranged in fascicles, clusters or bunches, each of which (and each spikelet within which) is sessile. There are characteristically three spikelets per fascicle (two lateral spikelets, both of which have several florets that are each staminate, and a single central spikelet which is one-flowered and perfect).

Inflorescences in the second photograph were in various stages of maturity, including one that was immature (green).

Erath County, Texas. Late August, and after recent rains.

57. Pink pappusgrass (Pappophorum bicolor)- A shoot of one of the most distinctive and defining grasses of the Rio Grande and Tamaulipas Plains region, the infamous brush country. Pink pappusgrass is not one of the most palatable native grasses of this range type, the various range sites of which have as their natural potential (= climax), major Gramineae species as diverse as sideoats grama, buffalograss, curly mesquite, tanglehead (Heteropogon contortus), crinkleawn (Trachypogon secundus), longspike silver bluestem (Andropogon saccharoides var. longipaniculatus= Bothriochloa saccharoides var. longipaniculata), and Arizona or California cottontop (Triachne californica) . The intermediate (= fair) palatability of pappusgrass may be a major factor why it is locally abundant and generally fairly common on less depleted ranges in the Tamaulipas brushlands that were (many continue to be ) subjected to overgrazing and fire cessation for several centuries beginning with development of livestock ranching by the Catholic Church out of Spain.

Pink pappusgrass is a cespitose (= tufted) mid-grass-- a grass species of medium height relative to tallgrass and shortgrass species-- that attains a stature of two to three feet on more favorable habitats (sandy to gravelly soils). It's size and habit mirrors the general physiogonomy of the herbaceous understorey of the climax shrub-grass savanna. The biological range of pink pappusgrass extends from the Coastal Prairies and Marshes on the east, northward through the Edwards Plateau into the Rolling Red Plains and westward into the Basin and Range Province.

Bexar County, Texas. April.

59. Spikelets of pink pappusgrass- This portion of a panicle of Pappophorum bicolor presented the spikelets of this range grass. Pappophorum species are members of the small tribe Pappophoreaepae in the Eragrostoideae, the Gramineae subfamily that tends to predominate in warm or hot, arid and semiarid climates. The spikelets of this genus consists of several (usually four to six) florets, the lower one to three being fertile. The lemmas subdivide into numerous awns of varying lengths, and as the spikelet is shed (with florets remaining together as a unit) these awns appear as a pappuslike crown (Hitchcock and Chase, 1951, p. 225).

Bexar County, Texas. April.

60. Spanish dagger, Torrey yucca, or palma pita (Yucca treculeana= Y. torreyi)- This is the major (most widespread) arborescent lily on the Rio Grande Plains. Most contemporary authorities place Yucca species in the Agavoideae (agave subfamily) of the lily family (Liliaceae), but other authors put the yuccas in the Agavaceae (agave family).

Spanish dagger is also commonly found in other vegetational areas especially the Trans Pecos Basin and Range and Coastal Prariies and Marshes. This specimen was proudly growing the Wild Horse Desert portion of the Kenedy loose sand prairie that is part of the western Guld Coast prairie vegetation. Kenedy County, Texas. February, full-bloom phenological stage.

61. Tasty treat- Inflorescence of Torrey yucca, Spanish dagger, or palma pita, the large treelike Yucca species most common on parts of the Rio Grande Plains, Coastal Prairies and Marshes, and eastern Trans Pecos Basin and Range vegetational or land resource areas of Texas. Supposedly the flower cluster is used as a starchy food in Mexico. Many species of insects, birds, and quadraped mammals are extremely fond of the sweet taste of these flowers. This inflorescence was growing on the plant presented in the preceding photograph.

Kenedy County, Texas. February, full-bloom stage of phenology.

62. Rain lily or, sometimes, Cooper's rain lily, giant rain lily, white rain lily; also eveningstar (Cooperia pedunculata= Zephyranthes drummondi)- This member of the amaryllis group can be interpeted as being in either the Amarylloidideae (subfamily) of the Liliaceae or the Amarylldcaceae (amaryllis family). Its biological range is rather restricted extending from northcentral Texas into northern Mexico. In Texas this species occurs in the Blackland Prairie, Cross Timbers and Prairies, Edwards Plateau, and Rio Grande Plains vegetational areas. In a restricted area of Texas this particular species causes primary photosensitization (Hart et al., 2003, p. 74). It was included here because it is one of the more conspicuous forbs in the Rio Grande Plains, especially on deeper sands.

Diggs et al. (1999, p. 1200) distinguished between C. drummondii the habitat of which is shallow, calcareous soils and C. pedunculata that grows on a greater diversity of habitats, including sandy soils. According to these authors the former species blooms in late afternoon or evening whereas the latter species blooms from late night to early morning. The "morning bloomers" shown here played by the rules. As was characteristic of their species these plants emerged and flowered "almost immediately" after a good, soaking rain that broke a summer-long drought. These specimens were growing on sandy land of the West Cross Timbers.

Erath County, Texas. Late August.

Atascosa County, Texas. Autumnal aspect, October. As was the case of the live oak-mixed prairie savannah this vegetation defies precise FRES and Kuchler designations, primarily perhaps because these classifications did not involve mapping  at this fine a scale. This community could be interpreted as a cover type variant or form  of K-72 (Oak Savanna) though in physiogonomy it clearly resenmbles the Florida live oak hammock which seemed to be most closely K-81 (Live Oak-Sea Oats). Yet, it is not the coastal live oak- sea oats understory. Neither is there an SRM designation. East Central Texas Plains- Southern Post Oak Savanna Ecoregion, 33b (Griffith et al., 2004).

67. A woodland on the coastal sand prairie- A live oak woodland had developed on the Kenedy sand prairie (Johnston, 1963, p. 460), one form or subtype of Gulf coastal tallgrass prairie inland from the coast but within the Texas Coastal Prairies and Marshes Area. Seen from perspective of Landscape Ecology this range vegetation (these units of hardwood evergreen woodland), ecosystems, and/or landscape elements could be interpreted as patches of live oak woodland in a matrix of seacoast bluestem (Andropogon littoralis= Schizachyrium scoparium var. littorale)- sacahuiste or Gulf cordgrass (Spartina spartae) coastal prairie. From the classical viewpoint of savanna as put forth by Dyksterhuis (1957) this overall grassland-woodland landscape could be seen as a savanna in which units or assemblies of woody vegetation ranging from smaller mottes (Texan for "groves") to extensive "woods" of several hundred acres are the physiogonomic equivalent of vegetation consisting of individual to "a few" trees and/or shrubs isolated on grassland. In other words, this would be a savannah in which the woody elements are larger and include more woody plants (eg. groves) rather than the typical situation of scattered individual trees and/or shrubs. This would not necessarily imply that such a structural or physiogonomic savannah was a successional or genetic (as to origin) savanna, this latter of which is the usual definition or, at least, connotation of an ecotone (a transition) from herbaceous to woody vegetation.

Interpretation of the woody vegetational units perhaps would hinge on whether mottes or woodlands were actually one up to "just a few" genetic plants whose individual stems (trunks or boles) were repeating clonal units or, alternatively, if these groves or woodlands were composed of many genetic individuals (each or most trees as denoted by a single tree trunks were derived from one embryo, that is, one acorn).

Range vegetation shown here was part of what has long been known as the Wild Horse Desert part of the Rio Grande Plains. This native grazing land is a slightly rolling or hummock aeolian plain of sand entitled the "Kenedy loose sand prairie" that consist of different range plant communities as "a tight mosaic of vegetation types..." (Johnston, 1963, p. 460). The uncertain successional status of large live oak mottes like the one shown here that develop on loose sand uplands was mentioned briefly in the caption of the immediately succeeding slide. The present photograph illustrated the spatial arrangement of sandy sachuiste prairie and mottes dominated by live oak that attest to the "very complex mosaic of vegetation types" (Johnston, 1963, p. 460) of the Wild Horse Desert on the Rio Grande Plains.

Norias Division, King Ranch, Kenedy County, Texas. February, late hibernal or early vernal aspect.

68. Live oak motte turned woodland- Exterior view of a live oak woodland or forest (larger than typical live oak motte) situated within seacoast-sacahuista tallgrass coastal prairie. The dominant herbaceous plant growing at perimeter of live oak woodland was Gulf cordgrass or sacahuista. Other tree species present--at rare to trace amounts of canopy cover--werehoney mesquite (Prosopis glandulosa) and common hackberry or sugarberry (Celtis laevigata). Even though crowns of trees produced a fairly closed canopy with considerable interlocking of branches there was a well-developed (e) herbaceous understorey (often consisting of two to three layers) as well as a second (lower) woody layer or understorey of shrubs and small (immature) trees.

Areal extent (acreage) of this live oak-dominated range community was considerably larger than typical live oak mottes and therefore was viewed more as a live oak woodland or forest rather than as a grove of trees within or on a prairie. Perhaps this distinction was arbitrary or even incorrect but, as in the case for fire behavior, at some point size (spatial scale) becomes an ecologically critical feature. Impacts and role of fire would be a case in point. Prairie fires could easily burn under or scorch crowns of small mottes whereas with expansive woodland areas there would places where fire could not reach (ie. as size of live oak-dominated stands increase in area there is in