Tallgrass Savanna
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1. Little bluestem-live oak savanna- This is the Texas live oak-tallgrass savanna at climax stage. As a single-species understory to old-growth live oaks, little bluestem forms a consociation almost to complete exclusion of any other herbaceous species. The only contender (and it is barely that) for an associate species is, interestingly, the annual colonizer of old-fields known variously as marestail, horse-weed, or old-field fleabane (Conyza canadensis= Erigerion canadensis). There is good regeneration of the live oak. (Note young trees at far left margin of slide and the clump of young trees with gray trunks immediately behind and to the right of the the right front mature live oak.) A bromeliad known as ball moss (Tillandsia recurvata) is growing on branches of the live oaks. This is as beautiful and pristine a savanna as the author ever encountered.

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).

The Cross Timbers is, or are (as the grammatical case may be), some of the more unique and enigmatic kinds (or forms, expressions, etc.) of vegetation in North America. Besides being used as a term for a “vegetation type” and an ecosystem or landscape of a geographic region-scale, Cross Timbers also entered into regional history, literature, and cultural-social character features. Washington Irving  probably did the most to essentially enshrine Cross Timber[s] in his famous A Tour on the Prairies (1835). Later, Cross Timbers became a long-established trademark-like catch word for commercial use in regional promotion of real estate, tourism, and so on. Cross Timbers took on poetic and historic connotations as well as general biological and specific ecological meanings and descriptions. By and large these different usages, views, or ways of seeing the Cross Timbers complemented each other and made for a term or term-like phrase equal in its own way with the likes of Great Plains, Piedmont, Edwards Plateau, pine barrens, Great Lakes forests, Flint Hills, Ozarks, Great Basin, Palouse Prairie, or Pacific Northwest.  In these instances of common common “every day”usage, at least with some groups of people, Cross Timbers as the specific name of a physiographic province or plant formation became merged in common parlance with the general name for a region which in turn might be a combination of strict geologic or cartographic interpretation with basic biological features and historic-economic-cultural characteristics. Such is the very definition of Geography, and Cross Timbers is a geographical as well as an ecological designation.

In this context, readers have been blessed with an outstanding treatise of the Cross Timbers in The Cast Iron Forest (Francaviglia, 2000). This comprehensive account along with Dyksterhuis (1948) and Bruner (1931), both of which were referred to below, will provide beginning students with all they need to know to understand the regional range community and the range cover type long recognized and designated the Cross Timbers. Another recent, and also outstanding, treatment of the Cross Timbers is that of Hoagland et al. in Anderson et al. (1999, ps. 231-245).

A thumbnail sketch of a few basic features of this range vegetation seemed in order. The Cross Timbers is generally a savanna as a transition zone between the westernmost outpost of the oak-hickory forest and the eastern edge of the great interior grasslands known as tallgrass prairie. The Cross Timbers is climax vegetation. This vegetation extends from Texas northward and slightly eastward to southern Kansas. Cross Timbers generally occurs on soils for which the parent material is sandstone of various geologic ages (Francaviglia, 2000, Fig. 1-8, p. 24). As tree-dominated or, at least, tree-containing communities in North America go, the Cross Timbers have probably been less altered by white man than most native vegetation of which trees are or were a major component. Lastly, but by no means completely, Cross Timbers remains a major range type from standpoints of both a subject in Plant Geography and Synecology and as natural resources having substantial economic and cultural importance. This is true in particular for the beef cattle industry.        

In Oklahoma, Cross Timbers occur on the Central Redbed Plains, the Eastern Sandstone Cuesta Plains (Francaviglia, 2000, p. 23), and northward through the Chautauqua Hills and Osage Questas physiographic provinces which extend through southeast Kansas on which Cross Timbers also developed and remain a climax range type. The older and more familiar names for the last three of these is Sandstone Hills and Chautauqua Hills or, more generally, Sandstone Hills (Fenneman, 1938, ps. 613-614, 616-617, Plate VI).

South of Oklahoma’s Red River the major physiographic provinces supporting Cross Timbers are the Redbeds Plains and Commanche Plateau (Fenneman, 1938, Plate VII), or bordering along the Edwards Escarpment and Lampassas Cut Plain of Texas (Fenneman, 1938, Fig. 27, p. 102). South of the Red River the Cross Timbers (ie. the Texas Eastern and Western Cross Timbers) are in the West Gulf Coastal Plain of the Coastal Plain Province (Fenneman, 1938, ps. 100-103). An instructive indication of the close relationship between physiographic province and general or regional plant community (sub-formations) was shown when Fenneman (1938) labeled on his plates and figures both the Eastern Cross Timbers and Western Cross Timbers.

The Cross Timbers is (are) one of several ecotones or transitions between the deciduous forest formation of eastern North America and the climax tallgrass (Andropogon-Sorgastrum) prairie to the west. The definitive authority of the eastern deciduous forest remains Lucy Braun who interpreted the Cross Timbers as part of the "forest-prairie transition" of the oak-hickory forest region (Braun, 1950, ps. 177-178). Earlier in the seminal study of Oklahoma vegetation (Bruner1931, ps. 108- 110, 115-116, 129, 142-148) treated the Cross Timbers as an "oak-hickory savanna". Dyksterhuis (1957, p. 437) applied savanna as a concept and term to the Cross Timbers. More recent descriptions and interpretations retained the savanna designation although Francaviglia (2000, p. 119) concluded that from more detailed accounts (especially one by W.L. Ormsby, Jr) Cross Timbers generally "referred both to a forest with a dense, nearly impenetrable understory as well as to a more open, savanna-type forest with fairly widely spaced oak trees".

6. Oklahoma Cross Timbers- This is a textbook view of Cross Timbers in the Osage Questa province in Excellent range condition class. This is a Shallow Savannah range site dominated by the Four Horsemen of the Prairies with tall dropseed, purpletop (Tridens flavus), beaked panicum, and sand lovegrass as associates. Blackjack and post oaks are the dominat trees with hickory and American and red elm scattered.

"As I sit here today many miles I am away,
from the place I rode my pony through the draw;
Where the oak and blackjack trees
kiss the playful prairie breeze,
in the Oklahoma hills where I was born."

---- Oklahoma Hills, Woody Guthrie

7. Detailed interior view of post oak-dominated and brush understory form of Cross Timbers (Oklahoma)- This is a three-layered (-storied) Cross Timbers community growing in the heart of the Sandstone Hills. The understorey consisted of two layers. The taller layer (hence middle storey between tree canopy and lower shrub storey) consisted of redbud and cedar elm as shrubs or lower-stature trees entangled with vines (lianas) of greenbriar and grape. The lowest storey was dominated by the short, colony forming shrub generally known as buckbrush (Symphoricarpos orbiculatus). Seedlings and saplings of post oak were components of both these layers, hence of all layers of this vegetation. The most common herbaceous species was the rather infrequent coneflower commonly called blackeyed susan (Rudbeckia hirta).

This local Cross Timbers community had been excluded from burning for a number of years. Consequently it developed this multi-storied architecture of woody plants instead of the natural, open understorey comprised primarily of herbaceous species.  The vegetation seen here should be compared to the local Cross Timbers community shown in the next three photographs. The latter had been subjected to some recent surface fire(s) and had the herbaceous understorey characteristic of the climax Cross Timbers savanna.  

8.  Interior view of Oklahoma Cross Timbers with open herbaceous understorey – This is an example of a well-developed (and well-managed) climax Cross Timbers community with post oak and blackjack oak co-dominant and black hickory (Carya texana) the associate tree species. Often one or the other of these two oak species is the dominat of a Cross Timbers stand with the other species being either the associate or, sometimes, infrequent to absent. This condition is manifested as either a post oak or blackjack oak form or subtype. Bruner (1931, ps. 143-146) explained that blackjack was better adapted to drier, sandier, and generally less favorable habitats than post oak. He reported that blackjack was generally an inferior competitor with more tolerant, mesic species but that a mixture of both of these oaks was “… characteristic where the association [oak-hickory savanna] is well developed” (Bruner, 1931, ps. 146-147). In this section of his monograph Bruner (1931, esp. p. 147) listed the third dominant as Hicoria buckleyi (black or Buckley’s hickory formerly named C. buckleyi and, earlier, as H. buckleyi and now identified as C. texana) which he found to be more common on more favorable local habitats especially those with soils of higher clay content and on north or east slopes (ie. more mesic micro-sites). 

All three of the dominants of the oak-hickory savanna association were well-represented (common and widely distributed) in the stand shown in this and the next two slides. These three photographs caught the Oklahoma Cross Timbers at ultimate development. These examples, complete with the  “clear” herbaceous understorey maintained by fire, showed this range cover type at its zenith.Vegetation seen in these three slides should be compared back to the immediately preceding slide which showed vegetation of unburnt Cross Timbers on similar habitat (the same range site).   Dominant herbaceous species was upland switchgrass, which was consistent with this more mesic site as indicated by abundance of black hickory. Canada wildrye appeared to be the second most common grass (and, in fact, was a local dominant on some micro-sites) while the associate herb was the forb, black- (= brown-) eyed susan, that appeared very conspicuous in this view.

The foremost tree was post oak while the other two large trees to the right of the post oak were blackjacks. 

9.  Interior view of Cross Timbers in Sandstone Hills of central Oklahoma- This is the second of three photographs that presented a detailed view inside of a well-developed community of Oklahoma Cross Timbers that approached species composition of the climax vegetation.. Dominant tree species were post and blackjack oaks with black hickory as the associate tree species. The tree in right foreground was a mature (though not ancient) black hickory. The bark, shape of bole, and leaves were representative of this species. Trees in background were primarily young post oaks. Conspicuous forb was black-eyed susan. Switchgrass, Canada wildrye, and beaked panicgrass were dominant grasses in roughly that order. An unidentified sedge (Carex) species was also present. Species present were primarily those of the climax vegetation, but their relative proportions were a departure from the composition of the climax savanna. “Guestimated” percentages (based on rough estimates of cover, density, etc.) of herbaceous species were reduced while those of the woody species were increased over that described for pre-Columbian vegetation (hypothetical reconstructions based on examples of relict vegetation, early journal accounts, succcessional studies, etc. used as the basis of range site descriptions). Relative small size and juvenile age of most trees (eg. those in background) suggested that there were recent increases in tree regeneration and canopy cover most likely due to fire suppression and related human-induced impacts such as periodic overgrazing or vehicular traffic. The presence of black hickory, the most mesic of major Cross Timbers tree species, indicated that this site on a north slope was favorable for growing a dense stand of trees in the unnatural absence of natural, recurrent fire. Note, however, that some fairly recent surface fire(s) had “cleaned up” (to a degree) the understory such that there was an herbaceous understorey rather than the “brush patch” or “tangle” architecture of unburnt Cross Timbers such as that shown two slides above this photograph. 

10.   Interior of Cross Timbers in Sandstone Hills of central Oklahoma- This is the last of three slides that showed a typical interior of well-developed Oklahoma Cross Timbers. Vegetation consisted of climax species but not with the climax proportions of those species there having been an increase in tree density and canopy cover with some human disturbances (primarily reduction in natural fire). The Cross Timbers community shown in this and the two slides immediately above had been subjected to some relatively recent fire(s) with the resultant open herbaceous understorey. This interior architecture should be compared to that of unburned Cross Timbers which allowed development of a dense woody understorey (complete with two or three layers of woody plants). An example of this “thicket-like” form of Cross Timbers that results from fire exclusion was presented in the third slide above this one. Even with recent “burning off of the woods” the Cross Timbers vegetation shown in this and the two preceding slides had been fired so infrequently relative to the estimated historic fire regime that the community was more a woodland than a savanna.

Trees in the foreground were blackjack oak (the left-most tree and the two right-most and closest foreground trees) and post oak (two remaining trees; the second on the left and the one behind and to the left of the right-front blackjack). Dominant (and conspicuous) grass was switchgrass with Canada wildrye and beaked panicgrass also prominent. Dominant forb was black-eyed susan.

11.  Scrub blackjack oak form of Cross Timbers- Blackjack oak dominates the Cross Timbers on the harsher (drier, shallower) sites. This was explained above under slides of Oklahoma Cross Timbers using descriptions cited from the classic, definitive works (eg. Bruner, 1931, Francaviglia, 2000). Shown here was a consociation of the scrub or shrub form of blackjack. This can be compared to the tree form of this species shown in the immediately preceding and immediately succeeding slides. The blackjacks shown in these slides grew on a north slope and hillcrest of a north slope, respectively, whereas the blackjacks shown here grew on a south slope. It was the same range site (Shallow Savanna) in all slides with the major difference being north- versus south-slope aspect. However, a most interesting phenomenon and comparison between these habitats was that upland switchgrass was the dominant understorey species on all three! The unmistakable leaves and panicles of switchgrass were prominent in the left foreground of the present slide. Switchgrass grew only at edges of and in interspersed openings among the larger thickets of blackjack. The hard, undecomposed leaves that had fallen from the blackjacks formed mats or mulches around bases of the shrubs that were from two to six inches in depth. Leaf litter combined with the shade from green leaves on the oaks effectively excluded all other plant species from the blackjack thickets. Such layering of blackjack leaves from several previous seasons was ready fuel for fire. Any such fire would scourch the blackjacks to the point of top-killing them resulting in more swithcgrass and smaller blackjacks (following regrowth) with less woody cover. The unnaturally high proportion of blackjack cover seen here is a disturbance climax brought about by man’s elimination or, at least, reduction of natural fire regimes.

12.   Blackjack oak-dominated Cross Timbers in Sandstone Hills of central Oklahoma- This is the blackjack oak form or phase of Cross Timbers savanna with unusually high recruitment of oak and consequent exclusion of herbaceous species. This single-species stand (consociation) of blackjack oak developed on a rocky hilltop on the crest of a north slope.  All age classes of blackjack were present with older oaks growing into the tree form rather than the shrub or scrub oak form shown in the   immediately preceding slide. The older blackjacks were not as large as those photographed growing on north slopes with post oaks and black hickory, but the local habitat viewed here was more favorable than the shallow soil and south slope that restricted development to the scrub thicket formshown in the preceding slide. Also, present on this northern aspect hillcrest was a second layer of woody plants that was made up largely of buckbrush. Switchgrass (the dominant grass), little bluestem, Canada wildrye, and broomsedge bluestem were present but extremely sparse in small open spaces scattered among trees. None of these spaces or patches were visible here. An unidentified species each of Carex and of moss (Musci sp.) dominated microsites formed by shade from trees. This was visible in foreground of the view shown here.

13.  Blackjack oak trees top-killed by intense prescribed fire on tallgrass prairie- This and the following slide were included to show readers the size of blackjack trees that can be top-killed by fire on tallgrass prairie and associated savannahs like the Cross Timbers. Blackjacks over 15 feet in height were top-killed by an intense heading fire set at base of this slope and fueled by the dry matter (necromass) of tallgrass species (big bluestem was dominant with Indiangrass and little bluestem associates) that accumulated from deferment in the previous growing season. The prescribed burn was conducted about six weeks prior to the time of this photograph. It was a hot fire and totally killed all blackjack tissue above ground level.

This was big bluestem-dominated tallgrass prairie (the big bluestem phase or form of tallgrass prairie, bluestem prairie, which is more mesic than the Indiangrass and little bluestem-dominated forms). This form usually is more productive of biomass (higher-yielding) and produces more (perhaps not a lot more) fuel than the less moisture-requiring and generally lower-yielding latter two species. This bluestem prairie on the Osage Questas physiographic sub-province is part of a tallgrass prairie and oak-hickory-tallgrass savanna complex (a mosaic of these general, major communities) that also includes the Flint Hills to the west and the Chautauqua Hills “inserted” inside the Osage Questas. It is the sandstone-derived Chautauqua Hills that precisely speaking are part of the Cross Timbers, but blackjack and post oaks do not rigorously conform to such precise divisions as these which geologists and ecologists delight in delineating. Thus it was that blackjacks had “lite out from where they belong” in the adjoining Cross Timbers and invaded the pristine virgin sod of the bluestem and Indiangrass prairie pastures. Contemporary prairiemen took a lesson from the orally trasmitted knowledge of numerous Indian tribes that had at one time or the other claimed this former magnificent buffalo-elk range and fired the prairie to once more rid it of the woody scurge that would deplete it’s forage resource. Cowboy meaning: a roaring up-slope fire “did in” the blasted damn blackjacks and let the grass get the upper hand.

This and the next slide showed beginning— and perhaps not so beginning —students of Range Management how effective prescribed burning can be in maintaining grasslands and savannahs against excessive woody encroachments. Even though these two photographs were of neighboring tallgrass prairie vegetation and are not technically speaking that of Cross Timbers, they illustrated perfectly how fire maintains the “balance” (proper proportions) between woody and herbaceous climax species in the potential natural vegetation of savannas like the Cross Timbers that are neighbors to some of God’s greatest fire-maintained grasslands.

14.  Blackjack oak trees top-killed on bluestem prairie by prescribed burning- A hot heading fire about six weeks prior to this photograph was used to completely top-kill blackjack oaks that invaded virgin big bluestem-dominated prairie from neighboring Cross Timbers. The bluestem pasture was fired when the blackjacks and grasses were dormant. The typical stimulus-like response of big bluestem and Indiangrass to spring burning was evident in this post-burn view, but the blackjacks also responded with immediate resprounting from stumps and roots. Yes it would take more than one intense “hotter ‘n hell” fire to rid this luxuriant range of the invading blackjack oak, but one fire effectively killed or eliminated what was surely two decades or more of oak growth. Prescribed fire but once in four or five years will control blackjack oak to its proportion of species composition in the climax grassland (ie. reduce oak crown cover to levels approximating those of the potential natural vegetation), and make more grass forage for buffalo, elk, beef cattle, etc.and more meat for top-order carnivores such as man.

Note height of sprouts of both blackjack oak and smooth sumac (the latter along extreme right margin of slide). Observe also the absence of grass under blackjacks in pronounced circular patterns. This latter phenomenon can be extrapolated back to the pattern observed above for the blackjack shrub thickets on south slopes in the Sandstone Hills Cross Timbers (three slides immediately above this slide).

15. The Texas West Cross Timbers- This is the brush or thicket form of the Cross Timbers. It is the kind that Washington Irving must have had to pass through when he described the Cross Timbers as “forest of cast iron”.  It is the “vegetal type” named and described by Dyksterhuis (1948) as the “Quercus-Smilax type” on sandy Red and Yellow Podzolic soils of gentle to moderate slope. Dyksterhuis (1948, p. 341) found the mostcommon grass to be fringeleaf paspalum (Paspalum ciliatifolium). In this parcel sand dropseed (Sporobolus cryptandrus) was the clear dominant grass, but silver and little bluestem, sideoats and hairy grama, common grassbur (Cenchrus incertus), tumblegrass (Schedonnardus paniculatus), purpletop, Johnsongrass (Sorghum halepense), and tumble windmillgrass (Chloris verticillata) were all common (and most are visible in the slide). Saw greenbriar (Smilax bonanox) is clearly the dominant shrub (not the place for a trail ride) followed by the associate shrub, smooth sumac (Rhus glabra), and scattered chittamwood or gum-elastic (Bumelia lanuginosa). Tree species in order of dominance: post oak and blackjack oak (dominants), live oak (an infrequent associate), and mesquite (rare).   

As a University of Nebraska-produced Ph. D. (a student of John E. Weaver and disciple of F.E. Clements) E.J. Dyksterhuis (1948, ps. 372-374) generally regarded the potential vegetation of the Westerrn Cross Timbers as a climatic climax of oak-little bluestem and Indiangrass understory savannah. That form was shown in some of the preceding slides. Dyksterhuis was unsure how to interprete the Cross Timbers vegetation on Red and Yellow Podzolic soils (p. 373). It seemed logical (rather undeniable in fact) to the current author that such vegetation was a mixed understory of shrubs and grasses (tall, mid- and short grasses) with a woodland-like canopy of scattered oaks of smaller mature size than those of grassland savannas. This seemed the only rational explanation given that the Cross Timbers oak scrub type known as Sand Rough (see under Shrubland slides) exist as postclimax at one extreme of dominance by woody species while the woodland form of savanna exist at the extreme of least coverage of woody plants. Furthermore this must be combined with the historic accounts of tangled woody undergrowth prior to overgrazing by livestock (ie. in the virgin vegetation).

16. Forest form of Western Cross Timbers (Texas)- Exterior view of the forest-like expression of post oak-dominated Western Cross Timbers. These large post oaks have a well-developed tree-form resulting in a physiogonomy and architecture that resembled an actual forest or, at least, a woodland rather than the savanna form or physiogonomic expression more common of the Cross Timbers. Equally, if not more importantly, the trees were large (by post oak standards) and not distinguished by twisted and broken limbs. Trees with these features (ie. “normal trees”) stood in rather stark contrast to the stunted or more-or-less depauperate form of post and blackjack oaks that are thought of as more characteristic of old-growth specimens. In one of the earliest reports on the Cross Timbers of Oklahoma Bruner (1931) described described the trees as “… a scrubby growth of oaks…” (p. 142). Bruner (1931, p.146) presented a photograph of a stunted post oak and described it as “showing the typical growth-form in the savanna”. He wrote that on uplands post oak was “… always small or of moderate stature”. Dyksterhuis (1948, p.333) quoted from a report in 1841 that described the trees as “principally small gnarled” and Dyksterhuis (1948, p. 337) remarked that “timber of log-size “ was at time of his monograph restricted to flood plains. Diggs et al. (1999, ps. 46-48, Fig. 20, p. 49) and Francaviglia (2000, ps.38-40) described the general shape and dimunitive size of post and blackjack oaks.

The trees shown here were massive by Cross Timbers standards and were included to enable viewers to appreciate the size and age to which trees of this savanna type can grow. Viewers should take careful note of the relative great height at which limbs come off the bole. Dyksterhuis (1948, p. 333) wrote that the “oldest ranchers” he spoke with recalled that fires in the tallgrass understory of Cross Timbers “burned the limbs off the trees to a height that enabled a man on horseback to ride beneath their crowns”. Viewers could also note to advantage the horizonal orientation of limbs (and even secondary branches) on these ancient post oaks. Such morphological features clearly indicated the absence of a competing woody understory throughout most of the long lives of these patriarchs. Recent fires have not run through this old stand of monarchs and a woody understory developed instead of the climax herbaceous understory dominated by little bluestem and Indiangrass. Most tragically, an understory of young Ashe or blueberry cedar has formed under the mighty post oaks due to the the “toilet habits’ of birds that perched in the canopy and fire exclusion practices (or the neglect of prescribed burning) of contemporary agricultural man. Blueberry juniper is a nonsprouting species. In the days before man, and later when the red man had the Cross Timbers to himself, natural fires and/or those set in aboriginal wisdom would have taken proper care of the bloody invading blueberry. Now this coniferous pest can grow to heights that will form a fire staircase and generate such intense heat as to threaten the robust and ancient post oaks.  

The species present in this outer or physiogonomic view were given immediately below with the next slide which is an “inside look” at this same local community.

17. Interior of the forest form of Western Cross Timbers (Texas)- A view inside the post oak- dominated forest form of the Western Cross Timbers. Cedar elm (Ulmus crassifolia) was the associate tree species with red mulberry (Morus rubra) running a “close second”. Some sugarberry (Celtis laevigata) was also present. Blackjack oak was absent from this local community, but there were occasional (scattered) large specimens of Texas red oak, also known variously as Shumard or Spanish oak, (Quercus shumardii). Dominant understory shrub was Carolina buckthorn or Indian cherry (Rhamnus caroliniana), but in some areas red haw (Viburnum rufidulum) was locally dominant. (The shrub with the extremely crooked trunk at far right foreground is a red haw.) Green briar or, variously catbriar or bullbriar, (Smilax bonanox) formed a layer with leaves extending both below the trunk and above the crown of the Carolina buckthorn, but the latter appeared to exceed the former in cover. Other shrub species included poison oak, redbud, smooth sumac, skunkbush sumac, spring herald, known also as elbow-bush or devil’s elbow, (Forestiera pubescens), and chittimwood (Bumelia lanuginose), but these were restricted primarily to edges where Cross Timbers came into contact with the interspersed mosaic of Grand Prairie tallgrass prairie and small openings in the Cross Timbers. Community. Shade from the unnaturally high rate of regeneration of oak, elm, mulberry, and, sometimes even, sugarberry plus greenbriar, buckthorn, and red haw had effectively excluded all but relicts of the climax tallgrass. The dominant tallgrass climax species was little bluestem with Indiangrass, upland switchgrass, and big bluestem the other decreasers that occurred (in approximately that order). Some Canada or nodding wildrye, another decreaser, was present. The most common grass was purpletop, an increaser. Grasses were most common on small local areas in association with shrubs, especially where shrub cover was sparse. Forbs were not common, but the perennial herbaceous species known variously as Louisiana (or Mexican or white) sagebrush or western mugwort (Artemisia ludoviciana var. mexicana) was the major one.

Dykesterhuis (1948, ps. 342-343) characterized this as the Quercus-Smilax type of the Western Cross Timbers. This type with designation based on name of dominant Genus of the canopy and of the woody understorey (a Texas version of habitat type that preceeded that of Daubenmire perhaps?) was not adequate by itself to communicate this community. The same designation also described the vegetative or physiogonomic character of the scrub form (the thicket or the tangle) of Cross Timbers that was shown and discussed earlier. The composition (species make-up, physiogonomy, layering etc.) of this forest form differed substantially from the previously shown and discussed oak-greenbriar subtype. Most importantly, buckthorn and red haw were absent from the scrub or thicket form shown above. Perhaps most diagnostic among differences was that the Texas red (=Spanish or Shumard) oak was a shrub (at best a small tree) form with short stature and multi-trunk morphology in the thicket or tangle form whereas here in the forest form or subtype of Cross Timbers Shumard oak grew in a tree form sometimes exceeding the large post oaks in stature and trunk diameter. For example, the large tree with tall forked bole in right background was a Shumard oak. The oak-greenbriar thicket  (scrub) subtype or form had much greater species diversity and development of tree, shrub, and herbaceous layers.

18. Detail view of interior of post oak-dominated forest form or subtype of Western Cross Timbers (Texas)- This photograph showed detail of the local Cross Timbers community shown in the two preceding slides. The two large trees in foreground (left with straight bole and right with large limbs diverging from bole) were post oaks. The two small trees with light-colored bark immediately behind but to right of the widely branching big post oak were red mulberry. The larger background tree on left was post oak and the two smaller trees immediately to right of it were cedar elm. Local understory was all woody and comprised mostly of greenbriar. None of the climax tallgrass understory species were visible within camera range of this photograph, but some shade-stunted specimens of such species as little bluestem, Canada wildrye, Indiangrass, and purpletop were present in this local community.   

19. Cross Timbers and Barrens- Landscape scale view of Western (Upper) Cross Timbers existing as a "patchwork" pattern of woodland and glades or balds. The Cross Timbers and adjacent prairies (delineated variously into such units as Fort Worth, Grand, and Northcentral Prairies) are typically interspersed into a mosaic of vegetation varying from open tallgrass prairie to dense oak-hickory (black hickory and pecan) forests with a savanna form made up of these two extremes plus an open, grassy understory woodland between. A much less common form or expression of vegetation in this "botanical mixture" consist of small glades or balds occuring on hilltops with very shallow soils underlaid by the defining sandstone formations. These sandstone barrens are similar to the chert and dolomite glades interspersed among the oak-hickory forest and tallgrass prairies of the Ozark Plateau several hundred miles eastward (presented below in this Tallgrass Savanna section).

Vegetation shown here was photographed from one such sandstone glade with another such barrens visible in center background. Sandstone balds occurred as vegetational subunits within the overall Sandstone Hills range site presented here and in the following series of photographs taken in or adjacent to Lake Mineral Wells State Park. This was in one of the more distinctive areas of the Cross Timbers delineated by it's rugged, broken topography and exposed sandstone and shale rocks and identified as the "Palo Pinto Country" (Diggs et al, 1999, ps. 22, 45-46). Descriptions of vegetation accompanied those examples.

20. Canyon landform of Cross Timbers and Barrens- Vernal aspect (March) of the same vegetation at same precise location as shown in the immediately preceding photograph except from slightly different angle and at wider lense view. From this vantage point the canyonlands form of the "Palo Pinto Country" Cross Timbers was readily shown. The climax plant community of the "bald" (barrens) atop the characteristic sandstone excarpment in background was shown in detail below. In the present photograph the vegetational mosaic at landscape scale was evident. The view was from one sandstone block photographed across the canyon to another sandstone bloc, each the parent material and lithosol for the local "barrens" or "balds" range site (essentially a larger microsite) within general Sandstone Hills range site. Canyon bottom was a more mesic localized microhabitat favoring cedar elm and Texas ash over the dominant oak species.

The large sparsely foliated tree in center midground was cedar elm as was snag in left front of it. A large Texas ash was immediately to right of large cedar elm. Tree immediately right of Texas ash was also cedar elm. These two species were associates to post oak, the overall dominant species, and to blackjack oak, the dominant vascular plant on the "balds" (shown below).

25. Sandstone glade in Western Cross Timbers- The rugged terrain and harsh nature of the "Palo Pinto Country" West Cross Timbers included local sites (larger microsites) with soils that were somewhat better developed (apparently older) than the rock outcrops responsible for the sandstone barrens vegetation shown in the three immediately preceding photographs. Vegetation in this photograph was conterminus with the plant community (ies) seen in these preceding slides.

This vegetation was climax (in the virgin state) except for woody species that were invading due to absence of fire (fire suppression) on this Texas state park. Fire was a natural component of the climate that contributed greatly to development and maintenance of the Cross Timbers. Woody invaders in this photograph included chittamwood, gum-elastic, or gum bumelia (Bumelia lanuginosa); greenbriar; netleaf hackberry or sugarberry (Celtis reticulata= C. laevigata var. reticulata), redberry cedar or redberry juniper (Juniperus pinchotii); and blueberry cedar or ash juniper (J. ashei). Dominant herbaceous species were little bluestem, sideoats grama, and purpletop. Both woody and gramineous species are native and part of the climax or potential natural vegetation, but the unnatural increase of shrubs and trees was obviously primarily a result of elimination (at least great reduction) of natural fire regimes. Presence (and relatively large populations) of climax dominants (decreasers like little bluestem) coupled with absence of any appreciable component of herbaceous invaders (eg. purple threeawn) or hardly even increasers (eg. purple dropseed) was evidence against current, or even recent, overgrazing. Nonetheless, abnormal increase (invasion) by woody plants was causing on-going range retrogression. Underburning was a principal cause of range depletion.

Parker County, Texas. March (vernal aspect).

Next slide, please.

26. Overgrazed sandstone glade- The vegetation shown here was on private property contiguous with that seen in the immediately preceding photograph. The plant community seen in this slide was being (or had very recently been) overgrazed. Prolonged or longterm overuse had resulted in depletion of the more palatable little bluestem, purpletop, and sideoats grama and commensurate invasion by purple threeawn (the conspicuous tufts of bunchgrass) and increases in purpleflower droopseed (predominate plant among clumps of threeawn).

Invasion of the same woody species as in the preceding slide was evident along edges of the glade as an advancing line of young shrubs that was reducing the area of the herbaceous plant community. Fire cessation was also a factor in this invasion, but in addition to underburning overgrazing was an agent of retrogression that induced range depletion in this instance.

Parker County, Texas. March (vernal aspect).

27. Climax sandstone glade in Western Cross Timbers- Two views of a sandstone glade in excellent range condition situated among adjacent tracts of blackjack oak-dominated woodland characteristic of Western (Upper) Cross Timbers. This vegetation was on a hilltop portion of Cross Timbers having more of an open woodland physiogonomy that had a "tangled" understorey consisting of a woody layer of shrubs dominated by young (immature) blackjack and also including young post oak, cedar elm, sugarberry or netleaf hackberry, and such shurb species as saw greenbriar, winged sumac (Rhus copallinum var latifolia), skunkbush sumac, and chittamwood, and an herbaceous layer dominated by little bluestem.

Woody species were noticably less abundant than on adjacent glades shown above including the one that had been been subjected to recent or current overgrazing.

Parts of the sandstone balds or barrens were devoid of woody species (especially the glade form) and had a more species-rich herbaceous community. Little bluestem was the most abundant species but there was not an apparent dominant. The other common grass species on the balds were: green sprangletop (Leptochloa dubia), sand lovegrass (Eragrostis trichoides), and sideoats grama on the shallower microsites in central portions of the glade and tall dropseed (Sporbolus asper) , Texas wintergrass (Stipa leucotricha), purpletop, Scribner's panicgrass (Panicum scribnerianum), Canada wildrye, and wood oats (Uniola latifolia= Chasmanthium latifolium) along perimeter of the glade and beneath or otherwise in shade of trees. The conspicuously dominant forb was slender bushpea or slender lespedeza (Lespedeza virginica).

28. Shown below was a series of photographs of Western Cross Timbers in relict or near relict climax condition. The sequence began with an exterior view and consecutive photographs showed progressively more interior views of relatively undisturbed old growth Cross Timbers vegetation. Exclusion of fire by policy and action of a state government agency allowed unnatural excessive development of woody species in the understorey with concomittant decline in the herbaceous component (primarily of little bluestem, the dominant, and also of other grasses such as purpletop, the associate herbceous species, sideoats grama, wood oats, tall dropseed, Canada or nodding wildrye, Texas wintergrass, and even small amounts of big bluestem and Indiangrass).

Composite view of Western Cross Timbers community- An exterior perspective of a virgin stand of post oak-dominated Cross Timbers with a rich diversity of species in all vegetational layers. The foreground was edge of a small opening or glade dominated by little bluestem accompanied by purpletop, wood oats, tall dropseed, Scribner's panicgrass, with traces of big bluestem and Indiangrass in lower (more mesic) microsites at far right foreground. Englemann or Lindheimer (sometimes Texas or nopal) pricklypear (Opuntia engelmannii var. lindheimeri) was conspicuous in the glade (left-center foreground). Most apparent forb was goldenrod (Solidago sp). The young tree or shrub appearing as a bush at far left foreground was blackjack oak showing regeneration of this climax species and illustrating fact that blackjack not post oak tends to dominate on the shallower soil of glades. The large tree with brightly colored leaves at right forefront of tree edge was Texas ash (Fraxinus texensis= F. americana var. texensis). The most common shrub in understorey beneath trees was saw greenbriar. October, but still estival aspect.

Stand of old growth post oak-dominated West Cross Timbers- On this sandstone rock outcrop the habit of mature (nearly ancient in relative terms) post oaks created the physiogonomy characteristic of the climax forest form of Cross Timbers. This was an example of the Quercus-Smilax type of the Main Belt described by Dyksterhuis (1948, ps. 340-342). The conspicuous rounded shrub in center foregrounmd was elbow-bush, devil's-elbow, or spring-herald which is typically more common on calecareous soils and among limestone more than sandstone outcrops. Englemann pricklypear was also conspicuously growing at edge of forest and a grass-dominated glade. The understorey inside the forest itlself (beneath trees and not natural clearing or glade) was primarily regenerating post oak and saw greenbriar. Grass species visible at edge of forest and glade (center foreground) was silver bluestem. October, but still estival aspect.

Interior of old growth West Cross Timbers forest community- It was noted at beginning of the Cross Timbers section that this forest or range type was primarily a savanna, but that vegetation was a continuum which varied from grassland with widely scattered (isolated) trees to dense forest and with intermediate types of such canopy cover as to form woodland and savanna forms of the general Cross Timbers cover type. The photographs included in this present series illustrated the forest form. Post oak was the dominant form with blackjack the clear associate. In this slide blackjack was represented by the the second tree trunk from the right and the smaller trunk at far left (leftmost tree). The pronounced horizonal branching of trees that grew in more open woodland was prominent in the limbs of the largest tree, a post oak, in center of slide. The pronounced outward (toward light) curving of the bole (bow-shaped trunk) of the blackjack was another common growth mainifestation of old- growth oaks (in woodland and even savanna forms as well as in forest canopy cover forms).

The understorey was almost exclusively post and some blackjack oak reproduction. Oak leaves formed a forest floor covering interrupted only by standstone rocks. There was essentially no herbaceous undergrowth. Saw breenbriar was sparse and limited to small areas where light could penetrate through the oak canopy to reach the ground surface. Rarely there were other species of woody vines as shown and described in the succeeding photograph and caption.

Lichens growing on the outcropping sandstone rocks formed a layer of vegetation that students should not overlook.

Estival aspect into early October.

Deep inside a Cross Timbers forest on a sandstone outcrop- Narrow spaces of soil among huge sandstone boulders (as large as small houses) provided favorable environments for growth of Cross Timbers trees. Post and blackjack oaks were dominant, but sugarberry or hackberry, Texas ash, and cedar elm were also common. Climbing species were, as shown here, abundant. The thicket-like growth in the left foreground was a mixture of saw greenbriar, supplejack or rattanvine (Berchemia scandens), and poison ivy or oak. Other common vines found variously in the boulder location were Carolina snailseed (Coccus carolinus), Virginia creeper, trumpet-creeper (Campsis radicans), and, infrequently, mustang grape (Vitis mustangensis). This boulder form or expression of a Sandstone Hills range site had so much shade from tree canopies and the vertical rock formation that herbaceous species were more-or-less absent.

October, but still estival aspect.

Not enough fire- Most of the early explorer accounts of the Cross Timbers (including the poetic account of Irving [1835, p. 186] quoted above) and the seminal ecological studies (eg the monograph of Dyksterhuis [1948, p. 333] also cited previously) specifically described presence and/or role of fire in understorey of the Cross Timbers.Fire had obviously been excluded and suppressed-- and obviously for a long time period-- from the state park in which these photographs were taken. Long-term absence of fire, a natural environmental factor, from this Cross Timbers vegetation had allower development of an unnaturally dense woody understorey which had eliminated most of the native herbaceous species except for small microsites. An excample of one such microhabitat was that shown here around an older post oak. Little bluestem, the dominant herb and co-dominant Cross Timbers species (with co-dominant post oak), had persisted on this local site (and others like it). Even here brush (woody species present at unnaturally excesssive cover and population densities) were encroaching on the limited remaining microsites that afforded adequate sunlight and growing spaces. Most of the woody (and excessive) understorey was of post and blackjack oak, but other tree and shrub species were also present. Chief among these was saw greenbriar and chittamwood or bumelia.

General co-dominants of the Cross Timbers- Post oak (larger tree with twisted limbs at left background) and blackjack oak ("runt"-- as in scrubby-- trees at right) are the general two dominants of the Cross Timbers. Post oak is far and away the clear dominant with blackjack subordinate so as to be more of an associate, except that blackjack-- often as shrub or small tree more than true arboreus form-- is the exclusnve dominant on the more xeric sites and microsites such as the balds or barrens form of Crosss Timbers.

The shrub layer of Cross Timbers understorey was conspicuous in this photograph due to showy full-bloom phenological stage of creek or hog plum (Prunus rivularis). The two oak species were also in anthesis.

Western Cross Timbers in the spring- Thickets of blooming hog or creek plum highlighted the shrub layer of an understorey beneath the dominant species of post oak (tree with the sparse foliage of new leaves and catkins in right background) and blackjack oak (largest tree in center foreground and branches at far left foreground. Chittamwood or gum-elastic and Carolina buckthorn (Rhamnus caroliniana) were also present as understorey shrubs.

29. One of the key distinguishing (and picutresque) features of the Cross Timbers is the unusual and interesting shape of boles, limbs and branches, crowns, and overall habit or growth form of individual trees of the dominant post and blackjack oaks. These characteristics of distorted tree growth distinguish-- even at first or fleeting glance-- the Cross Timbers expression of the general oak-hickory association or, more precisely, the ecotone between this climax forest type and the tallgrass prairie climax type from the westernmost extension of the actual oak-hickory forest region of Braun (1950, pgs. 35, 162-191). This ultimate authority on the eastern deciduous forest included the Cross Timbers as one part of the "forest-prairie transition" in the oak-hickory region and described the oaks as "usually small and scrubby with broad low crowns" (Braun, 1950, pgs 177-178).

Many, if not most, descriptions of the Cross Timbers characterized the post and blackjack oaks variously as "stunted", "scrubby" or "scrubs", "dwarfish" or "dwarfs", "diminutive", "small-sized", "undersized" "depauperate", etc. More recently-- and perhaps as result of interest in old-growth forests and individual old-growth specimens-- descriptions of relatively small mature trees were more detailed as to specific aspects or parts of small-size and apparent "stunted growth" morphology. From dendroclimatic studies such unique tree habits, crowns, trunk and limb shapes, etc. have been related to harsh physical and chemical features of tree habitat on which slow plant growth rates and distorted tree organs (due perhaps to injury) were associated with old age. Perhaps old age and "abnormal" appearance of trees were results of poor growing conditions such as undernutrition or near constant edaphic drought. Distorted shape and size of organs like boles and limbs might reflect conditions that were below optimum for "normal" growth and reproduction but near maximum for longevity.) Cause and effect relations among the factors of tree age, tree growth, soil conditions, climate (including lightening and fire), browsing, and so forth are not adquately understood.

Diggs et al. (1999, p. 47) described this phenomenon of misshapen, often grotesque, form and diminutive size of old-growth or "ancient" individual trees in the Cross Timbers. These authors cited findings from dendrochronology (tree-ring analysis) and summarized as follows: "Because of the low availability of moisture, rocky or infertile soil, and other factors, the trees of these relict forests, while old, have a slow rate of growth and are of relatively small size... Such old-growth forests or ancient individual trrees can often be located by environmental factors such as steep, rocky, infertile soils or by the appearance of the individual trees... Twisted stems, dead tops and branches, canopies restricted to a few heavy limbs, branch stubs, fire and lightening scars, leaning stems, exposed roots or root collars, and hollow voids are all hints of significtnt age".

Shown below were examples of mature and, quite likely, old if not "ancient" trees growing in the harsh environment of the rugged "Palo Pinto Country" Cross Timbers. Some of these trees had "real character" possessing distinguishing "marks" that obviously resulted from injury (eg. crowns whose tops had been torn off by wind or blown off by lightening, hollows due to rotting following such "amputation", fire scars). Other unusual shapes and sizes appeared to be more the result of inadequate/improper nutrition, including sufficient water.

Readers should bear in mind that this phenomenon of natural bonsai-like growth and aging is not limited to oaks in the Cross Timbers nor to oaks. As shown elsewhere in this publication, dead tops with hollows, spires, cavities and limb loss due to fire or other forces, and relatively small size are characteristics common to old-growth Juniperus trees on pinon-juniper woodland. Neither are such features that are frequent on old trees limited to environments unfavorable for tree growth and survival. Many of the very large (and very old) individuals of the various conifer species that grew to record size, shape, and dimensions (ie. "record", meaning "brag", trees) live on the most favorable, productive sites. The coast redwoods with spire-like dead tops and "goose pen" fire and wind scars are probably most notable among these, but many other examples exist among Sitka spruce, western hemlock, western red cedar, Douglas fir, and even ponderosa pine. It appeared that such scars and marks likely are results of a long life more more than of a hard life.

Whatever the cause-effect relations, many of the Cross Timbers post and blackjack oaks sport natural mutulations that should be the envy of any human specimens vainly flashing tatoos, pierced body parts, streatched necks, embalmed breasts, plasticized penises, corseted abdomens, bustled buttocks, and once-healthy skin now sun-scorched or "fake-baked" to the state of weathered saddle leather or a cancer-eyed cow. The difference between a deformed, hollow old tree and a woman with diamond studs in peirced ears is that the tree has a beauty and dignity all its own. The woman just looks like she was shot with rock salt. Enjoy the examples.

Arborescent goblins- A branching pattern in which primary limbs radiated horizonally from the short trunk with secondary and vertical branching from the primaries gave a hominoid-like appearance to these old Cross Timbers post oaks. Such trees give even the most hardened coon hunter an almost erie feeling as he tromps through these woods under a full moon. One can imagine the spell-like feeling cast on backwoodsmen upon first setting foot in these vast primival savannas.

The featured post oak had lost it's central shoot, including the apically domiant terminal meristem, so that once released from apical dominance secondary branches on the primary limbs grew and developed in neraly vertical planes. The smaller tree with glossy green leaves to left of ole Lost Top was a younger blackjack oak. A young Texas ash was at right base of the topped post oak. Widely scattered shrubs included greenbriar, elbow bush (Foresteria pubescens var. glabrifolia), skunkbush sumac, chittamwood, and Carolina buckthorn. Grasses were absent apparently having been mulched out by accumulations of leaves from the dominant oaks and understorey shrubs as result of unnatural fire exclusion.

"And the gobble-uns'll git ya ef ya Don't Watch Out."--- Little Orphant Annie, James Whitcomb Riley

March: vernal aspect with oaks in full-flower.

Crown development of an old post oak subsequent to death of the central and dominant shoot- For a reason (perhaps injury due to lightening, wind, insects, disease) known but to God the main leader of this post oak died such that relieved from dominance (suppression) by apical meristem lower subordinate limbs and branches developed. Result was a lop-sided crown and another hollow-top tree serving as a cozy den for some varmit like a coon or 'possum. Some such tree become hollow clear to the base of their trunk as the innermost trunk, especially heartwood, rots out. This does not affect living tissue (such central heartwood and older sapwood are dead anyway) nor does it typically affect tree health. Such rotting may eventually contribute to loss of tree rigidity and even tree blow-over if and when decomposition proceeds to the root system, but more commonly impact is neglible.

The reason is a feature of physics that is widely know among mechanical engineers: hollow tubes like bird quills, most grass shoot internodes, pipes, airplane wings, and hollow trees are almost as strong as a solid piece of wood, metal, or feather. And they are much less lighter which allows resources to be used for other tissues or materials (eg. those capable of conducting photsynthesis or holding jet fuel) or for more efficient work (easier and more economical to clear ground or a tree branch for flight). It would even be desirable to construct hollow railroad ties, but the technology to do such does not justify the savings in wood.

The well-developed shrub layer of the understorey was comprised mostly of skunkbush sumac and elbow bush with lesser cover of greenbriar.

March: vernal aspect, full bloom phenological stage in oaks.

Wooden arm with a dozen elbows: growth and branching pattern of post oak on sandstone bald- This microhabitat on an outcropping of sandstone was marginal even for a post oak. Result was that this speciman developed a recurrent geniculate (a back-and-forth bending) shape to it's trunk and branches. The more xeric (or less mesic) blackjack oak is typically dominant on such microsites with their shallower, drier soil. Such was the case seen here where scrub (shrub form) blackjacks surrounded the bent, knarled old post oak. These appeared to enjoy each other's company, but they obviously did not invite any herbaceous species to join their party.

Vernal aspect (March, and under a grand but equally rare cobalt-blue Texas sky).

What tales this ole devil tells- An ancient post oak lost the upper portion of it's trunk complete with crown except for one limb which subsequently sent up a vertical branch to assume role of former main shoot and crown though in a much reduced capacity. Yet another picturesque example of the phenomenon of apical dominance. This magnificent old tree was a real survivor-- complete with sexual reproduction and passing on of it's genes in propaguling acorns . In addition to serving as prime real estate for den-dwelling furbearers this gnarled, weatherbeaten, ranking member of the Cross Timbers community never tires of talking about it's accident or "operation". A passing rangeman paused to record the story and pass it along to fellow students of vegetation and admirers of things beautiful.

Palo Pinto County, Texas. March: vernal aspect.

Breakage in the Oklahoma Cross Timbers- Stand of Cross Timbers dominated by post and blackjack oak in Sandstone Hills of northern Oklahoma shortly after a severe to extreme ice storm from a winter mix of precipitation caused widespread and locally extradinary damage to trees and shrubs. Damage to trees ranged from loss of minor twigs to uprooting with most trees suffering heavy damage with loss of some major limbs total crown loss.

The beneficiaries of such devestation were the understorey species especially the tallgrass species like little bluestem and Indiangrass on this west slope.

Lincoln County, Oklahoma. Mid-December.

Chewed up by ice- Young blackjack oak (first or upper slide) and ancient post oak (second or lower slide) in Sandstone Hills Cross Timbers with extreme ice damage from a late autumn winter storm that brought rain, freezing rain, sleet, and snow which built up to such accumulations (depths of one to four inches) of ice on trees that limbs, large to small branches, and twigs were broken. Some trees like this old post oak (and the ancient post oak presented immediately below) were completely topped with their crowns more broken than Jack when he fell down. Some trees were even toppled by uprooting from heavy ice accumulations.

When rangemen and foresters speak of agents of defoliation the consideration is not limited to grazing/browsing animals. "Fire and ice" along with wind, frost, drought and others keep the Cross Timbers far from being a Garden of Eden, at least from a tree's vantage point. Incidentially, all this ice-downed wood is fuel just waiting for a fire that could be readily ignited by spring thunderstorms that undoubtedly await these survivors. And you thought you had it rough!

Lincoln County, Oklahoma. Mid-December.

"Gittin' old ain't for sissies"- This grand ole patriarch was not favored to live all its "golden years" as "happy times". This ancient specimen was hit by a severe or extreme ice storm a week before these two photographs recorded the tragic event in its long life. A late autumn (9 December, 2007) ice storm (a winter mix of rain, freezing rain, sleet, and snow) struck the Cross Timbers in the Sandstone Hills or northern Oklahoma with the devestation of a twister. This ice storm was due to the phenomenon of overriding, the atmospheric condition that results from the meeting (a collusion) when warm, moist air from the Gulf of Mexico and a cold Arctic air mass (a Norther). The accumulation of ice (up to several inches thick) wrought damage to trees varying from loss of small branches to major limbs to, as in this case, the complete topping of a large tree.

And this might not be the end of the tragedy. The heavy accumulation of downed timber is fuel-loading just waiting for a fire that could be sparked readily from spring thunderstorms ( which in Oklahoma are more numerous and every bit as notarious as ice storms). This senior citizen of the Cross Timbers does not seem destined to meet a mild end to its old life, but stay tuned as we follow its saga.

Lincoln County, Oklahoma. Mid-December.

31. Post oak- Young leaves and catkins of the dominant tree species of the Post Oak Savanna and Cross Timbers of Texas and most of the Cross Timbers Oklahoma into Kansas except on sites dominated by

32. Leaves and fruit of post oak (Quercus stellata)- Characteristic apex of short shoot of post oak showing typical arrangement of an extra heavy crop of acorns. Post oak is a member of the Quercus subgenus Leucobalanus, the white oaks, whose leaf veins do not extend as spines, bristles, or "teeth" beyond leaf margins. Leucobalanus species bear fruit annually (ie. acorns mature in the same growing season) so that acorns are borne on current-season shoots (leaders). The kernal or "meat" of acorns in the white oak subgenus are sweet-tasting (versus the bitter kernals of red or black oaks). Erath County, Texas. October.

33. Post oak acorns- Detail of cup and nut of post oak acorns. Erath County, Texas. September.

35. Normal appearance of leaves and acorn on a leader of blackjack oak- Blackjack is a member of Quercus subgenus Erythrobalanus (red or black oaks) one characteristic of which is extensions of veins or ribs of leaves beyon the margin so as to appear as spines, bristles, opr "teeth". Acorns of Erythrobalanus oaks require two growing seasons for development and maturation. Thus these fruits are borne on twigs (leaders) that were produced during the previous growing season. Meat of the acorn is bitter or tart-tasting. Erath County, Texas. October.

36. Blackjack (Quercus marilandica) branch-Lateral shoot of blackjack oak with leaves and fully mature fruit. Erath County, Texas. October.

37. Leaves and acorn (at full maturity) of blackjack oak- Detail of ripe acorn and two leaves of blackjack oak. Erath County, Texas. October.

38. Texas ash tree (Fraxinus texensis= F. americana subsp. texensis) in spring uniform- This ash was the one featured above in photographs that showed a composite of the Western Cross Timbers old-growth community. This tree was in the immediate pre-bloom phenological stage and with the bright, glossy, young leaves that are characteristic of deciduous species in the Cross Timbers during spring before months of hot Texas sun turns them a dark forest green.

39. Shrub form of Texas ash- Multiple-boles (shoots or trunks) and relatively small stature of this Texas ash qualified it as a example of the shrub form of this species. This and the preceding photograph provided instructive examples of the distinction-- and often an arbitrary one-- between tree and shrub, a beginning lesson for students in the Principles & Practices of Range Management course. Learn the lesson.

42. Glossy new leaves of cedar elm (Ulmus crassifolia)- A branch and spring leaves of this Cross Timbers associate species had the shinny, waxy coat of newly expanded foliage that is characteristic of Texas trees and shrubs before the brutal heat of a long, baking summer takes it's toll.

43. Dogwood of the Cross Timbers- Roughleaf or Drummond's dogwood (Cornus drummondii) is a widely distributed "kissin' cousin" of the better-known flowering dogwood (C. florida). Roughleaf dogwood has much smaller flowers (shown below) and is better adapted to harsher habitats than its more mesic and florally endowed "cousin". For example, roughleaf dogwood is native to roughly the eastern half of the Lone Star Star so as to grow far west of flowering dogwood. Roughleaf dogwood is the Cornus species that is common in the Cross Timbers and Prairies vegetational area of Texas as well as northward through central Oklahoma and as far north as South Dakota. This is also the most widely distributed dogwood throughout the both the tallgrass and mixed prairies of the Central Lowlands physiographic province (McGregor et al., 1977, ps. 204-205).

Roughleaf dogwood was introduced as an important and common shrub on moister environments of the central grasslands of North America, understorey woody plant in Cross Timbers and local bottomland forest communities, and member of savannahs and general ecotones among grassland and forest range types. Roughleaf dogwood is also an major species in local postclimax communities within more general and larger range plant communities (macro-communities) as for example sandrough scrub in the West Cross Timbers.

The pretty specimen shown here was adding beauty to the understorey of a stand of post oak-dominated West Cross Timbers. Erath County, Texas. Late May. Full-bloom phenological stage.

44. A pack of dogwood flowers- Flower cluster of roughleaf dogwood. These examples were from a sandrough range type, a deep sand habitat existing as postclimax (monoclimax theory) or edaphic climax (polyclimax theory) with the greater West Cross Timbers.

Erath County, Texas. April.

46. Buckthorn or Carolina buckthorn (Rhamnus caroliniana= Frangula caroliniana)- Ths shrub is a distinctive understorey species of the Cross Timbers. Cross Timbers vegetation is, of course, the western-most extension of the oak-hickory forest. It was assigned to the Oak-Hickory Forest Region as a forest-prairie trnaistion by Braun (1950, p. 177). Carolina buckthorn appears to have an ecological niche and role in the Crosss Timbers similar to that of redbud and flowering dogwood in the main body of the oak-hickory forest types. Braun (1950, p. 153) listed R. caroliniana as being associated with redbud, dogwood, common persimmon, southern buckthorn (Bumelia lycioides), and skunkbush sumac on more xeric sites in the Western Mesophytic Forest Region. In his classic description of the Western Cross Timbers (Dyksterhuis (1948, Table 2, p. 341 and Table 3, p. 342) listed skunkbush sumac and false or wooly buckthorn, chittamwood or chittam, gum bumelia, gum elastic (Bumelia lanuginosa), but strangely did not list or even make passing reference to Carolina buckthorn.

47. Leader with leaves and fruit of Carolina buckthorn- The drupes of this species turn a bluish black at maturity. The fruitsin these examples were in the pinkish-red, pre-mature stage (and that is sometimes as far as they progress before birds, squirrels, and other wildlife species facilitate a p