ILLUSTRATED FLORA OF EAST TEXAS - Brit - Botanical Research ...

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POST OAK SAVANNAH/INTRODUCTION 109 FIG.65/STANDARD/TRADITIONAL DELINEATION OF WEST GULF COASTAL PLAIN VEGETATIONAL AREAS AND BOUNDARY (DASHED LINE) OF THE WEST GULF COASTAL PLAIN PHYTOGEOGRAPHIC PATTERN (MACROBERTS ET AL. 2002C). MODIFIED FROM MACROBERTS ET AL.(2002C) AND MACROBERTS AND MACROBERTS (2003A), WITH PERMISSION OF MICHAEL MACROBERTS AND THE BOTANICAL RESEARCH INSTITUTE OF TEXAS. a number of past workers who also pointed out the lack of a sharp boundary between the Pineywoods and Post Oak Savannah. For instance, Tharp (1926) indicated that the transition to the Post Oak Savannah “…merely means the gradual decrease of pine until it has disappeared.” Another example is McCarley’s (1959) statement that the “boundary between the pine-oak region and the oak-hickory region is nowhere sharply marked, but is characterized by a gradual decrease in pine and an increase in oaks and hickories.” In other words, “there is no floristic break … or unique communities by which the [Post Oak Savannah] can be described” (MacRoberts & MacRoberts 2003a). However, it can be argued that in many if not most cases that adjacent vegetational regions lack sharp boundaries (e.g., Edwards Plateau and South Texas Plains). It cannot be overemphasized that despite the seemingly sharp breaks indicated on vegetational maps, vegetational transitions are rarely sharp or well-defined—the Post Oak Savannah-Pineywoods transition is just one example of this phenomenon.
110 INTRODUCTION/GEOLOGY AND SOILS OF POST OAK SAVANNAH Nonetheless, the lack of the ability to draw an exact line of demarcation between two areas does not mean that major differences do not exist. While the Post Oak Savannah is closely linked floristically and ecologically to the Pineywoods and the rest of the West Gulf Coastal Plain, it is known that the Post Oak Savannah did have extensive areas of savannah that differed greatly in aspect from the Pineywoods. Even today, the overall appearance of the Post Oak Savannah is quite different, and most areas of Post Oak Savannah can be easily distinguished vegetationally from most areas of Pineywoods. Not only are the two areas largely different both in their original and modern day vegetational cover (Post Oak Savannah with more grasses, fewer trees, and pines mostly restricted to the eastern edge)—they also differ in terms of soil and rainfall. These differences were reflected in the quite different land use histories following European settlement: lumbering in the Pineywoods versus row cropping and ranching in the Post Oak Savannah. Thus, while these two parts of the West Gulf Coastal Plain share many similarities and have an indistinct boundary, recognition of two distinct areas is a useful, practical, and vegetationally accurate distinction. As a result, and following traditional practice in Texas, we believe it is appropriate to continue to recognize the Post Oak Savannah as a separate vegetational area. While vegetational similarities exist throughout the Post Oak Savannah, there are numerous local differences. For example, the northeast portion is considerably wetter than the less mesic and warmer southwest, with significant impact on the vegetation—e.g., more Quercus falcata (southern red oak) in the northeast, in contrast to Quercus virginiana (live oak) in the south. Likewise, there is a narrow band of vegetation, found on the primarily sandy alluvial soils adjacent to the Red River in the northernmost portion of East Texas, that we are referring to as the Red River Area. Some of the Red River Area has traditionally been treated as part of the Post Oak Savannah, while the westernmost portion (northern Grayson County) has typically been classified as part of the somewhat similar Cross Timbers and Prairies (Correll & Johnston 1970; Hatch et al. 1990). While similar in many respects to the Post Oak Savannah and reasonably included in that category, the Red River Area differs significantly and is therefore discussed separately here as a distinct vegetational area (see page 127). From a conservation perspective, MacRoberts and MacRoberts (2003a) point out that the manner in which ecological boundaries are drawn can have significant implications. “For example, Ricketts et al. (1999a) concluded that the OPH [Oak-Pine-Hickory] plus LLP [Longleaf Pine] ecoregions (their ‘Piney Woods Forests’) had only 7 endemic plants and the POSa [Post Oak Savannah] region (their ‘East Central Texas Forests’) also had only 7 endemic plants. However, by combining the POSa, OPH, and LLP regions, we calculate that these three ‘regions’ together have approximately 100 endemic or near-endemic plants, not 14!— thereby instantly changing the WGCP [West Gulf Coastal Plain] from an ecological cold spot to an ecological hot spot” (MacRoberts & MacRoberts 2003a). Such an example points to the critical need for further study and a better understanding of the flora of many areas. GEOLOGY AND SOILS OF THE POST OAK SAVANNAH As discussed in the general sections on geology and soils of East Texas, the Post Oak Savannah has developed on sedimentary substrates of Tertiary age. The soils, developed from sandstone rocks of such geologic layers as the Carrizo and Wilcox, can be generally described as sandy (Sellards et al. 1932; Hartmann & Scranton 1992). More specifically, they are usually acidic, with sands and sandy loams occurring on the uplands and clay to clay loams on the bottomlands (Texas Parks and Wildlife 2002a). Often, but not always, a dense clay pan is present at a lower soil horizon. Because of this phenomenon, the Post Oak Savannah is sometimes referred to as the “Clay Pan Savannah.” These clay pans, underlying the surface layers of the soil, are nearly impervious to water. As a consequence, the moisture available for plant growth is limited to that in the upper soil horizons—the result is that much of the Post Oak Savannah can be a “droughty” and surprisingly arid habitat at times (Texas Parks and Wildlife
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ILLUSTRATED FLORA OF EAST TEXAS
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ALLDREDGE, LINDA & JACK BATTERBAE,
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We would like to recognize and expr
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ISSN 0833-1475 ISBN 1-889878-12-X S
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“DEEP EAST TEXAS IS AN OLD, QUIET
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Elray S. Nixon E lray Nixon was bor
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ILLUSTRATED FLORA OF EAST TEXAS TAB
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TABLE OFCONTENTS/ PAGE APPENDICES A
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Hymenocallis liriosme
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ILLUSTRATED FLORA OF EAST TEXAS OVE
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4 INTRODUCTION/GEOGRAPHIC AREA OF E
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10 INTRODUCTION/MAJOR RIVERS OF EAS
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12 INTRODUCTION/PLANTS TREATED The
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14 INTRODUCTION/GUIDE TO ARRANGEMEN
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16 INTRODUCTION/GUIDE TO SOURCES OF
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18 INTRODUCTION/GUIDE TO GEOGRAPHIC
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20 INTRODUCTION/GUIDE TO ENDANGERED
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22 INTRODUCTION/GUIDE TO GLOSSARY,
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24 INTRODUCTION/GUIDE TO ABBREVIATI
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26 INTRODUCTION/SUMMARY DATA ON FLO
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28 INTRODUCTION/ACKNOWLEDGMENTS Kar
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30 INTRODUCTION/AUTHORS’ NOTE Pre
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32 INTRODUCTION/GENERAL GEOLOGY OF
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46 INTRODUCTION/SOILS SOIL ORDER DE
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48 INTRODUCTION/SOILS, EAST TEXAS B
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50 INTRODUCTION/SOIL-RELATED GEOLOG
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Page 75 and 76: 58 INTRODUCTION/SOIL-RELATED GEOLOG
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Page 95 and 96: 78 INTRODUCTION/GEOLOGY OF PINEYWOO
Page 97 and 98: 80 INTRODUCTION/PRESETTLEMENT, EARL
Page 105 and 106: 88 INTRODUCTION/PRESETTLEMENT VEGET
Page 107 and 108: 90 INTRODUCTION/CURRENT VEGETATION
Page 123 and 124: 106 INTRODUCTION/POST OAK SAVANNAH
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Page 129 and 130: 112 INTRODUCTION/SOILS, FIRE, AND T
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Page 135 and 136: 118 INTRODUCTION/VEGETATION OF POST
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Page 143 and 144: 126 INTRODUCTION/POST OAK SAVANNAH
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Page 147 and 148: 130 INTRODUCTION/BLACKLAND PRAIRIE
Page 149 and 150: 132 INTRODUCTION/GEOLOGY OF BLACKLA
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Page 163 and 164: 146 INTRODUCTION/FUTURE OF BLACKLAN
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Page 171 and 172: 154 INTRODUCTION/PRESENT AND FUTURE
Page 173 and 174: 156 INTRODUCTION/BIG THICKET THE BI
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160 INTRODUCTION/NATURAL HISTORY OF
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172 INTRODUCTION/SUMMARY DEFINITION
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174 INTRODUCTION/PRESETTLEMENT AND
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184 INTRODUCTION/HISTORY OF BIG THI
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190 INTRODUCTION/CONSERVATION IN BI
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200 INTRODUCTION/ORIGIN AND DIVERSI
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228 INTRODUCTION/CONSERVATION IN EA
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234 INTRODUCTION/HISTORY OF BOTANY
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244 INTRODUCTION/BOTANY IN NORTH CE
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246 INTRODUCTION/BOTANY IN NORTH CE
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248 INTRODUCTION/BOTANY AT UNIVERSI
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250 INTRODUCTION/BOTANY AT TEXAS A&
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252 INTRODUCTION/BOTANY AT TEXAS A&
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254 INTRODUCTION/OTHER CONTRIBUTION
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256 INTRODUCTION/CURRENT BOTANICAL
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258 INTRODUCTION/BOTANICAL ART IN E
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