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

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NATURAL HISTORY OF BIG THICKET/INTRODUCTION 163 larger areas of beech-magnolia-loblolly forests (e.g., in the Beech Creek Unit of Big Thicket National Preserve) but fewer areas dominated by longleaf pine (Harcombe et al. 1993). Because the Willis is well-drained, wetland communities are in general restricted to stream bottoms or to Wet Herbaceous Seeps/hanging bogs on hillsides (Watson 1975). Still further south, on the Pleistocene Lissie (including the Bently and Montgomery) Formation, xeric sandylands and longleaf pine uplands can be found on higher, dry sandy terraces between the streams, or in the case of longleaf pine, on mounds on the nearly flat savannah wetlands. In general though, the Lissie and the still younger Beaumont (also Pleistocene) (e.g., near Beaumont and Little Pine Island Bayou) underlie very flat areas close to sea level—hence they have a high water table and are more subject to flooding and water retention. In addition, the soils of the Lissie and Beaumont formations have a higher clay content, particularly in the subsoils. These soils are thus less permeable and often poorly drained, favoring plants with greater water requirements or tolerance. Wetland communities such as palmetto-hardwood flats, wetland longleaf pine savannahs, and bald-cypress sloughs are common in this flat terrain (Smeins et al. 1982; Bridges & Orzell 1989b; Parent 1993). Even here, slight differences in topography and soil moisture—such as mima mounds (see page 65), old terraces, or slightly higher areas between streams—can have a major impact on the plant species present. For example, on the Beaumont Formation, longleaf pines are essentially restricted to mima mounds (Watson 1975). On the very southern edge of the Big Thicket, on the Beaumont, wetland longleaf pine savannahs and scattered areas of prairie are transitional to what was in presettlement times a large expanse of Coastal Prairie, underlain in general by clay soils. Two other cases further exemplify the influences of soil, topography, and hydrology on vegetation. Particularly interesting are areas where tight impermeable clay soils and flat terrain result in very poor drainage and standing water during part of the year. Such areas are known as Wet Pine Savannahs or savannah wetlands (see page 97). The growth of woody plants in these areas is apparently retarded by waterlogging and high acidity. In addition, because of their slow growth, trees in such areas are vulnerable to fire for relatively longer (MacRoberts & MacRoberts 1993a; 2001). Also, Wet Pine Savannahs have soils that tend to be acidic and very poor in nutrients, and carnivorous plants do well—in fact, 14 species in four different genera, Sarracenia (pitcher plants), Drosera (sundews), Pinguicula (butterworts), and Utricularia (bladderworts), are found in East Texas. As with all carnivorous plants, nutrients (especially nitrogen), rather than calories, are obtained through carnivory— these plants still obtain the energy they need for growth and development through photosynthesis. In contrast to the poorly drained Wet Pine Savannahs, the excessively drained, dry, white quartz sand soils of the Dry Uplands on Deep Coarse Sands (also known as xeric or arid sandylands) (see page 92) support such dry-adapted plants as Cnidoscolus (bull-nettle), Opuntia (prickly-pear), Quercus incana (bluejack oak), Vaccinium arboreum (farkleberry), and Yucca. Factors affecting succession have long been important in influencing the vegetation of the Big Thicket (and much of the southeastern United States). These include such diverse phenomena (at widely varying scales) as recurrent hurricanes, special edaphic conditions, beaver activity, oxbow lake formation, the gradual filling of bogs, and fire. Of all of these, fire is probably most important. According to MacRoberts and MacRoberts (2000), “about half of the plant communities of the Longleaf Pine Ecoregion require periodic fire or they gradually succeed to other communities, losing key species and structural integrity.” For example, prairies, small seeps/bogs, pine savannah wetlands, and longleaf pine uplands were all pyrogenic communities maintained during presettlement times at least in part by fire (the fires due to both natural causes and the activities of Native Americans). Under current fire suppression regimes, these fire-adapted communities have been (and are still being) replaced by different suites of plants (Watson 1975; Simberloff 2000b). In fact, fire suppression is one of
164 INTRODUCTION/NATURAL HISTORY OF BIG THICKET the most detrimental changes affecting natural communities in the Big Thicket at the present time. For example, MacRoberts and MacRoberts (2000) summarized numerous studies (e.g., McClung 1988; Bridges & Orzell 1989b) and observations pointing to the critical need for fire in maintaining Wet Pine Savannahs in the Big Thicket National Preserve (e.g., Hickory Creek Unit) and adjacent areas—many areas that were previously savannah have become, only a few decades later, so invaded by shrubs (e.g., Cyrilla racemiflora, Ilex vomitoria) that they can no longer be called savannah. Given the current low incidence of unintentional fire, only active intervention (frequent controlled burns) will result in the maintenance of significant areas of savannah (MacRoberts & MacRoberts 2000). Another example is the Loblolly Unit of the national preserve, which has undergone change from prairie to loblolly pine-hardwood forest in a little over 100 years (Watson 1975). Even now, however, small areas of prairie can still be found in the Big Thicket—Windham Prairie in Polk County is a good example. Brown et al. (2002b) found that this small (2–3 hectares) area is apparently maintained at least in part by special edaphic conditions. Its soil, derived from the Fleming Formation, is a gravelly, thin, well-drained, calcareous clay with a high shrink-swell potential and slow permeability (McEwen et al. 1987; Brown et al. 2002b). DIVERSITY IN THE BIG THICKET—Two things in particular that have been noted during detailed studies of the vegetation of the Big Thicket (e.g., Marks & Harcombe 1975, 1981; Harcombe & Marks 1977) are 1) high beta diversity (= between-habitat diversity, i.e., many species because of many different habitats) and 2) high alpha diversity (= within-habitat diversity, i.e., many species within each habitat—e.g., high richness of woody species particularly in the understory). In general, the coastal plain of the southeastern U.S. is rich in species of vascular plants and is characterized by many community types (Braun 1950; Marks & Harcombe 1975). Marks and Harcombe (1975) suggested that the area of the Big Thicket displays both of these characteristics. HABITAT DIVERSITY—One of the most visually striking features of the Big Thicket is the close proximity of numerous radically different habitats and communities. Some sources have even suggested that the Big Thicket contains more kinds of ecosystems than any other place FIG.91/VIEW OF VILLAGE CREEK IN THE NATURE CONSERVANCY’S ROY E. LARSEN SANDYLAND SANCTUARY,HARDIN CO.(PHOTO BY GMD).
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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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60 INTRODUCTION/SOILS OF BLACKLAND
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66 INTRODUCTION/CLIMATE OF EAST TEX
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Forests define East Texas, and to a
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78 INTRODUCTION/GEOLOGY OF PINEYWOO
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80 INTRODUCTION/PRESETTLEMENT, EARL
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88 INTRODUCTION/PRESETTLEMENT VEGET
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90 INTRODUCTION/CURRENT VEGETATION
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106 INTRODUCTION/POST OAK SAVANNAH
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108 INTRODUCTION/POST OAK SAVANNAH
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110 INTRODUCTION/GEOLOGY AND SOILS
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214 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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