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

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■ POSITION ON THE ECOTONE or transition zone between the eastern deciduous forests and the central North American grasslands (ecotones frequently contain high levels of diversity—Risser 1995). A quantitative analysis of the east-west floristic transition across Texas (MacRoberts & MacRoberts 2003b) demonstrated that this change occurs in an approximately 300 km wide band (see Fig. 130) extending from around 95° to 99° west longitude (roughly from Houston and Tyler on the east to Wichita Falls and San Antonio on the west),with much of this area being within the boundaries of East Texas (depending on the latitude, East Texas as defined here extends from just east of 94° to just west of 98° longitude). Austin, at the western margin of East Texas, is one of the areas where the east and west influences are approximately balanced. While Texas has long been recognized as a transition zone, (e.g., Blair 1950; Gehlbach 1991; Diggs et al. 1999), the MacRoberts and MacRoberts study is the first to quantitatively document the area of most rapid change. ■ PROXIMITY TO OTHER SOURCE FLORAS—The intermingling of elements typical of the eastern deciduous forest, southeastern swamps, central North American grasslands, southwestern deserts, and even the tropics is striking and contributes greatly to the overall biological diversity of the area.The tropical and southwestern desert components of the East Texas flora are probably the least obvious. Sorrie and Weakley (2001) discussed these elements in relationship to the diversity of the Atlantic and Gulf Coastal Plain Floristic Province, and plants of these origins are particularly evident in the flora of East Texas. A few examples of the many genera with tropical affinities include Asimina, Eriocaulon, Hymenocallis, Sabal, Tillandsia, and Zephyranthes. In contrast, Abronia, Coryphantha, Lesquerella, Manfreda, Mentzelia, Nolina, and Opuntia are a few of the genera which have affinities with the Sonoran Floristic Province to the west and southwest. ■ RICH BIOGEOGRAPHIC HISTORY—e.g.,remnant Tertiary components (see page 202);remnant northern species as the result of glaciation—e.g., American beech (see page 210). Perhaps the most important of these factors are the area’s position on the ecotone between the eastern deciduous forests and the central North American grasslands and its proximity to the southeastern swamps, the desert southwest, and the nearly tropical area of south Texas. The result is that the East Texas flora is a complex and diverse mixture derived from several major, and quite different, floristic FIG. 131/ THE BIG THICKET AND EAST TEXAS AS A WHOLE AS A “BIOLOGICAL CROSSROADS” (MODIFIED FROM NATIONAL PARK SERVICE 1997). ORIGIN AND DIVERSITY OF EAST TEXAS FLORA/INTRODUCTION 227 provinces (Thorne 1993d). Because of the disparate floristic elements and its mid-continental position, one part of East Texas, the Big Thicket, has been referred to by some as the “Biological Crossroads of North America” (e.g., Gunter 1993). Given the location of the transition zone (MacRoberts & MacRoberts 2003b), the description is even more fitting for East Texas as a whole (Fig. 131). When all information is considered, the East Texas flora is seen to be a unique assemblage of many different elements all coming together and coexisting in a relatively small area— creating an extremely rich flora. B
228 INTRODUCTION/CONSERVATION IN EASTTEXAS CONSERVATION IN EAST TEXAS During the past 200 years, human activities, particularly logging, conversion of habitats for agriculture, flooding of river bottoms for reservoirs, urbanization, and other types of development, have profoundly altered the ecosystems of East Texas. Only tiny remnants of the original habitats have survived to the present day in anything resembling their presettlement state. This is particularly tragic, because in many ways, East Texas is a botanically unique region (Diggs 2002; also Appendix 10) and an area of high biological diversity. As a result of these changes, there are now numerous species that are of conservation concern (Appendix 12). Different organizations and agencies have tracked endangered, threatened, or rare species in the state over the years. Examples include the Texas Organization for Endangered Species (TOES 1993), the Nature Conservancy of Texas (Carr 2001, 2002d), and the Texas Parks and Wildlife Department (Poole et al. 2002). Several categories (sometimes overlapping) of such plants are of particular interest. Of greatest conservation concern are those plants that have an official designation such as “federally endangered” (see page 20 and Appendix 12). While these are limited in number, they generate great publicity and are potentially significant economically. Another large group of species is endemic to Texas (see page 215 and Appendix 11), and many of these are likewise vulnerable. Such plants are of major conservation concern because they are known from nowhere else in the world—they are unique aspects of Texas’ natural heritage. Finally, hundreds of species of plants reach the southwestern limits of their ranges in East Texas and are rare or of very limited occurrence in the state. Many of these species are probably Ice Age relicts, surviving only in a few areas of favorable microclimate or geology (Kral 1966c; MacRoberts & MacRoberts 1997a). Such species are particularly vulnerable to habitat change and could easily be eliminated from the state by the type of widespread habitat transformation now occurring throughout most of East Texas. Like individual species, a number of entire ecosystems/communities are currently of significant conservation concern. The Blackland Prairie (and its constituent communities), for example, originally covered a huge area but has been reduced to a few tiny remnants, more of which are lost each year. Communities on the Carrizo Sands, some of which are unique to Texas, are also under pressure, and what remains are often significantly degraded by grazing, fire exclusion, or other pressures (M. MacRoberts, pers. comm.). Further, a number of communities reach their western limit in Texas and are now vulnerable. Examples include wetland pine savannah (limited in Texas to Hardin, Jasper, Newton, and Tyler counties— MacRoberts & MacRoberts 1998d), hanging bogs (also known as hillside bogs or Wet Herbaceous Seeps), muck bogs, beech-magnolia forest, beech-hardwood forest, etc. These communities face various threats ranging from conversion to pine monoculture, fire suppression, drainage, overgrazing, cultivation, or invasion by exotics to total destruction by development. Each community faces a unique set of problems and, like individual species, these communities need protection, and in some cases active management, if they are to survive into the future. Among the most noteworthy large-scale conservation efforts in East Texas have been the creation of the National Forests, attempts to save part of the Big Thicket (see section on Conservation in the Big Thicket on page 190), the struggle to set aside wilderness areas in the National Forests, efforts to establish and expand a number of National Wildlife Refuges, and the successful creation of an extensive Texas State Park system. The results have included the establishment of the Big Thicket National Preserve, four National Forests (Figs. 89, 132), four major National Wildlife Refuges (including Caddo Lake created in 2000), and dozens of state parks and wildlife management areas (discussed further below). Another major event was the passage of the 1984 East Texas Wilderness Act, which resulted in five officially designated
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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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110 INTRODUCTION/GEOLOGY AND SOILS
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112 INTRODUCTION/SOILS, FIRE, AND T
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114 INTRODUCTION/SOILS, FIRE, AND T
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116 INTRODUCTION/ PRESETTLEMENT, EA
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118 INTRODUCTION/VEGETATION OF POST
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124 INTRODUCTION/CONDITIONS TODAY O
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128 INTRODUCTION/RED RIVER AREA are
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130 INTRODUCTION/BLACKLAND PRAIRIE
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132 INTRODUCTION/GEOLOGY OF BLACKLA
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134 INTRODUCTION/PRESETTLEMENT AND
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144 INTRODUCTION/VEGETATION OF BLAC
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146 INTRODUCTION/FUTURE OF BLACKLAN
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148 INTRODUCTION/FUTURE OF BLACKLAN
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150 INTRODUCTION/CADDO LAKE LOCATIO
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152 INTRODUCTION/CADDO LAKE FIG.84/
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154 INTRODUCTION/PRESENT AND FUTURE
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156 INTRODUCTION/BIG THICKET THE BI
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158 INTRODUCTION/BIG THICKET GEOGRA
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160 INTRODUCTION/NATURAL HISTORY OF
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172 INTRODUCTION/SUMMARY DEFINITION
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