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

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ORIGIN AND DIVERSITY OF EAST TEXAS FLORA/INTRODUCTION 201 FIG. 115/ GENERALIZED MAP OF LATE CRETACEOUS VEGETATION FOR NORTH AMERICA SHOWING VEGETATION ZONES.T,TROPICAL FOREST;P, PARATROPICAL FOREST; B,BROAD-LEAVED EVERGREEN FOREST; D,POLAR BROAD-LEAVED DECIDUOUS FOREST (MODIFIED FROM UPCHURCH & WOLFE 1987, WITH PERMISSION OF CAMBRIDGE UNIV.PRESS,©1987). Pangaea known as Laurasia) is considered a single “Holarctic” biogeographic region. Two major dispersal routes into North America existed, one from Europe (the North Atlantic land bridge) and the other from Asia across the Bering Sea area (the Beringian pathway/Bering land bridge). It should be emphasized that average global temperatures were much warmer during portions of the Cretaceous and Tertiary periods (Fig. 11), with ecosystems expanded much beyond their current distributions. Fossil evidence shows that tropical rain forests ultimately extended as far north as 45º to 50º N latitude, paratropical (= near-tropical) rain forests to 60º to 65º (70º in coastal areas), and broad-leaved deciduous forests to polar areas (Wolfe 1975; Upchurch & Wolfe 1987; Wolfe 1987; Wendt 1993; Graham 1999) (see Fig. 115 for map of Late Cretaceous North American vegetation). Specific examples of extended ranges include broad-leaved evergreen paratropical rain forest in Alaska, alligators from Ellsmere Island in northern Canada (then at 79º N latitude), and deciduous trees (e.g., Alnus, Larix, Ginkgo) in the Canadian high Arctic (Graham 1993a, 1999). The striking global high temperatures (“hothouse” conditions) causing these distribution patterns reached their maximum during the Early Eocene Epoch (55 to 50 million years ago) and represent the highest temperatures of the entire Cenozoic Era. They were associated with an increase in volcanic activity worldwide and a concomitant increase in atmospheric CO2 (Graham 1999). Sea levels also varied significantly, with areas now underwater (e.g., Bering Sea between Alaska and Asia) sometimes exposed and providing extensive terrestrial migration corridors. Thus, at times, migration across high northern latitudes was probably relatively uninhibited. Temperate plants are thought to have migrated across both dispersal routes (North Atlantic land bridge, Beringian pathway), and significant numbers of tropical plants also migrated across the North Atlantic land bridge (then at 45º to 50º N latitude) and possibly (in a more limited way) across Beringia.
202 INTRODUCTION/ORIGIN AND DIVERSITY OF EAST TEXAS FLORA The fossil record, reflecting these connections of North America to Europe and Asia, shows that many plant and animal groups had widespread distributions across much of the Northern Hemisphere—temperate forests, for example, occurred very broadly as early as the Late Cretaceous and reached their maximum extension in the Middle to Late Miocene Epoch (the Miocene extended from 23.8–5.3 million years ago (mya)) of the Tertiary Period (Graham 1993a). Particularly during the Tertiary, “there was a belt of vegetation similar in structure and composition extending around much of the northern hemisphere” (Graham 1999). This widespread largely temperate flora has sometimes been referred to as the Arcto- Tertiary geoflora or the Tertiary mesophytic flora (e.g., Graham 1993a). It should be noted that this extensive temperate forest included various gymnosperms (e.g., Ginkgo, Metasequoia, Sequoia) as well as deciduous angiosperms (Davis 1983; Manchester 1999). Other authors, recognizing numerous connections between Old World tropical plant groups and taxa in the New World, have referred to a Tertiary boreotropical flora (Wolfe 1975; Tiffney 1985a, 1985b; Zona 1990; Lavin & Luckow 1993; Wendt 1993; Pipoly & Ricketson 1999, 2000). These workers have emphasized the tropical components of the Tertiary flora and clarified the dispersal of tropical elements from the Old World to the New. Called by whatever name, the resulting widespread Tertiary flora was characterized by both temperate deciduous and tropical components and developed into a “Mixed Mesophytic forest” that “was once more or less continuously distributed throughout the Northern Hemisphere” (Xiang et al. 1998). According to Graham (1999), “With reference to the modern deciduous forest formation [of eastern North America], it is now clear that this community is a complex mixture of elements derived from various sources. Some certainly came from mesic Cretaceous ancestors and evolved in the high northern latitudes. Others are clearly derived from tropical groups that have evolved temperate components (e.g., Diospyros virginiana, the persimmon, a New World temperate representative of the primarily tropical family Ebenaceae). The contribution of Old World tropical elements to the composition of New World temperate deciduous and tropical forests is only now becoming fully recognized and constitutes support for the concept of a boreotropical flora.” It is thus now clear that the present eastern deciduous forests, including those of East Texas, have a complex origin including both temperate and tropical elements from the Old World that arrived during the Cretaceous and Tertiary periods. Other species have evolved in place in eastern North America and still others represent more recent arrivals. There also have been extensive geohistorical changes from the mid-Tertiary Period to the present that have had a profound impact on the development of the plant communities we see today. These include alterations in the shapes of the northern land masses (e.g., separation of North America and Eurasia due to tectonic plate movement), fluctuations in sea levels, mountain building, and profound changes in the climate (e.g., major change in average global temperature, glaciation). As a result of these events, there have been great changes in both the composition and the disposition of the flora. In particular, many once widespread plant groups have experienced restrictions in their ranges, resulting in a number of interesting disjunct distribution patterns. Cooling in the Late Tertiary (Late Miocene to Pliocene) and the approximately 20 glacialinterglacial cycles of the Pleistocene Epoch (“ice ages”) were particularly important in determining the survival of species in various parts of the northern hemisphere. During the Late Tertiary and Quaternary (including the Pleistocene) in eastern North America, the “diverse physiography and the north-south orientation of the American mountains allowed the deciduous forest to persist in local refugia and to migrate in response to changes in climate” (Graham 1999). In other words, as glaciers moved down from the north, there was no eastwest mountain barrier to prevent the southern migration of plants. Graham (1999) stressed that the north-south alignment of the mountains and the “continuous land connections to boreal zones to the north and tropical zones to the south made the region both a pathway and a refugium for plants and animals.” Likewise, in eastern Asia, conditions were conducive to the persistence of the once widespread Tertiary forest elements—in fact, more have sur-
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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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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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