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

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FIG. 123/MAP SHOWING EXTENT OF ICE AT END OF THE LAST GLACIAL MAX- IMUM (18,000 YEARS BEFORE PRESENT) WITH LOCATION OF VEGETATION TYPES AT THAT TIME. T—TUNDRA; BF—BOREAL FOREST; MF—MIXED FOREST (CONIFER-NORTHERN HARDWOOD); DF—DECIDUOUS FOREST; SE—SOUTH- EASTERN EVERGREEN FOREST; SS—SAND DUNE SCRUB.(MODIFIED FROM DAVIS 1983 AND DELCOURT & DELCOURT 1993). oaks with some open grassland areas. Bryant and Holloway (1985b) further suggested that around 1,500 years before present, the modern day oak-savannah vegetation (Post Oak Savannah) became established, reflecting “a prolonged period of drier, and perhaps warmer, climatic conditions.” However, Bousman (1998) has more recently concluded that arboreal cover reached its low point in the area about 5,000 years ago and has increased since that time. Given the difficulty of determining with confidence the changes in paleoclimates, he emphasized that there probably have been “numerous shifts between forest, woodland, and open plant communities” in the area since the end of the last glaciation (approximately 18,000–15,000 years ago). The vegetation pattern present at the time of settlement, while often mistakenly viewed as static, was in a state of flux, and was thus just one point in a continuing series of changing conditions (Smeins 1984). It is interesting to consider the effects of past glaciation on the present flora. Many otherwise difficult to explain modern plant distributions may be easily accounted for by regarding them as the result of changing climatic conditions of the past. One example is the occurrence of Cladium mariscoides (smooth saw-grass, Cyperaceae) disjunct to a few bog localities in East Texas and the far southeastern U.S., but otherwise known only from southeastern Canada and the northeastern U.S. as far south as South Carolina and Tennessee (Bridges & Orzell 1989a; Tucker 2002c). Another possible example is the occurrence of jack-in-the-pulpit (Arisaema triphyllum) in Parker County in the West Cross Timbers. This species is generally limited to mesic environments in the eastern part of the state. Nonetheless, a thriving population can be found in a mesic “rockhouse” microhabitat between sandstone rock walls in Parker County, well to the west of other known locations of this species (Diggs & O’Kennon 2003). It seems likely that this population is a relict from a previously extensive forest that was largely lost as the climate warmed and dried. Such persistence in climatically moderated “rockhouse” environments has been documented for a variety of plant species, including endemics, in the eastern U.S. (e.g., Walck et al. 1996; Farrar 1998). Other eastern species that have been found surprisingly far west in Texas include eastern hop-hornbeam (Ostrya virginiana) in Tarrant County and shag-bark hickory (Carya ovata) in Parker County, both separated by more than 120 miles (193 kilometers) from their present distributions in East Texas. Numerous other examples could be given, including many species and genera ORIGIN AND DIVERSITY OF EAST TEXAS FLORA/INTRODUCTION 209 FIG. 124/ MODERN DISTRIBUTION OF PICEA GLAUCA (PINACEAE) (WHITE SPRUCE) (FROM TAYLOR 1993, WITH PERMISSION OF OXFORD UNIV.PRESS).
210 INTRODUCTION/ORIGIN AND DIVERSITY OF EAST TEXAS FLORA typical of East Texas which show up in isolated pockets on the Edwards Plateau (e.g., groundnut (Apios americana), crossvine (Bignonia capreolata), witch-hazel (Hamamelis virginiana) (Fig. 125), spicebush (Lindera benzoin), barbed rattlesnake-root (Prenanthes barbata), Carolina rose (Rosa carolina), dwarf palmetto (Sabal minor), and American basswood (Tilia americana)). Likewise, many other typically eastern species extend west in the Red River valley (e.g., numerous species reach their western limits in Grayson County, including beaked groovebur (Agrimonia rostellata), black oak (Quercus velutina), may-apple (Podophyllum peltatum), and great Solomon’s- FIG. 125/TEXAS DISTRIBUTION OF WITCH-HAZEL (HAMAMELIS VIRGINIANA), seal (Polygonatum biflorum)). In addition, many AN EXAMPLE OF THE NUMEROUS SPECIES THAT OCCUR IN TEXAS PRIMARILY herbaceous species common farther north IN EAST TEXAS, BUT WITH ISOLATED OCCURRENCES ON THE EDWARDS and east in the U.S. occur in Texas only rarely PLATEAU (FROM TURNER ET AL.2003, WITH PERMISSION OF BILLIE TURNER and erratically in the Pineywoods and have AND THE BOTANICAL RESEARCH INSTITUTE OF TEXAS). extremely limited distributions. Kral (1966c) and MacRoberts and MacRoberts (1997a) discussed a number of these “northern woodland elements” south of their normal range (e.g., Erythronium rostratum (yellow trout-lily), Lilium michauxii (Carolina lily), Sanguinaria canadensis (bloodroot), Silene stellata (widow’s-frill), Trillium recurvatum (prairie trillium), Uvularia sessilifolia (sessile-leaf bellwort)), and indicated that they appear to be relicts of glacial times surviving in areas with particularly favorable soil and moisture conditions (i.e., refugia). Kral (1966c) noted that he could walk for miles and then find a large colony of one of these species, apparently reproducing predominantly via vegetative means. These species may thus be “Ice Age holdovers hanging on precariously to the older geologic terraces in the coolest locations in the forest” (MacRoberts & MacRoberts 1997a). Even the presence of the drought-intolerant American beech (Fagus grandifolia) in East Texas is surprising, given its ecological requirements. This species reaches its southwestern limit in the U.S. in Montgomery County (not far north of Houston)—here beech appears to do best when protected from the intense Texas summer sun by a canopy of associated trees (McLeod 1975). Perhaps most surprisingly, a single plant of yellow lady’s-slipper orchid (Cypripedium parviflorum var. pubescens) was found somehow surviving near Muleshoe in Bailey County in the Texas Panhandle—it was possibly a relict of a widespread northern coniferous forest that at one time extended to the south during a colder and wetter period of the Pleistocene Epoch (Liggio & Liggio 1999). All of these examples may be relicts of populations much more widespread during glacial times when the climate in Texas was quite different and conditions much more mesic (Palmer 1920; Kral 1966c; O’Kennon 1991; Delcourt & Delcourt 1993). It is not surprising that isolated populations are able to persist in small areas of special microclimate or unusual geology—in fact, such persistence would be expected. Thus, the flora of East Texas is in part a unique reflection of glacial times—when northern species like Fagus grandifolia (American beech) and Carya alba (mockernut hickory) were brought together with southern plants like Magnolia grandiflora (southern magnolia) and Sabal minor (dwarf palmetto) (Fritz 1993). In addition to individual species, several unique habitats occur in East Texas which reflect the different climatic conditions of the past. The “Lost Pines” of Bastrop County, an area of about 181 square km (70 square miles) of pine-oak woodland isolated west of the main body of East Texas pines by approximately 162 km (100 miles) (Texas Parks and Wildlife 2002b), is probably the remnant of a more extensive Ice Age forest (Maxwell 1970).
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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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260 INTRODUCTION/BOTANICAL ART IN E
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