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

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SOILS OF BLACKLAND PRAIRIE/INTRODUCTION 63 The smectitic clays also result in both slickensides and gilgai, two phenomena often seen in Vertisols. Slickensides are planes of weakness in the soil caused by movements associated with shrinkage and swelling. These can lead to rather large-scale slippage or failure of soil blocks, which can be problematic in construction (Hallmark 1993). According to Hallmark (1993), the collapse of the walls of construction trenches, caused by slickenside slippage, results in Texas workers being crushed to death in trenches almost every year. Gilgai are the microhigh, microlow topography or relief features found on essentially all Vertisols (Diamond & Smeins 1993). On flat areas in the prairie landscape, gilgai typically form circular, almost tub-like depressions, called “hog wallows” by early settlers. These range from about three to six meters across and up to about one-half meter deep (Hayward & Yelderman 1991). On slopes, gilgai take the form of microridges and trough-like microvalleys up to about 20 centimeters deep which run perpendicular to the contour of the slope (Miller & Smeins 1988; Diamond & Smeins 1993) (Fig. 31). Both gilgai and the great soil depth of this region are the result of the constant churning and overturning of the shrink-swell, clay-based soils. When these soils shrink during dry weather and large cracks form, loose pieces of soil fall deep into the cracks. Upon wetting, these pieces swell and exert lateral pressure on adjacent soil particles. Soil below is pushed outward and eventually upward, resulting in depressions rimmed by slightly raised areas (Hayward & Yelderman 1991) (Fig. 32). Gilgai are thus formed and the soil is slowly but continually churned in a cycle of overturning or self-plowing (Steila 1993), a type of pedoturbation (soil-mixing). On the native Blackland Prairie, soil erosion was low because of the dense tall grass community and also because of the water-trapping capacity of gilgai. Temporary water storage in the numerous gilgai depressions has been estimated at one-half acre-foot of water per acre of flat prairie. As much as six inches of rain could be temporarily trapped in these structures before runoff began (Hayward & Yelderman 1991). This would have greatly reduced runoff and allowed significant infiltration, particularly important considering that clay soils are often rather impermeable. In fact, early accounts refer to clear runoff and clear streams on the Blacklands (Hayward & Yelderman 1991), in stark contrast to present-day conditions. For example, McClintock (1930) in 1846 described the San Gabriel in the Blackland Prairie north of Austin as “so transparent are its waters that fish, and even small pebles [sic] can be disserned [sic] at a depth of ten feet.” However, because thousands of gilgai covered the prairies and created pools of standing water during wet weather, the prairies were at times virtually impassable for early settlers (Hayward & Yelderman 1991). Under present agricultural conditions, with no plant cover during much of the year and with the suppression of gilgai formation by plowing, erosion rates in the Blacklands are high. Thompson (1993) noted that the Blacklands have one of the highest rates of soil loss on cropland of any major area in Texas—from tens to hundreds of times higher than under the original native prairie vegetation (Hayward & Yelderman 1991). Richardson (1993) cited annual erosion figures of 15 tons per acre (t/a) for a cultivated Blackland area, compared with only 0.2 t/a for a native grass meadow, a 70-fold difference. Such a loss is clearly not sustainable indefinitely and it raises important questions about current agricultural practices. Even though gilgai were one of the most evident surface features on the original Blackland Prairie, because they are destroyed by plowing, they are rarely observed today. Excellent examples of these “hog wallows,” however, can still be seen at the Nature Conservancy’s Clymer Meadow preserve in Hunt County, the Matthews-Cartwright-Roberts Prairie in Kaufman County, and Austin College’s Garnett Prairie in Grayson County, as well as on other scattered prairie remnants (Fig. 33). It should be noted that due to the continuing soil movement associated with Vertisols, gilgai can reform if soils are left undisturbed for decades. Mollisols are found on the Blackland Prairie on rocks of the Austin Group. These areas have high calcium carbonate levels and consolidated parent rocks. Because bedrock is usually just below the surface, root growth and soil water storage are restricted. Typically, Mollisols
64 INTRODUCTION/SOILS OF BLACKLAND PRAIRIE FIG.33/PHOTOGRAPH OF GILGAI ON SLOPE (SHOWING MICROVALLEY AND MICRORIDGE EFFECT) ON VERTISOL IN NORTHERN GRAYSON CO.,TX (PHOTO BY GMD). FIG.34/PHOTOGRAPH OF MIMA MOUND ON ALFISOL IN NORTHERN GRAYSON CO., TX (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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Page 31 and 32: 14 INTRODUCTION/GUIDE TO ARRANGEMEN
Page 33 and 34: 16 INTRODUCTION/GUIDE TO SOURCES OF
Page 35 and 36: 18 INTRODUCTION/GUIDE TO GEOGRAPHIC
Page 37 and 38: 20 INTRODUCTION/GUIDE TO ENDANGERED
Page 39 and 40: 22 INTRODUCTION/GUIDE TO GLOSSARY,
Page 41 and 42: 24 INTRODUCTION/GUIDE TO ABBREVIATI
Page 43 and 44: 26 INTRODUCTION/SUMMARY DATA ON FLO
Page 45 and 46: 28 INTRODUCTION/ACKNOWLEDGMENTS Kar
Page 47 and 48: 30 INTRODUCTION/AUTHORS’ NOTE Pre
Page 49 and 50: 32 INTRODUCTION/GENERAL GEOLOGY OF
Page 63 and 64: 46 INTRODUCTION/SOILS SOIL ORDER DE
Page 65 and 66: 48 INTRODUCTION/SOILS, EAST TEXAS B
Page 67 and 68: 50 INTRODUCTION/SOIL-RELATED GEOLOG
Page 77 and 78: 60 INTRODUCTION/SOILS OF BLACKLAND
Page 79: 62 INTRODUCTION/SOILS OF BLACKLAND
Page 83 and 84: 66 INTRODUCTION/CLIMATE OF EAST TEX
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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
Page 125 and 126: 108 INTRODUCTION/POST OAK SAVANNAH
Page 127 and 128: 110 INTRODUCTION/GEOLOGY AND SOILS
Page 129 and 130: 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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126 INTRODUCTION/POST OAK SAVANNAH
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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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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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