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Summer fire impacts and isotopic assessment of vegetation dynamics in Texas coastal Quercus virginiana communities
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Woody plants have increased in abundance in many grasslands and savannas worldwide. Anecdotal evidence suggests that Quercus virginiana (live oak) has increased in the Gulf Coastal Prairies of Texas since European man introduced livestock and altered fire frequencies  200 years ago. The purpose of this study was to: (1) reconstruct plant community history in coastal Q. virginiana plant communities based on the natural abundance of isotopes in plants and soils, and (2) evaluate the potential of summer fires to reduce Q. virginiana in grasslands. Woody plant stem density, height, cover, and species composition were quantified following summer fires in 1996 and 1998 at Aransas National Wildlife Refuge. After two slimmer fires, stem densities of woody plants were reduced by 36% and 90% in the 0-5 mm and 6-49 mm stem diameter classes, respectively. Reductions in woody canopy cover promoted greater herbaceous cover in the burned thickets. There were no significant effects on woody plant species composition. Previous cool season bums controlled stem height, but perpetuated thickets by promoting sprouting. Repeated summer fires may have the potential to break this cycle and reduce woody plant abundance. ¹³C of plants and soils at Kansas indicated that grasslands, Quercus virginiana mattes, and Q. virginians thickets have been landscape components for at least the past several decades. In grasslands, C₄ grasses have become relatively more productive where long-term livestock grazing has recently ceased. Some soil organic C below 20 cm in mottes was from C₄ grasses, suggesting mottes once supported a C₄ understory,¹³C of organic C in buried A-horizons (¹³C = -16.8) at Aransas indicated that C₄ grasslands once dominated the study area, perhaps 100 to 200 years ago. At Kenedy Memorial Foundation Ranch, ¹³C values of soil organic C were in approximate equilibrium with those of the vegetation, suggesting plant communities have changed little over the past several decades. The presence of C₄ grass C in thickets suggest some thickets may be recent at Kenedy. ¹⁵N of plants and soils did not enhance interpretation of vegetation dynamics at either site, but may provide insights regarding the N-cycle of these oak communities.
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Includes bibliographical references (leaves 93-100).
Issued also on microfiche from Lange Micrographics.
Hays, Kelley Ann (1999). Summer fire impacts and isotopic assessment of vegetation dynamics in Texas coastal Quercus virginiana communities. Master's thesis, Texas A&M University. Available electronically from
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