Document: KIR-3-40-11

Vegetation dynamics of an oak-juniper savanna on the Edwards Plateau of Texas: An isotopic assessment.

JESSUP, K.E.* ¹, K.D.BARKER ¹, P.W.BARNES ¹ and T.W.BOUTTON ²

Southwest Texas State University, San Marcos, TX 77843-2126 USA ¹
Texas A&M University, College Station, TX 77843-2126 USA ²

Abstract:
The vegetation of the Edwards Plateau of central Texas prior to European settlement (i.e., 100-200 years ago) is not well characterized. Anecdotal accounts suggest grasslands and plateau live oak savannas (Quercus virginiana var. fusiformis) may have covered much of the region, and that factors such as fire suppression and domestic grazing may have caused a recent increase in the abundance of herbaceous and woody C3 plants, such as the woody ashe juniper (Juniperus ashei). We used ¹³C values from soil organic matter and vegetation to quantify shifts in C3/C4 plant composition during the last several hundred years at an upland savanna parkland on the eastern Edwards Plateau. ¹³C values of grassland soils increased with depth, from ca. -21 to -14 (surface vegetation to 30 cm depth, respectively). Carbon isotope values of soils beneath large, solitary live oaks also increased with depth, from ca. -27 to -19 (surface litter to 30 cm depth, respectively), though they showed a stronger C3 signature than grassland soils at all depth intervals. These results suggest that the C3 component of sites currently dominated by grassland or discrete live oaks, has increased significantly in the recent past.

Keywords: savanna; grassland; isotope; delta¹³C; soil organic matter; C3 plant; C4 plant; Edwards Plateau; ashe juniper; live oak; woody plant.

This abstract is being presented at: 3:30 PM in session:
Poster Session #17: Vegetative Analysis.