Wednesday, August 8, 2007

PS 40-2: Spatial pattern of Prosopis glandulosa (honey mesquite) and its influence on soil C and N in a subtropical savanna landscape

Feng Liu1, Ben Wu1, E Bai1, Thomas W. Boutton1, and Steven R. Archer2. (1) Texas A&M University, (2) University of Arizona

Encroachment of the leguminous shrub, Prosopis glandulosa (Honey Mesquite) into grasslands of the Rio Grande Plains has occurred over the past century. Understanding of the spatial pattern of mesquite trees and associated patterns of soil carbon and nitrogen pools will help predict the future of these landscapes and evaluate the impacts of this vegetation change on regional C and N cycles. The objective of this study was to quantify the spatial pattern of mesquite trees in contrasting habitats and their influence on soil organic carbon (SOC) and total nitrogen (TN). Locations of mesquite trees ³ 5cm basal diameter were georeferenced within an upland woody grove (~900 m2) and within a 30 m ×50 m plot in a drainage woodland. Samples of associated soils (0-15cm) were collected, georeferenced, and analyzed for SOC and TN. Ripley’s K analysis indicated mesquite trees were randomly distributed in both habitats. SOC and TN had significant negative correlations with distance to mesquite in the grove, but not in the woodland; but their variability decreased with increasing distance to mesquite trees in both habitats.  Results confirm that mesquite trees have strong influence on the amount and the variability of SOC and TN in upland groves. However, in woodlands, this influence is likely obscured by other processes (e.g., flooding that may redistribute litter and surface soil). These findings have implications for understanding spatial variability in plant-soil relationships, for designing sampling protocols to assess and monitor SOC and TN pools, and for parameterizing and testing spatially explicit ecosystem models.

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