Shrub species richness beneath honey mesquite on root-plowed rangeland.

Abstract

Root-plowed rangeland in southern Texas is often dominated by fabaceous shrubs. We tested the hypothesis that the shrub community present 40 years after rootplowing does not exhibit successional trends toward the mixed-brush species community that existed before rootplowing. Twenty shrub clusters, each organized around a central honey mesquite individual, were selected within a control site and a root-plowed (35-40 years ago) site at each of 3 locations. Number of all woody plants species including cacti Opuntia spp. and Yucca spp. beneath the nuclear honey mesquite was determined. Shrub species richness within clusters increased with increasing central honey mesquite basal diameter on control and root-plowed sites. Species richness/honey mesquite in root-plowed (2 +/- 0.5 species, +/- SE) sites was lower than species richness/honey mesquite > 200 mm in diameter on control sites (7 +/- 0.4 species/honey mesquite). Honey mesquite seedlings (1-60 mm basal stem diameter) composed 39 +/- 14% of the shrubs beneath honey mesquite canopies on root-plowed sites compared to less than or equal to 3% of the woody plants present on untreated sites. Honey mesquite may continue to dominate root-plowed sites for some time, since honey mesquite was the major subordinate shrub species on root-plowed sites.