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There has been recent concern regarding the effects of range management practices on biodiversity. Our objective was to determine the long-term (~30 years) effects of chaining, and chaining followed by root plowing, on vegetation diversity in an ephemeral drainage system. Plant species richness and diversity were estimated in 2 chained (ca. 1950) areas, 2 chained (ca. 1950) and root-plowed (ca. 1960) areas, and 2 untreated areas during April 1993. Beta diversity within treatments was estimated with mean dissimilarity (l-mean similarity). Mean similarity was quantified with Jaccard's index. Spatial gradient analysis in which pairwise similarities were regressed against the distance between each pair of samples within a site was used to describe similarity within a site. Species richness and diversity were similar among treatments for both herbaceous and woody species. Similarity (Jaccard's index) among transects within a site increased with increasing degree of disturbance. Chained and root plowed sites had lower beta diversity than chained or untreated sites. Similarity in the chained and root plowed sites varied randomly, not spatially, while the control (untreated) and chained sites had negative spatial gradients, indicating spatial heterogeneity within these sites. Although root plowing did not reduce species richness and diversity as reported on upland sites in previous studies, beta diversity and habitat heterogeneity were lower on chained and root plowed sites than on chained or untreated sites.

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The effects of herbicide applications to kill honey mesquite (Prosopis ghdulosa Torr.) on community diversity are poorly documented. Our objective was to test the hypothesis that herbicide application to kill honey mesquite would reduce plant and vertebrate species richness and diversity. A 1:l mixture of triclopyr ([(3,!!,6-trichloro-2-pyridinyl) oxylacetic acid] + picloram (4-amino-3,5,6tricholopicolinic acid) was applied to three 13-ha plots during 1992 and to 3 additional plots in 1993. Mesquite and forb canopy cover in the zone I 1 m from the soil surface were lower within treated plots than in control plots (n = 3) following the 1992 and 1993 treatments. Grass canopy cover did not differ between herbicide-treated plots and control plots. Vegetation species richness and evenness, Shannon's index, beta diversity, and proportion of rare plant species did not differ between controls and sites treated during 1992 and 1993. Rodent and avian relative frequency, richness, and diversity were not different on 1992 herbicide treatment plots and controls. Based on these results, application of triclopyr + picloram in mesquite-mixed grass communities in the Texas Coastal Bend does not appear to reduce plant and vertebrate species richness and diversity within the first 2 years after treatment. However, our results should be interpreted cautiously because (1) annual rainfall was 16 % above the annual average during the study and (2) limited replication possibly reduced statistical power to detect differences.