Plant, small mammal, and avian diversity following control of honey mesquite

Abstract

The effects of herbicide applications to kill honey mesquite (Prosopis glandulosa 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 1:1 mixture of triclopyr ([(3,5,6-trichloro-2-pyridinyl) oxy]acetic acid) + picloram (4-amino-3,5,6-tricholopicolinic 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 less than or equal to 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.