Vegetation response of a mesquite-mixed brush community to aeration

Abstract

Responses of plant communities to mechanical treatments such as aeration on semiarid rangelands are not clearly understood. Our objective was to compare woody and herbaceous plant cover, density, and diversity on aerated and nontreated rangelands. Five rangeland sites that were aerated with a double/tandem drum aerator during summer 1998 and 5 sites of nontreated rangeland were selected for study on the Chaparral Wildlife Management Area, La Salle County, Tex. Woody plant cover was estimated using the line-intercept method, and stem density was estimated in 30 × 1.5 m plots in 1999 and 2000. Forb and grass cover and density were estimated in 20 × 50 cm quadrats during spring and fall 1999. Woody and herbaceous plant diversity did not differ between treatments. On aerated sites percent woody plant cover was 4-fold less 1-year after aeration and increased 89% from the first to the second growing-season post treatment. Canopy cover of honey mesquite (Prosopis glandulosa Torr.), twisted acacia (Acacia schaffneri S. Wats.), and Texas pricklypear (Opuntia lindheimeri Engelm.) was greater on non-treated sites. By the second growing season after aeration, density of honey mesquite was greater on aerated sites, whereas Texas pricklypear had declined on aerated sites. Density of spiny hackberry (Celtis pallida Torr.) and Texas persimmon (Diospyros texana Scheele) was greater on aerated sites during the first growing-season post treatment. Cover and stem density of hog-plum (Colubrina texana T. G.), coma (Bumelia celastrina Kunth), and whitebrush [Aloysia gratissima (Gill. Hook.) Tron.] did not differ among aerated and nontreated sites by the first growing season after aeration. Forb cover was greater on aerated sites in spring 1999. Fringed signalgrass [Brachiaria ciliatissima (Buckl.) Chase], fall witchgrass [Digitaria cognata (Schult.) Pilger], and bristlegrass (Setaria spp. Beauv.) cover was greater on aerated sites in spring and fall 1999, whereas purple threeawn (Aristida purpurea Nutt.) was greater on nontreated sites. It is unclear to what degree environmental factors such as pre- and post-treatment climatic conditions and herbivory may have influenced vegetation response to aeration. The rapid regrowth of many woody plants following aeration may require the application of maintenance treatments within a relatively short time period to maintain treatment benefits. Aeration reduced total woody plant cover, increased the density of desirable woody plants, maintained woody plant diversity, increased grass cover, and may be a useful tool in managing South Texas rangelands for white-tailed deer (Odocoileus virginianus Boddaert) and cattle.