Document: DAV-3-69-43

The effects of livestock grazing and climate variation on vegetation and grasshoppers in the northern Chihuahuan Desert.

LIGHTFOOT, D.C.* ¹ and L.F.HUENNEKE ²

The University of New Mexico, Albuquerque, NM 87131 USA ¹
New Mexico State University, Las Cruces, NM 88003 USA ²

Abstract:
Domestic livestock grazing on semi-arid rangelands of the American Southwest represents an ecological perturbation with a long history of changes in biotic communities. Reduction of native perennial grasses and increases in weedy annual herb and perennial shrub plant species are well documented on historically grazed semi-arid Western rangelands. Variation in climate has also produced considerable impacts on Southwestern ecosystems, such as the 1950's drought, and a recent trend toward a wetter and warmer climate. The interactive effects of livestock grazing and climate fluctuation on biotic communities are not well understood. Grasshoppers are important native herbivores on western rangelands, and climate is known to be a key factor controlling their populations. We measured vegetation and grasshoppers for five years at a series of five semi-arid sites in New Mexico, to assess the interactive effects of livestock grazing and short-term climate variation on plant and grasshopper community structure and population dynamics. Our five study sites ranged from shrub to grass dominated. The five-year study period included both wet El Nino and dry La Nina climatic events. Our results demonstrate that livestock grazing 1) Alters plant and grasshopper species composition and population dynamics, 2) favors weedy species, and 3) affects both grass and shrub dominated communities in similar ways. Variation in precipitation patterns increased the amplitude of ecological grazing impacts favoring weedy species in wet years on grazed lands. Annual plants and ground-dwelling grasshoppers were significantly more abundant on grazed land, and correlated with precipitation over time. Perennial grasses and grass-dwelling grasshoppers were significantly greater on non-grazed land, and correlated less to variation in rainfall over time. These findings indicate that domestic livestock grazing reduces the stability of semi-arid ecosystems.

Keywords: livestock grazing, disturbance, vegetation, grasshoppers, climate

This abstract is being presented at: 3:45 PM in session:
Oral Session #51: Disturbance Ecology: Harvesting, Grazing and Roads.