EFFECTS OF SIMULATED ELK GRAZING AND TRAMPLING (II): FREQUENCY

The increase in western North American elk (Cervus elaphus nelsoni) populations is a concern to resource managers. In summer 1998, Bandelier National Monument erected a series of ungulate exclosures and paired reference areas to evaluate elk impacts on the vegetative community in piñon-juniper (Pinus edulis - Juniperus spp.), ponderosa (Pinus ponderosa) grassland (PG), and mixed-conifer (MC) habitat types. We assessed changes in density, percent foliar/litter cover, basal area, species richness, and composition resulting from the application of different frequencies of simulated grazing and trampling within elk exclosures from January through May of 1999 and 2000. Frequent clipping resulted in increased grass densities in PG sites and decreased total standing crops in MC sites after only 1 year. There were clipping X trampling interaction effects. Recurrent impacts from elk grazing and concomitant trampling may accelerate the rate at which plant communities reach thresholds of vulnerability. More years of treatments may detect further vegetative responses to different grazing pressure in this ecosystems, which has a history of elk grazing pressure