Bandelier National Monument erected a series of ungulate exclosures and paired reference areas to evaluate elk (Cervus elaphus nelsoni) impacts on the vegetative community in pinyon (Pinus edulis)-juniper (Juniperus spp.), ponderosa (Pinus ponderosa) grassland, and mixed-conifer habitat types. Plant densities were higher in ponderosa grassland habitat than those clipped twice or not at all. Litter cover in ponderosa grassland habitat was negatively correlated with clipping frequency in the absence of trampling, although increased trampling confounded effects. Measures of basal area did not change with this first year's treatment. Species richness was affected in mixed-conifer sites where a combination of the extreme frequencies of clipping or trampling coupled with moderate levels of the other treatment resulted in fewer species. Clipping x trampling frequencies had a significant effect on litter cover in ponderosa grassland habitat and species richness in mixed-conifer sites. Recurrent impacts from elk grazing and concomitant trampling may accelerate the rate at which plant communities reach thresholds of vulnerability.
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