Contrasting effects of different mammalian herbivores on sagebrush plant communities

PLoS One. 2015 Feb 11;10(2):e0118016. doi: 10.1371/journal.pone.0118016. eCollection 2015.

Abstract

Herbivory by both grazing and browsing ungulates shapes the structure and functioning of terrestrial ecosystems worldwide, and both types of herbivory have been implicated in major ecosystem state changes. Despite the ecological consequences of differences in diets and feeding habits among herbivores, studies that experimentally distinguish effects of grazing from spatially co-occurring, but temporally segregated browsing are extremely rare. Here we use a set of long-term exclosures in northern Utah, USA, to determine how domestic grazers vs. wild ungulate herbivores (including browsers and mixed feeders) affect sagebrush-dominated plant communities that historically covered ~62 million ha in North America. We sampled plant community properties and found that after 22 years grazing and browsing elicited perceptible changes in overall plant community composition and distinct responses by individual plant species. In the woody layer of the plant community, release from winter and spring wild ungulate herbivory increased densities of larger Wyoming big sagebrush (Artemisia tridentata, ssp. wyomingensis) at the expense of small sagebrush, while disturbance associated with either cattle or wild ungulate activity alone was sufficient to increase bare ground and reduce cover of biological soil crusts. The perennial bunchgrass, bottlebrush squirretail (Elymus elymoides), responded positively to release from summer cattle grazing, and in turn appeared to competitively suppress another more grazing tolerant perennial grass, Sandberg's blue grass (Poa secunda). Grazing by domestic cattle also was associated with increased non-native species biomass. Together, these results illustrate that ungulate herbivory has not caused sagebrush plant communities to undergo dramatic state shifts; however clear, herbivore-driven shifts are evident. In a dry, perennial-dominated system where plant community changes can occur very slowly, our results provide insights into potential long-term trajectories of these plant communities under different large herbivore regimes. Our results can be used to guide long-term management strategies for sagebrush systems and improve habitat for endemic wildlife species such as sage-grouse (Centrocercus spp.).

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Artemisia / growth & development*
  • Biomass
  • Cattle
  • Herbivory*
  • Mammals*
  • Seasons

Grants and funding

This work was supported by the Deseret Land and Livestock http://www.deseretlandandlivestock.com/ (MER); Utah Agricultural Experiment Station http://uaes.usu.edu/ (KEV); Utah Agricultural Experiment Station Mineral Lease Funds (MER); USDA-ARS Pollinating Insect Research Unit http://www.ars.usda.gov/main/site_main.htm?modecode=20-80-05-00(CMM); and the National Science Foundation DEB grants 0087201 and 0244247 (MER). The funders had no role in data collection and analysis, decision to publish, or preparation of the manuscript. With the exception of Deseret Land and Livestock, the funders had no role in study design. Deseret Land and Livestock identified general locations for the exclosures so we could focus the study on known winter ungulate range. However, the specific locations of different treatments were chosen by the authors.