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Vegetation response to fire and domestic and native ungulate herbivory in a Wyoming big sagebrush ecosystem

Bloom-Cornelius, Ilana V.
Coupling of fire and grazing as a landscape management tool is a global phenomenon in many diverse landscapes. While grazing exclosure studies examining the effects of livestock on rangelands have provided insight into the effects of livestock grazing, wildlife and livestock have not commonly been studied in the presence of fire. Adding the influence of fire on herbivory and the effects of herbivory on fire make this a unique study. This study uses pre–established grazing exclosures on the Charles M. Russell National Wildlife Refuge in central Montana, USA that included three grazing treatments to exclude cattle and wildlife: No Grazing, Wildlife Only, and Open Grazing. A randomized complete block design with three by two factorial arrangement of grazing treatments split by fire was repeated at three sites. Vegetation cover data was collected using a modified Daubenmire method in 2010 and 2011 with percent area burned following fire. Forage quality and biomass data, herbivore attraction, and grasshopper and rabbit herbivory data were also collected. Large ungulate herbivory affected percent area burned (p = 0.0255), and crude protein increased and biomass decreased following burning (p ≤ 0.0008). Fire decreased herbaceous and woody cover in burned treatments in the year following burning (p ≤ 0.0162), though no differences were detected between Wildlife Only and Open Grazing treatments. Excluding big sagebrush, vegetation resprouted by one growing season post fire. Differences in percent area burned by grazing treatment suggest ungulate herbivory may be a driving factor in managing fine fuels in shrubland and grassland ecosystems and can potentially be important in managing fires to create a landscape mosaic. Increased forage quality immediately following fire, and the influence of grazing on fire behavior, suggests fire and grazing evolved as coupled disturbances. Dominance of sagebrush in a fire dependent community suggests historical fire return intervals may have been shorter and current levels of sagebrush were historically unsustainable. Additional studies on the interactions of native and domestic ungulates are recommended to understand potential competitive land use influences in combination with fire.