Butterflies, cattle grazing, and environmental heterogeneity in a complex landscape

I investigated the effects of cattle grazing intensity on butterfly species diversity relative to seven other environmental variables in the diverse Cascade-Siskiyou National Monument (CSNM) of southwest Oregon.I sampled twenty-seven transects in 2003 and twenty-nine transects in 2004 in oak savanna and mixed-conifer forests that were subject to different grazing intensities and recorded a total of 89 species across both years.Annual grazing utilization was assessed at each transect using the key-species method, which uses un-grazed palatable reference plants to create a site-specific index of utilization based on the estimated proportion of biomass consumed on grazed plants of the same species.Grazing utilization estimates ranged from low (0-15%) to high (60-75%) on a 5-point scale.Multiple environmental variables were correlated with butterfly community composition and life history characteristics, especially habitat type, plant species richness, the presence or absence of water, and vegetative cover.Cattle grazing utilization did not predict butterfly evenness or total density, and only significantly predicted butterfly species richness in 2003.However, species with grass hostplants (particularly Cercyonis slhenele) declined in abundance at higher cattle grazing utilization classes.Management activities related to grazing and butterfly conservation in complex habitats like the CSNM should target specific aspects of butterfly life history, particularly hostplant structure or associated environmental characteristics but those activities cannot be expected to have equivalent effects across species.