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

Published source details Runquist E.B. (2011) Butterflies, cattle grazing, and environmental heterogeneity in a complex landscape. The Journal of Research on the Lepidoptera, 44, 61-76.
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This study is summarised as evidence for the following.

	Action	Category
	Reduce grazing intensity on grassland by reducing stocking density Action Link

Reduce grazing intensity on grassland by reducing stocking density

A replicated, site comparison study in 2003–2004 in 27 oak and conifer woodland and shrubland sites in Oregon, USA (Runquist 2011) found that at sites with no or low grazing intensity there was lower overall butterfly species richness in one of two years and higher abundance of butterflies with grass host plants in both years compared to sites with moderate grazing, but butterfly density and community evenness were not affected by grazing intensity. In 2003, but not 2004, butterfly species richness was lower along transects with low grazing intensity (0–15%) than those with moderate intensity (30–45%) (data presented as log species richness). There was no difference in species richness between any other grazing intensities (15–30%, 45–60% or 60–75%). Grazing intensity did not affect butterfly density or community evenness (data not provided). Butterflies with grass host plants were more abundant along transects with 0–30% grazing intensity than 30–45% intensity, but there were no differences between abundances at any of the other grazing intensity categories (data presented as log abundance). See paper for individual species results. Twenty-seven butterfly transects of varying lengths were conducted in April–September 2003 and 2004 either in oak woodland and shrubland or in meadows in areas dominated by mixed-conifer forest. Sites were cattle-grazed from May–November. Each transect was surveyed for butterflies 0–7 times in 2003 and eight times in 2004. In 2004, at each transect, cattle grazing intensity (0–75%) was estimated by measuring the height of that transect’s dominant cattle-palatable plant at every metre for 50 m, calculating the average height across the transect’s sampling points, and comparing this to the height of a reference ungrazed plant of that species from the same transect to calculate a grazing intensity percentage.

(Summarised by: Eleanor Bladon)