Cars, cows, and checkerspot butterflies: nitrogen deposition and management of nutrient-poor grasslands for a threatened species

Published source details Weiss S.B. (1999) Cars, cows, and checkerspot butterflies: nitrogen deposition and management of nutrient-poor grasslands for a threatened species. Conservation Biology, 13, 1476-1486.
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This study is summarised as evidence for the following.

	Action	Category
	Other biodiversity: Use grazers to manage vegetation Action Link
	Other biodiversity: Exclude grazers Action Link

Other biodiversity: Use grazers to manage vegetation

A before-and-after study in 1995–1998 in a serpentine grassland in the San Francisco Bay Area, California, USA, found that grass cover decreased and forb cover increased after grazers were reintroduced, but the threatened, endemic, Bay checkerspot butterfly Euphydryas editha bayensis did not recolonize the site. Invertebrates: Populations of the Bay checkerspot butterfly did not increase in the three years after grazers were reintroduced. Plants: In 1995, after cattle had been excluded for five years, grass cover was 75%. In 1998, after cattle had grazed for three years, grass cover was 45%. Cover of Plantago erecta (a host plant of the Bay checkerspot butterfly) did not increase after cattle were reintroduced, but cover of forbs (non-grass herbs) increased from 10% to 30%. Methods: Grazers were reintroduced to one site in Silver Creek in 1995. Postdiapause butterfly larvae and plant cover were sampled in 1995–1998 (sampling methods not reported).
Other biodiversity: Exclude grazers

A replicated, before-and-after site comparison in 1991–1998 in serpentine grasslands in the San Francisco Bay Area, California, USA, found that populations of the threatened, endemic, Bay checkerspot butterfly Euphydryas editha bayensis declined in sites with cattle excluded, but also declined in cattle-grazed sites. One host plant of this butterfly had lower cover in sites with cattle excluded, compared to cattle-grazed sites, and two non-native grasses had higher cover. Invertebrates: Numbers of Bay checkerspot butterfly larvae first increased, but then decreased to local extinction, after cattle were excluded from two sites in Silver Creek (excluded from 1989 and 1992 onwards, respectively; maximum: 75,000 larvae in 1993; minimum: 0 in 1995–1997). However, decreases were also seen in 1994–1997 at nearby sites from which cattle were not excluded (Coyote Ridge, maximum: 38,000 in 1994; minimum: 0 in 1997). Decreases, but not local extinction, were seen in a different site from which cattle were excluded from 1985 onwards (Kirby Canyon, maximum: 135,000 in 1992; minimum: 25,000 in 1997). Plants: Lower cover of Plantago erecta (a host plant of this butterfly) was found in sites with cattle excluded, compared to cattle-grazed sites (Silver Creek and Kirby Canyon: 4–8% cover; Coyote Ridge: 16% cover). Higher cover of total grasses (54–62% vs 25–35%), and also some non-native grasses (Lolium multiflorum: 45% vs 18–32%; Avena sp.: 18% vs 2%), was found in sites with cattle excluded. No differences were found in the cover of Vulpia microstachys, Bromus hordaceous, and B. rubens (about 2% cover for each). Methods: Postdiapause butterfly larvae were sampled in 1991–1997 in three sites with cattle excluded (two in Silver Creek, one in Kirby Canyon) and three sites with cattle (Coyote Ridge). Plants were sampled in 1996.