Fax requests will be filled within 24 hours. Although widely seen an ecological no-no, grazing turns out to be essential to a threatened butterfly in the San Francisco Bay Area. This conservation twist is due to connections between the butterflies, cows and cars, according to new research presented in the December issue of Conservation Biology. The basic story is that cars and other smog sources deposit extra nitrogen on nutrient-poor grasslands in the San Francisco Bay Area. This extra nitrogen enhances the invasion of non-native grasses, which displace the plants that Bay checkerspot butterflies depend on.
Cows help the butterflies by eating the non-native grasses, which allows the native plants to grow.
Serpentinitic grasslands have more than 100 species of native plants, several of which are endangered. Weiss discovered that grazing benefits Bay checkerspot butterflies by studying several serpentinitic sites in south San Jose. The sites had been grazed for decades but when grazing ceased at two of them in the mid-1990s, the butterfly populations there rapidly went extinct. In contrast, butterfly populations persisted at a site where grazing continued. The most obvious difference between the grazed and ungrazed sites was that the latter quickly became overrun by non- native grasses such as wild oats and Italian ryegrass.