Impact of Grazing on Endangered Species
Article by Stephanie Larson
Published November 1, 2016
|Stephanie Larson, Ph.D.|
Through the 1980’s, 1990’s, and into the early 2000’s, efforts to conserve threatened and endangered (special status) species on western rangelands often meant removing livestock ranching. Research findings, demonstration results, and failed conservation efforts in recent years involving endangered species have supported the continuation of livestock ranching and the reintroduction of grazing to some rangelands that were “protected” through grazing removal. At the landscape level, research has demonstrated that livestock ranching maintains extensive, open spaces by reducing land use conversion, fragmentation of habitat, and vegetation type conversion from invasion of brush.
Threats to native biodiversity, including special-status species, are likely to increase with a removal or a decrease of grazing. Research and experience have shown that grazing is strongly linked to maintaining habitat for some special-status species on coastal lands, while they have been inconclusive for others. Sonoma alopecurus (Alopecurus aequalis var. sonomensis) is found in eight naturally-occurring populations in Sonoma and Marin Counties; the four sites in Marin County all occur at coastal areas and are all grazed by cattle. One historic colony, that was located near Bolinas, disappeared following exclusion of cattle from the site (US Fish & Wildlife Service, (USFWS) 2002). Sonoma spineflower is found solely in a grazed pasture. A master’s thesis completed in 1992 on the ecology of Sonoma spineflower concluded that grazing of competitive, non-native plants had a positive influence on Sonoma spineflower survival (Davis 1992a and 1992b; USFWS 1998).
The relationship of grazing to some threatened and endangered species was reviewed in the U.C. Extension Report co-authored with Marin County, The Changing Role of Agriculture at the Point Reyes National Seashore. The report addresses Myrtle’s silverspot butterfly which inhabits coastal dunes, prairie, and scrub. Habitat suitability depends on numerous factors, but two critical components are the presence of its larval host plant, the native dog violet (Viola adunca), and adult nectar plants including numerous native wildflowers, as well as common weeds such as bull thistle (Cirsium vulgare) and Italian thistle (Carduus pycnocephalus). Most of the Myrtle’s silverspot butterflies documented at Point Reyes National Seashore (PRNS) have been found in areas that are grazed by cattle. Butterfly surveys done by PRNS staff in 2003 showed occurrences of Myrtle’s silverspot on 13 ranches, all of which support livestock operations (Adams 2004). Recent research on Myrtle’s silverspot (Adams 2004; USNPS 2007) documents that Myrtle’s silverspot and cattle have co-existed for over a hundred years and that the density of the nectar sources was higher in grazed areas. Biologists studying the Myrtle’s silverspot at coastal lands recorded more butterflies in grazed dunes and grasslands than in ungrazed plant communities. At time of the species’ listing, the USFWS believed that cattle grazing significantly decreased the habitat quality of the Myrtle’s silverspot butterfly. However, a five-year status review by USFWS found that the moderate cattle grazing regime currently used by ranchers on coastal lands did not significantly affect the distribution of Myrtle’s silverspot butterfly at that site. Current threats to the Myrtle’s silverspot butterfly include: urban or industrial development of any property with suitable habitat for the butterfly; poaching; small population size; the effects of reduced host and nectar plant density due to invasive plants and forbs; road mortalities during the adult flight season; and, the probable constriction of the range and distribution of this butterfly due to global climate change.
Those opposed to grazing have made claims that USFWS concluded that the grazing program was likely to adversely affect the Pacific Coast population of the western snowy plover and the California red-legged frog; however, grazing exclusion has resulted in extirpation of some populations of these species from “protected sites.” In the 1996 final listing rule for the California red-legged frog, the USFWS cited livestock grazing as a contributing factor in the decline of the subspecies. However, in its 2006 revised proposed rule, the USFWS acknowledged that: “our understanding of the threats of livestock grazing and stock pond development described in the previous final listing of the subspecies has changed… Therefore, we believe grazing helps contribute to the conservation of the California red-legged frog and its habitat.”
Rancher stewardship includes development and maintenance of livestock water sources, pest management, debris clean-up, and forage improvement. Ponds developed for livestock water provide half of the available habitat for the endangered tiger salamander (Ambystoma californiense) in the San Francisco Bay Area. These results focus on California’s annual rangeland, which is the habitat type where most of the special status species associated western rangelands are found.
In Sonoma and Marin counties ranchers have developed numerous springs and ponds to capture runoff to water their cattle. The springs and ponds help to more evenly distribute the forage consumption by cattle across a pasture; also providing drinking water for many wildlife species some of which, as discussed above, are rare species that coexist or are enhanced by grazing and the development and maintenance of ponds and springs. In riparian areas such as creeks, good range management may call for fencing to prevent heavy grazing of riparian vegetation but fencing may not always be the best solution. Ungrazed areas over time can result in a buildup of dead grass on the other side of the fence where grazing is excluded, and a thick mass of dead grass forms that prevents native plants from germinating and growing. The mass of dead grass can be overcome by invasive species such as coyote brush and Himalayan blackberry. The buildup of dead grass results in a less than healthy system, which could lead to increased erosion, reduced nutrient and water cycling and increased fire hazards. Sonoma and Marin County ranchers are well informed about practices that can be beneficial and detrimental to wildlife, water quality, and rangeland health and they have strived to implement those practices that maintain and improve rangeland and watershed conditions in cooperation with the U.C. Extension Service, U.S.D.A. Natural Resource Conservation Service, and Resource Conservation Districts.
Grazing lands provide a direct link between urban consumers and local food producers, a powerful conduit for educating the public about the importance of local food production and security. Sonoma and Marin Counties are perfect models for demonstrating how preserving family farms contribute to social, economic and ecological sustainability at local, regional and even national levels. Ranching has positive health impacts including increased food access and food security, food to local business and schools, improved health literacy and general well-being. Ranching in Sonoma and Marin Counties, albeit smaller scale, remains a local industry which provides job creation, training and business succession, and market expansion for many other ranchers and farmers.