Excessive Livestock Grazing
Excessive livestock grazing causes the degradation of native plant communities, a reduction in habitat values for native wildlife species, the degradation of aquatic ecosystems, and the impairment of vital ecosystem processes. In the past century and a half, grazing on the forests of the Sierra Nevada forests has been excessive and largely unsustainable. These practices have destroyed native vegetation, degraded meadow habitat and eroded streams. Today’s levels of grazing are significantly reduced from historical levels but grazing still impacts sensitive habitats and species throughout the Sierra Nevada.
Plant communities and ecological systems that are important for biological diversity including riparian zones, aspen groves, montane meadows, aquatic habitats, and oak woodlands, continue to be exposed to unsustainable levels of livestock grazing. Scientists in the Sierra Nevada Ecosystem Project (SNEP) determined that “over-grazing in mountain meadows is a threat to many rare species that are restricted to these habitats.” The rare and ecologically important vegetative communities found up and down the Sierra, such as riparian areas and high mountain meadows, evolved without the exposure and pressures of livestock grazing.
In areas where livestock have been permitted to graze for decades to a century or more, native wildflowers that exemplify Sierra meadows have virtually been eliminated. In their place, coarse non-native grasses and common weeds have taken over.
Sadly, these riparian and meadow systems are considered key livestock forage areas by decision-makers in the U.S. Forest Service. Recent studies have indicated that the vast majority of grazed forage came from these sensitive areas while the overall acreage of these areas constituted less than five present of the total allotment acreage. Cattle are naturally drawn to these lush habitats that provide not only forage but also water and shade in the hot Sierran summers. Once these areas have dried out on late summer, the continued presence of cattle in these sensitive habitats causes significant destruction by trampling overexposure. Precipitation events following this intense usage lead to increased erosion and sedimentation in area aquatic ecosystems.
Livestock grazing has significant impacts on the growth of new tree growth as well. It leads to compacted soils and the removal of leaf litter, making conditions difficult for the germination of acorns and new growth. Acorns and young oak saplings are also consumed by livestock reducing the likelihood of regeneration of multiple tree species. Many species dependent on aquatic, riparian, and meadow habitats, are at risk from the presence of livestock, including the willow flycatcher whose nests are trampled by livestock using these meadow habitats. The imperiled Yosemite toad is also threatened by the continued destruction of the stream habitat by livestock grazing.
Livestock grazing also negatively affects native species by transmitting diseases to wild animals. One bacteria found in domestic sheep has had a devastating impact on the Sierra Nevada bighorn sheep. Amazingly, allotments found within bighorn sheep habitat are still permitted to allow livestock grazing even though this known threat to the species exists.
Researchers have also found dangerously high levels of E. coli bacteria are common in streams and other aquatic and riparian habitats where livestock are permitted in the Sierra Nevada.
While livestock grazing in Sierran meadows and riparian areas is permanently altering or eliminating habitat for dozens of unique and beautiful plants and animals, the threats to Sierra Nevada willow flycatcher and the Yosemite toad are particulary urgent. Read more about these species here on our website.
Derlet, MD, R.W., J.R. Carlson, PhD. 2006. Coliform Bacteria in Sierra Nevada Wilderness Lakes and Streams: What Is the Impact of Backpackers, Pack Animals, and Cattle? Wilderness and Environmental Medicine, 17, 15-20. (54KB PDF)
Kattelmann, R., and M. Embury. 1996. Riparian Areas and Wetlands. Sierra Nevada Ecosystem Project: Final report to Congress, vol. III, Assessments and scientific basis for management options. Davis: University of California, Centers for Water and Wildland Resources, 1996. (523KB PDF)
Ratliff, R.D. 1985. Meadows in the Sierra Nevada of California: State of Knowledge Gen. Tech. Rep. PSW-GTR-84. Berkeley, CA: Pacific Southwest Forest and Range Experiment Station, U.S. Forest Service, U.S. Department of Agriculture; 52 p. (2MB PDF)