California Sierra Nevada Mountains
Famously hiked by John Muir and a favorite place of Teddy Roosevelt, the Sierra Nevada mountain range is a birthplace of America’s modern conservation movement. Sculpted by glaciers, the California Sierra Nevada Mountains’ topography (from upper montane to alpine forests), climatic zones, geology and soils are highly variable. It is also an area where frequent wildfires are natural. This variability has led to many endemic species (found nowhere else) and a great diversity of plants and thousands of mountain meadows that support a rich diversity of birds and amphibians. The ecosystem’s high-mountain snow pack melt regulates the region’s water cycle. But higher temperatures are reducing snowpack and shifting snowmelt earlier, putting species at risk in this global biodiversity hotspot.
A Home for Threatened and Endangered Species
California’s Sierra Nevada Ecosystem is home to ~570 vertebrate wildlife species: 290 birds, 135 mammals, 46 reptiles, 37 amphibians, and 60 fish. Of these, 80 birds, 40 mammals, 10 reptiles, 20 amphibians, and 30 fish are on California’s Special Animals List. Twenty-six are endemic to the Sierra Nevada. Sierra Nevada mid and high elevations provide the only habitat for the Sierra Nevada mountain yellow-legged frog, the Yosemite toad, and the Sierra Nevada bighorn sheep. The headwaters of the rivers that start in the Sierra Nevada sustain threatened and endangered fish.
Climate Change Threats
The ecosystem is rapidly warming, having more winter rains instead of snow and experiencing an earlier snowmelt with less snowpack. This is disastrous for amphibians—more than half of Sierra Nevada’s 30 native species have declined. Yellow-legged frogs (reduced to 7 percent of their range), which are tadpoles for 3-4 years, require the snowpack to provide enough water to keep ponds from drying in summer or freezing in winter. Yosemite toads—with crashing populations even in Yosemite National Park—rely on spring snowmelts for pools to lay eggs and for survival.
The Sierra Nevada bighorn sheep is losing mountain meadows where it browses as tree lines move higher and seasonal droughts increase. The American pika, adapted to cold alpine conditions, is intolerant of high temperatures and is disappearing from lower elevation sites in the eastern Sierra Nevada. Climate change exposes pikas to heat stress in the summer as they try to forage and disperse, and to cold stress in winter as they lose the insulating snowpack that protects them from cold snaps. As temperatures warm, pikas will be pushed further upslope until they have nowhere left to go. The reduced snowpack impacts threatened and endangered fish that rely on downstream cold-water flow. (See California Bay Delta profile.)
Needed Conservation Measures
This ecosystem is heavily impacted by climate change, but also population growth, recreation, and changing land use. Most of its mountain meadows—the keystones of the ecosystem—have been altered by grazing, mining, logging, fire suppression, water uses (e.g. dams) and invasive species. Reducing these impacts is essential to build ecosystem resiliency. An under-utilized conservation measure, restoration of mountain meadows, will help species adapt and will provide Californians with water when they need it most. Scientists and nonprofits are exploring comprehensive mountain meadow restoration, reducing pollutants, and increasing forest cover to help combat climate change.
In addition to landscape efforts, there are important opportunities to minimize threats to individual species, for example, the removal of nonnative trout from high Sierra lakes and reduction of transmission of chytrid fungus to protect the yellow-legged frog, limitation of introduced fish, pesticides and cattle grazing to protect the Yosemite toad, and reduction of the threat of disease transmission from domestic sheep to protect the Sierra Nevada bighorn sheep.