In the Yosemite Valley the mean minimum temperature has increased by nine degrees over the past century. Warming over the past several decades has reduced the amount of snow on the ground each spring and changed the timing and flow of western rivers. These changes are impacting trees, meadows, glaciers and mountain species in Yosemite National Park.
More climate impacts:
• The U.S. Geological Survey recently found that large trees have declined in number in Yosemite National Park, dropping 24 percent between the 1930s and 1990s. A decline in large trees means habitat loss and possible reduction in species such as spotted owls, mosses, orchids and fishers. In addition, fewer new trees will grow in the landscape because large trees are a seed source for the surrounding landscape. Smaller trees are less resistant to fire as well, so this change could result in more devastating wild fires.
• Global warming is causing major shifts in the range of small mammals in Yosemite National Park, according to research by UC Berkley biologists. High-elevation species, such as the pika, pinon mouse, ground squirrel, wood rat, and Alpine Chipmunk, have moved as much as 2,000 feet up in elevation in order to find alpine conditions. With temperatures projected to increase further, their habitat could completely disappear in coming decades.
• Snow is melting earlier in the spring and Lyell Glacier is disappearing. Historically, glaciers have boosted river water flow in dry, warm summers, and their absence could result in rivers drying up or becoming seasonal streams. Yosemite Falls, which is fed by snowmelt, typically goes dry by the end of summer, but the National Park Service predicts that earlier snowmelt because of warmer temperatures would lead to the falls drying early in the season.
• The park's expansive meadows are also at risk. Meadows rely on a combination of heavy snow cover in the winter and a brief growing season in the summer, which make it difficult for tree seedlings to survive. Warmer temperatures would make conditions more tolerable to tree species, and would lead to forests squeezing out the meadows.