Study Shows Sierra WarmingIs Driving Small Mammals To Higher Ranges

Sharp temperature increases at high elevations in Yosemite National Park and California’s Sierra Nevada have forced many small mammals to shift their ranges at least 1,600 feet higher in search of cooler climes, according to a study in the journal Science. Conducted by scientists at the University of California Berkeley, the study relied on the detailed, 90-year-old field notes of pioneering California mammalogist Joseph Grinnell, who conducted exhaustive surveys of Yosemite’s high terrain in the early 20th century. Resurveying the Grinnell transects, the UC Berkeley scientists found that more than half of 28 small mammal species had expanded their ranges upward by more than 1,600 feet. The alpine chipmunk, for example, was common a century ago in lodgepole pine forests below 7,800 feet but is now found only at elevations above 9,600 feet. No small mammal species have yet gone extinct, but the range shifts mean that previously separated species must now compete with one another. In the central Sierra Nevada, nighttime low temperatures have risen by 5.4° F in the past century.