Dead forests in California

Warmer temperatures and longer dry spells have killed thousands of trees and shrubs in a Southern California mountain range, pushing the plants' habitat an average of 213 feet up the mountain over the past 30 years, a UC Irvine study has determined.
http://www.sciencedaily.com/releases/2008/08/080811195317.htm

In what claims to be the first study to show directly the impact of climate change on a mountainous ecosystem, the Irvine team have studied the location of plants, and shown what could occur globally if the Earth's temperature continues to rise. Their findings also has implications for forest management, as it rules out air pollution and fire suppression as main causes of plant death.
White fir and Jeffrey pine trees died at the lower altitudes of their growth range in the Santa Rosa Mountains, from 6,400 feet to as high as 7,200 feet in elevation, while California lilacs died between 4,000-4,800 feet. Almost all of the studied plants crept up the mountain a similar distance, countering the belief that slower-growing trees would move slower than faster-growing grasses and wildflowers.