Study: Climate change impacts Joshua trees

March 24, 2011 at 5:35 PM
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WASHINGTON, March 24 (UPI) -- Climate change in the U.S. Southwest likely will eliminate Joshua trees from 90 percent of their current range in 60 to 90 years, a U.S. ecologist says.

Ken Cole of the U.S. Geological Survey and colleagues used models of future climate, an analysis of the climatic tolerances of the species in its current range, and the fossil record to project the future distribution of Joshua trees, a USGS release said Thursday.

The Joshua tree, a giant North American yucca, occupies desert grasslands and shrub lands of the Mojave Desert of California, Nevada, Arizona and Utah.

Joshua Tree National Park in California is named after the iconic species.

Cole and his team were able to reconstruct how Joshua trees responded to a sudden climate warming 12,000 year ago that was similar to projected warming in this century.

The study concluded the ability of Joshua trees to spread into suitable habitat following that prehistoric warming was limited by the extinction of large animals that had previously dispersed its seeds over large geographic areas, particularly the Shasta ground sloth.

Today, the researchers said, Joshua tree seeds are dispersed by seed-caching rodents, such as squirrels and pack rats, which cannot disperse seeds as far as large mammals.

The limited ability of rodents to disperse Joshua tree seeds in combination with other factors would likely slow migration of the trees to only about 6 feet per year, not enough to keep pace with the present warming climate, Cole said.

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