This icon of the Mojave desert could be yet another victim of climate change.
Fri Mar 25, 2011 05:25 PM ET
An icon of the Mojave Desert, the Joshua tree may be found only at its highest or most northerly outposts by the end of the century. A new study suggests its range may shrink by 90 percent in the next 60 to 90 years as a consequence of global warming.
Ken Cole of the U.S. Geological Survey in Flagstaff, Ariz., and an interdisciplinary group of colleagues used information about the current distribution of Joshua trees combined with climate models to predict where the trees may be by 2070 to 2099.
But they also mined data from the ancient past, using fossilized dung from the extinct Shasta ground sloth -- a shaggy, Volkswagen-beetle-sized creature that consumed Joshua tree fruit as a central part of its diet. The researchers also looked at the fossilized scrap piles of packrats alive more than 10,000 years ago. With this data, the team could characterize how the tree's range changed at the time of a similar climate warming around 11,700 years ago.
The extreme dry climate of the desert has preserved sloth dung -- chock full of Joshua tree leaf fibers and fruit and seed remains -- in caves throughout the sloth's former range for at least 40,000 years. The sloths' waste accumulated in undisturbed layers over generations until the sloth went extinct 12,900 years ago. The topmost sample "represents the last dungball," Cole said.
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