Joshua trees facing extinction
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In the best-case scenario, major efforts to reduce heat-trapping gasses in the atmosphere would save 19 percent of the tree habitat after the year 2070. In the worst case, with no reduction in carbon emissions, the park would retain a mere 0.02 percent of its Joshua tree habitat.
The team's findings were published recently in Ecosphere. Project lead Lynn Sweet, a UCR plant ecologist, said she hopes the study inspires people to take protective environmental action. "The fate of these unusual, amazing trees is in all of our hands," she said. "Their numbers will decline, but how much depends on us."
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They found that Joshua trees have been migrating to higher elevation parts of the park with cooler weather and more moisture in the ground. In hotter, drier areas, the adult trees aren't producing as many younger plants, and the ones they do produce aren't surviving.
Joshua trees as a species have existed since the Pleistocene era, about 2.5 million years ago, and individual trees can live up to 300 years. One of the ways adult trees survive so long is by storing large reserves of water to weather droughts.
Younger trees and seedlings aren't capable of holding reserves in this way though, and the most recent, 376-week-long drought in California left the ground in some places without enough water to support new young plants. As the climate changes, long periods of drought are likely to occur with more frequency, leading to issues with the trees like those already observed.
An additional finding of this study is that in the cooler, wetter parts of the park the biggest threat other than climate change is fire. Fewer than 10 percent of Joshua trees survive wildfires, which have been exacerbated in recent years by smog from car and industrial exhaust. The smog deposits nitrogen on the ground, which in turn feeds non-native grasses that act as kindling for wildfires.
As a partner on this project, the U.S. Park Service is using this information to mitigate fire risk by removing the invasive plants.
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https://www.sciencedaily.com/releases/2019/07/190716073719.htm