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UCR Scientist is Studying Climate Change Risks for Joshua Trees

Benjamin Purper
Empire KVCR News

Joshua trees have inhabited the Southern California deserts for millions of years, and individual trees can live up to 300 years. Now, a new report from the University of California, Riverside claims that the famous trees could lose virtually all of their habitat to climate change by the end of the century. KVCR's Benjamin Purper took a trip to the desert to find out more.

It’s the early morning in Joshua Tree National Park, before the triple-digit heat sets in. UCR plant ecologist Lynn Sweet is showing me one of the trees that they analyzed as part of their research. 

Sweet and her team used volunteers to collect data on more than 4,000 Joshua trees. They took the coordinates of each tree, measured its sprouts, and assessed its health. 


Sweet: "So what we found is that we're already seeing the effects of climate change that has already occurred on the landscape, we're already seeing less recruitment or new trees on the landscape in some areas."


The team found that trees are already migrating north to cooler, wetter parts of the desert. That happens because seeds in the hotter, drier parts of the park tend to die off.


But the effects of climate change on these trees is only beginning. The research found that if nothing is done to stop carbon emissions, the park would retain only .02 percent of its Joshua Tree habitat.

Sweet: "However, we also modeled some scenarios where we looked at if we mitigate or if we reduce our global carbon emissions, and we found that we might have 14 percent or even 20 percent of stands persist into the future if we do something about climate change."


That’s a big if, especially as the U.S. has pulled out of intergovernmental climate agreements like the Paris Accord. But Lynn Sweet is optimistic.

Sweet: "I hope that people when they come out and look at Joshua trees or hear about this, it's something that they can grab on to and understand that the things that we do might have a real effect on whether the trees persist into the future.”

Besides lowering carbon emissions, there’s something else we can do to protect these trees: get rid of smog. 

Sweet: “There's also another aspect to this is the smog that comes in from LA and other agricultural areas and industrial areas - that smog actually is laden with nitrogen, and so the nitrogen deposits in the landscape, and that's what contributes to fire risk. So we're talking about information about where the trees might occur in the future and how to protect them, but we know that wildfire is also a risk. And so we need to - if you can mitigate the degree to which you're producing smog, that might be important because this pollution fertilizes the grass in the landscape, and that grass is tinder for wildfire, essentially.” 

Sweet says it’s important that people volunteer for citizen science projects like this one.

Sweet: "I think that the degree to which people could come out and help with this project or associated projects is great. Some people don't access to all those opportunities. Certainly volunteering in your local park, participating in other community science efforts, is really important too. There are apps people can use to document flora and fauna on their phone, that's really important, in fact we used iNaturalist observations for the modeling efforts. So we actually used observations people were doing with their phone for this effort. So I think that volunteering, also thinking about your carbon footprint." 

The full report is available on the journal Ecosphere. 


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