Joshua trees facing possible extinction by the end of the century

ST. GEORGE — Joshua trees could face near or complete extinction before the end of this century, a recent study suggests, and if this happens, it will impact other species as a result. 

Stock image, St. George News

The study, which was a collaborative effort between researchers at the University of California, Riverside, and Joshua Tree National Park, measured over 4,000 trees at varying elevations to predict their future mortality depending on the severity of climate change. 

“Our goals are to help them look at the vulnerability of the species that occur in the park to all sorts of changes,” project leader Lynn Sweet, a specialist with the Center for Conservation Biology at UCR, told St. George News. 

To determine tree mortality, biologists and nearly 100 volunteers teamed up to measure the height of the trees in order to determine their age. Then they used a computer simulation model to see where the trees might grow in the future. 

What they found is that the trees have already begun to climb to higher elevations, with adult trees dying at lower, hotter elevations. Not only have adult trees been dying, but they’ve been producing fewer new trees overall. And because Joshua tree seeds are only distributed by a select few creatures, it is difficult for the trees to quickly migrate to higher elevations, making them especially vulnerable to the effects of climate change. 

“What we expect to see is, in the coming century, in even the most optimistic scenario, we’ll start to see adult trees dying out at lower elevations – hotter areas – and then we’ll start to see young trees really only occurring in the upper elevation areas,” Sweet said.

The researchers put together a number of possible outcomes for the trees based on three different scenarios using data from the Intergovernmental Panel on Climate Change

In the best case scenario, if carbon emissions are highly mitigated, less than 20% of Joshua tree habitat will be retained by the year 2070. In the worst case scenario, wherein nothing is done to reduce carbon emissions, only 0.02% of their current range will be habitable, leaving the species nearly or completely extinct between the years 2070 and 2099, according to the study. 

“Under the worst case scenario, business as usual … we might see little to no habitat within Joshua Tree National Park and then therefore beyond Joshua Tree National Park as well,” Sweet said. “The species might be facing extinction.”

The trees won’t be the only living thing affected if they go extinct. Joshua trees are a “keystone species,” meaning that they have a large impact on other species in their environment. The trees provide shelter for a number of lizards and insects, and small rodents often eat the seeds of the Joshua tree. 

Pronuba or yucca moth in a yucca blossom, Joshua Tree National Park | Photo courtesy of the National Park Service, St. George News

Additionally, the yucca moth is the only creature that pollinates Joshua tree flowers. Should Joshua trees go extinct, the yucca moths will also die, impacting the animals that eat them as well. 

There are other factors besides temperature changes that are putting Joshua trees at risk, Sweet said.

Research has shown that air pollution is affecting the soil in the area, allowing for a decrease in native plants and an increase in invasive grasses, according to the National Park Service. These grasses allow wildfires to quickly spread throughout the landscape, putting the Joshua trees at risk, as they are easily killed by wildfires, having about a 10% survival rate.

Copyright St. George News, LLC, 2019, all rights reserved.

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