KVIG Informative

The Joshua tree’s range almost perfectly outlines the Mojave Desert itself. Scientists studying how that range is shifting are using the tree as a living instrument for measuring climate change across the region Las Vegas calls home.

Joshua trees are spindly, tree-like yucca plants so closely tied to this specific desert that their historic range roughly maps the Mojave’s boundaries. The U.S. Geological Survey has spent years building species distribution models for both the western and eastern Joshua tree species, using satellite imagery combined with field verification across more than 670,000 grid cells to map exactly where the trees grow now and what environmental conditions define that range.

What the Models Predict A foundational 2011 USGS study modeled how Joshua trees would respond to projected climate warming and concluded the species could go extinct across much of its current range by the end of the century absent significant intervention. A follow-up 2012 study from UC Riverside’s Center for Conservation Biology reached a similar conclusion about the overall threat, but identified specific places within and surrounding Joshua Tree National Park that could serve as long-term climate refugia, pockets of habitat buffered enough from warming to support the species even as the broader range contracts. The National Park Service’s own climate change research confirms that as conditions grow warmer and drier, Joshua trees and other Mojave species are expected to shift toward higher elevations that receive more rainfall.

Researchers at UC Riverside’s Center for Conservation Biology have already documented Joshua trees dying out in the lower, hotter portions of Joshua Tree National Park, alongside similar die-off in pinyon pines and junipers at those same lower elevations. A 2018 study published in the journal PLOS ONE, led by researchers Samuel St. Clair and Joshua Hoines, examined how Joshua tree reproduction and population structure vary across the Mojave’s climate gradients, using a widespread flowering event in 2013 to study how the species responds to the desert’s naturally high year-to-year precipitation variability, now compounded by longer-term climate shifts.

It’s Not Just the Trees The Mojave desert tortoise, which ranges across the desert north and west of the Colorado River through southern Nevada, southeastern California, and northwestern Arizona, faces its own well-documented climate pressure. Research modeling potential habitat loss found desert tortoises could lose between 66 and 88 percent of their suitable habitat in the Joshua Tree National Park region under a moderate climate change scenario. Severe drought is expected to push species including the desert tortoise and desert bighorn sheep toward higher elevations with more reliable rainfall, according to the National Park Service, the same directional shift already documented in Joshua trees themselves.

Some of the most valuable data collection now comes from ordinary visitors rather than professional researchers alone. Joshua Tree National Park runs a citizen science program built around the iNaturalist app, asking visitors to log observations of mesquite, young Joshua trees, young single-leaf pinyon pines, and blooming wildflowers, data park scientists use to track how climate change is affecting the range, reproduction, and seasonal timing of the park’s plants and animals over time. A comparison of professional biologist surveys against citizen scientist surveys on the same research plots found volunteers documented greater species richness and more individual lizards than the professionals working alone, evidence that broad public participation can meaningfully strengthen this kind of long-term ecological monitoring.

The Joshua tree’s fate is tied directly to the broader Mojave ecosystem that Las Vegas sits inside. As the region’s dominant tree species shifts range, dies back at lower elevations, or finds refuge in higher pockets of habitat, the lizards, birds, and other desert species that depend on it are being pulled along the same gradient. Scientists studying this one plant are, in effect, tracking the health of the entire desert that surrounds the valley.