Plants Are Dying in California’s Deserts, and ‘Nothing Will Replace Them’
In normal times, it is natural to assume that desert plants can withstand adversity. After all, these robust species developed to withstand protracted periods of heat and drought. They are capable of accepting it.
However, these are not typical times. A new research analyzing almost three decades of satellite footage over southern California finds that plant life has plummeted by more than a third in portions of the massive Sonoran Desert in recent decades.
The results indicate that between 1984 and 2017, plant cover in Anza-Borrego State Park – California’s largest state park – decreased by 35%.
“Plants are dying, and nothing’s replacing them,” says Stijn Hantson of the University of California, Irvine. “It looks to be a striking loss for shrubs.”
Above: An ocotillo forest in Southern California’s Anza-Borrego Desert.
While the findings are alarming, they are not entirely surprising.
Numerous studies have documented drought-related vegetation loss in arid regions of the southwestern United States in recent years — most notably in the Sonoran Desert, which crosses California, Arizona, and parts of Mexico.
“These vegetation mortality events seem to exceed natural variability in background mortality rates, as some [dryland plant]species have experienced up to 100 percent mortality, possibly leading to local extinction,” Hantson and his co-authors note in their new research.
Despite these dire warnings, it is still unclear how climate change is causing plants to die out in dryland ecosystems, which span more than 40% of the Earth’s terrestrial area.
The researchers used Landsat satellite photos to seek for spectral patterns in the Anza-Borrego State Park terrain, where sunlight reflected by plant leaves indicates how green a region is.
The findings indicated a particularly extensive drop in permanent vegetation cover in lowland deserts – which are dominated by creosote bush (Larrea tridentata), several cactus species, and mesquite (Prosopis sp.) in some locations – over the last four decades.
The researchers report that losses were significantly smaller at higher elevations, which are covered by montane woods, juniper and pinyon woodlands, chaparral, and high desert vegetation.
The researchers report that 87.1 percent of the study area demonstrated a negative trend, with the die-offs attributable to a combination of rising temperatures and decreased rainfall during extended drought conditions – both of which are linked to human-caused global warming.
The researchers write, “The observed trends are consistent with the hypothesis that warming temperatures have caused a long-term increase in water limitation,”
“This is especially clear across the lowland deserts, which are the driest areas of the study domain, and is superimposed against high levels of interannual variability in precipitation.”
The findings suggest that plants that typically grow in hot, arid environments – which are renowned for their ability to withstand extreme environmental conditions – are now being pushed to their limits, with their harsh habitat causing them to be among the first plant casualties on the frontlines of climate change.
“They’re already on the brink,” Hantson observes.
Indeed, the research reveals that lowland desert areas may already have crossed a “ecological threshold” around the turn of the century, resulting in widespread vegetation death as a result of increasing temperature extremes combined with decreased precipitation.
What this means for the future of dryland plants is unknown, but the indicators thus far are not positive, threatening to undermine our trust in the resilience of arid ecosystems worldwide.
“The desert might be more fragile than people assume,” Hantson told The Academic Times.
“It really seems like the vegetation is going to take a long time to recover, if it ever recovers, under the new climate conditions.”
Journal of Geophysical Research: Biogeosciences published the findings.