Third in an intermittent series exploring the effects of climate change on the diverse and numerous ecoregions of California.
There is a region of California where heat creates a distinctive desolation, and that desolation worsens each year. Climate change is transforming a landscape that kills unprepared hikers into one that bakes away its own vegetation.
To perceive this change firsthand, travelers need only enter Joshua Tree National Park at Oasis Visitor Center, 50 miles from Palm Springs and 107 degrees on an average July day. The park road ascends gradually beyond the visitor center, attaining a cooler plateau studded with rock formations.
What look like giant green paintbrushes stand among the high ground rocks — the saplings of Joshua Trees, the park’s namesake. In an exodus from the overheated flats, the species seeded itself at the higher elevation, taking with it the yucca moths that pollinate it, together with the rest of its ecological subsystemof plants and animals. The pollinating moths occupy the flowers of the tree, as well as the ground at its base.
Dr. Cameron W. Barrows, ecologist at the University of California-Riverside, discovered the Joshua Tree migration. He currently analyzes the many lower profile relationships among life forms in the park to determine how climate change is stressing those bonds. In 2016, he will inaugurate a study on 45 species of mammals, birds, plants, reptiles and amphibians, ranking each according to its projected vulnerability to climate change. Researchers will apportion a segment of Joshua Tree landscape and monitor the presence of these lifeforms over a period of years. They intend to enlist the aid of citizen-scientists in order to facilitate the laborious and time-consuming legwork that the project requires.
The road leading from the Oasis Visitor Center follows a transition zone between two ecological regions, enhancing the visibility and impact of climate change. Global warming is readjusting life within the transition zone. The fiercely hot Sonoran Desert at the visitor center sends its emblematic cholla cactus into the Mojave Desert several miles up the mountainside, in evident pursuit of the Joshua Trees. This makes for an intriguing study environment for Dr. Barrows and colleagues.
A second life form that desert newcomers view as an emblem of this environment is considered vulnerable to climate change. The chuckwalla lizard, sunning on the rocks like a miniature dinosaur, reaching 18 inches in length, subsists on vegetation. Drought patterns that reduce abundance of plants place stress on the fearsome, but harmless, lizard.
Climate change at Joshua Tree is an adjustment involving death through heat and dryness, but it amounts to a redrawing of boundaries rather than a disaster. The average perso views the flight of the Joshua Trees and sees the Sonoran Desert overtaking the Mojave Desert. Dr. Barrows cautions that the entirety of a region is more than the existence of a single plant. Ecology is a science that studies patterns and admits the limits of its statistics.
“The boundaries of what we now call the Mojave Desert, climatically and biologically, will shift as a result of modern climate change. That will probably mean shifts to higher elevations and perhaps further north and west. That could mean a contraction or an expansion. The complexities of what constrain and enable movements/shifts of ecoregions, such as the Mojave Desert, exceed our current understandings.”