Ocotillos are iconic Southwestern plants. With spiny, twisting limbs that can rise 20 feet, and vivid red flowers that bloom in even the driest spring, they distill the desert’s thorny allure. Ecologist Jim Cornett has conducted a long-term study of ocotillos across their U.S. range, from southern California to West Texas. What he’s learned reveals the changing fate not only of these striking plants, but of the desert Southwest itself.
Cornett began his ocotillo study in 2007.
“Even though in a sense you're focusing on a single species,” he said, “there's clearly a relationship with everything else. One of the whole things was to better understand the ecosystems in which the ocotillos survive and live and, in some cases, thrive. It's been fascinating in ways I never anticipated.”
Cornett established 10 study sites on public land, from Joshua Tree and Saguaro national parks to Big Bend and Carlsbad Caverns. And he’s returned each year, recording the number of mature and new juvenile ocotillos, as well as interactions between ocotillos and other desert lifeforms.
Basic trends were apparent from the start. Cornett’s study areas are each a single hectare – about two and a half acres. The California sites initially sustained about 30 ocotillos each, while the Big Bend site was home to more than 100. On the desert hills at Carlsbad Caverns, ocotillos were so abundant that Cornett pared back his site to a quarter-hectare, and it still had 200 plants.
But it’s not just that ocotillos are more abundant in the Chihuahuan Desert. Many new ocotillos have taken root at Big Bend and Carlsbad since 2007. But in California and Arizona, there have been no new plants.
That’s partly attributable to differing rainfall patterns, Cornett said. Unlike the western deserts, our region receives most of its rain in the summer, which supports new ocotillo growth. But extended drought also explains the ocotillos’ plight.
One observation put the situation into poignant relief. At a California site, Cornett found that antelope squirrels were chewing into ocotillo stems, to extract what little moisture they could. It killed the ocotillos, and it continued through several drought years. Then the squirrels vanished.
“So in other words,” Cornett said, “they were so desperate to get moisture, they were surviving on ocotillo stems, but eventually there weren't enough moist stems for the antelope squirrels to survive.”
Cornett’s study has brought one particular relationship into focus – that between ocotillos and hummingbirds. Hummingbirds are ocotillos’ most important pollinators. And across the “ocotillo belt,” Cornett said, ocotillo flowers are a critical food source for migrating hummingbirds. Declining ocotillo populations could rupture this ancient symbiosis.
“And so if that belt starts getting broken apart or reduced, it's going to have profound impacts on hummingbirds, to say the least,” Cornett said. “There is no other plant in that belt that produces nectar guaranteed every year.”
Climate change is the most likely explanation for the ocotillos’ plight in the western deserts, Cornett said.
“The whole thing collapses,” he said, “and that's what we're seeing now, is a kind of a slow-motion collapse that will probably take 50 to a hundred years to result in no ocotillos being in the desert regions of California.”
There’s no sign of such a decline in our region, Cornett said. Indeed, ocotillos may be extending their range here, moving into higher elevations, where less drought-resistant plants can no longer survive. As they vanish elsewhere, ocotillos may find sanctuary in Big Bend.
Deserts can seem timeless. But change is the only constant in nature. Now, human impacts are accelerating that change in dramatic ways.
This story was made possible by generous donations from supporters like you. Please consider showing your support with a contribution today.
