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Veteran desert biologist Jim Cornett was astonished to see a bright yellow and black caterpillar munching on a spiny ocotillo plant one late March day. Normally the razor-spiked plants would not be considered fine dining — or dining at all — for those sphinx moth larvae and other creatures.
But the more he looked at the stand of gangly, twisted ocotillo, best known for their fluttering red springtime blooms, the more caterpillars he saw. It was a tiny but telltale sign of the unmistakable decline of those iconic plants and others in California’s deserts due to global warming, he and fellow experts say. And animals that are hungry for water are likely to play a role.
In a pair of recently published research articles, Cornett, of JWC Ecological Consultants, describes how ocotillos and another botanical giant of the southwest desert, Washington fan palms, are succumbing to the impacts of DryerHotter weather. Joshua trees, a keystone species that is important to many animals, are also in trouble, they said.
Cornett stated that “our beloved desert plants are falling.” One less understood but likely reason, he said, is animals devouring the plants as a last-ditch effort to survive themselves. Bighorn sheep can now be seen eating ocotillo leaves during droughts. Antelope squirrels also remove their bark. Black-tailed jackrabbits remove Joshua tree bark to get at the tree’s moist interior, and desert woodrats consume their leaves.
He said that “none of these animals were ever recorded to have attacked these plant before climate change.” “In other words, indirect effects may be more harmful than direct heat and drought effects.”
By his calculations, ocotillo in Anza Borrego Desert State Park are dying at a rate of about 1% a year, meaning in a century, they’ll be wiped out. He said that he didn’t calculate similar data for Joshua Tree National Park ocotillo trees, but that he had observed higher rates of loss there.
While it is now “widely known” that extreme heat and longer, more frequent droughts “place great burdens on species, particularly plant species,” he said the role of Animals desperate for moisture — like the sphinx moth caterpillars tucking into the ocotillo in March 2017 — could be the tipping point that kills an already declining plant or population. This is the subject his December note in Pan Pacific Entomologist.
He said that the indirect effects of all wildlife, especially in deserts where animals struggle for water, are less well known. “The article describes how, for the first time, the larvae and pupae of the white-lined Sphinx moth ate ocotillo leaf to survive drought.”
Earlier that March, Cornett had spied the bright black and yellow larvae busily munching on brown primrose, their preferred main meal in that area. It was a hot, dry spring and when Cornett returned 11 day later, all primroses had either died or been replaced by new ones. Instead the larvae, as the juvenile stage of moth species are scientifically known, were busy devouring ocotillo leaves.
Cornett said, “It’s not the first time that has ever been seen.” He has been following 500 ocotillo plants in the Southwest each spring since 2009 and says it’s the first. “But it won’t be the last,” Cornett said.
He said that the sphinx moth’s ability to quickly switch food sources means it is doing well so far as weather changes. However, the state park’s consumption of ocotillo plants “places yet another burden on an already stressed iconic keystone plant.”
Cornett studies the ocotillo stand in southwest Texas. It is doing better in other areas that are slightly cooler and wetter.
Another desert biologist stated that the findings support work done by her team about future threats to ocotillo as a result of climate change.
“With a decrease in the consistency of rainfall that we’ve seen with the recent drought and potentially in the future, it could make it hard for the ocotillo stands to sustain themselves,” said Lynn Sweet, director of UC Riverside Palm Desert’s Center for Conservation Biology, in an email. “Past studies in my office have shown that this species may experience a decrease in range due to climate change that is significant. This species was ranked as moderately vulnerable. Less vulnerable than the Joshua Tree, black brush, or jojoba (a Colorado Desert species), but still quite vulnerable due to the expected range reduction.”
Both scientists agreed Joshua trees are in troubleCornett suspects that the climate change has caused thirsty animalsAgain, a culprit.
“A Joshua tree that has been established can probably withstand several years of increased heat or drought, possibly even wildfire. But not if its bark is being eaten by jackrabbits, or its leaves to woodrats,” he stated. The accumulation of all impacts, direct and indirect, is what accelerates climate change’s impact.
As for the Washington fan palms, which are unique to southwest deserts of North America, older plants are dying as traditional sources of water underground shrivel, and no new plants are taking root. That’s the finding of Cornett’s second paper, recently published in Palms, the journal of the International Palm Society.
He focused on the Seventeen Palms Washingtonia filifera population, also in Anza Borrego State Park, which has been analyzed for 104 years.
He writes that a dramatic shift in structure was observed from juvenile dominance to adult dominance. W. filifera appears unlikely, as there have been only two tentative recruits since 1984.
If conditions persist, Seventeen Palms will exterminate the species.
The site’s fan trees are in decline, and no new baby plants are emerging to replace them. This is “most likely due” to a decrease in spring flow. A decrease in precipitation, an increase in frequency and length of drought, and crustal.
displacement from earthquakes are possible factors in the reduction of
moisture availability. The moisture deficit is caused by rising temperatures.
Sweet said Cornett’s research provides important clues as they and others try to determine what is changing due to a warming climate, and what is due to more typical changes in what has always been a dynamic system.
“Long-term data sets like his repeat look at Palm density is the type of evidence we need to understand what’s happening,” she wrote. “It’s true that you need small young palms to get large, older palms, and any reduction in the number of young palms can spell trouble for the sustainability of a group of palms.”
She explained that “these oases are isolated within the landscape, and this poses a challenge for this species. Having very large leaves, these plants are strongly tied to water sources, because they evaporate so much water while doing photosynthesis. These plants are not considered a desert plant. … Any change in hydrology or recharge for the water sources will affect this species.”
It is important to monitor because it structures wildlife habitats and “is of interest to humans across its range,” she stated.
Sweet and Cornett agree it’s important to determine whether there are trends or declines in several oases to definitively tie the cause to climate changes, since changes in a single stand might also be tied to human withdrawal of water from that site, or a shift in an earthquake fault that shuts off previously available subterranean water. As part of his research on 100 years of desert plant changes, he is currently studying a second fan palm stand. He also has his own observations over the past 37 years.
Overall, Cornett said he’s been “shocked” to see “wholesale reduction of plant life” in what were “beautiful desert, vegetated flatlands.”
Watering wild plants in the desert or other direct measures are likely to fail, he said. Recognizing the loss is key and then taking action to reduce greenhouse gas emissions. Although the solutions aren’t immediate or easy, he stated, they are critical.
“I think one strategy to show people, who are surrounded with ocotillo, fan palms and people who love these items and use them as business stationery, this is not something that China is doing halfway across the world,” he stated. It’s happening right now, right here.
Cornett will present a Zoom talk on Joshua trees imperiledWednesday, January 26th, from 3:30 to 4:45 p.m. via Palm Springs Library
Janet Wilson is senior environment reporter for The Desert Sun, and co-authors USA Today’s Climate Point newsletter. Climate Point is available for free to subscribers. Here: You can reach her at [email protected], or @janetwilson66 via Twitter
