HEAT: Plant Die-off

 

Last updated 7/16/2021 at 11:15am



Hello Borrego Springs. This is a wake-up call. Living in Borrego and the amazing Sonoran Desert that surrounds the community, you probably thought the desert was heat tolerant and immune to Global Warming. Hey, it’s already a desert, how bad can it get?

Well, according to a newly released report, it’s not just bad, it’s getting worse. Alarming new research shows 40 percent of Anza-Borrego Desert plants are dying due to the increase in temperatures, and prolonged Drought. Or if you thought that science-based climate change was a hoax, this report probably won’t change your mind. However, since these plants have no replacements, there will be lots more sand in which to bury your heads.

After analyzing more than three decades of satellite data, a group of scientists from the University of California, Irvine, found a 37.5 percent decline in native vegetation in a study that encompassed 5,000 acres of the Southern California Sonoran Desert, from the Mexican Border north across Anza-Borrego Desert State Park to Palm Springs, where plants such as creosote bush, yucca, Ocotillo and Mesquite grow.


“Plants are dying and nothing is replacing them,” said Stijn Hantson, a project scientist at UCI’s Department of Earth System Science, and lead author of the study. “It looks to be a striking loss for shrubs.”

The team’s findings, published in the Journal of Geophysical Research: Biogeosciences, corroborate those of previous field studies in which different groups documented drought-related, die-offs of dryland plants in the Southwest, with some species completely disappearing from their habitat – possible local extinction events that shouldn’t happen under more moderate, normal hydrologic and temperature conditions.


Mark Jorgensen, a Borrego resident, last Park Naturalist for California State Parks at Anza-Borrego, and Resource Ecologist, with 36-year park career as the Superintendent of ABDSP, believes that desert natives and even zero scape landscaping, are being dangerously stressed by the current rise in desert temperatures.

“I’ve seen exposed, dying tree roots, even among desert-adapted trees and shrubs, like California Junipers. The park has lost the Elephant trees on the lower levels of the trail. Going up S2, and Montezuma Grade, one can see the progression of the dying shrubs on the lowland, which appears to be the edge of the sustainable habitat, to the healthier varieties on higher grades,” Jorgensen said.

The air pressure on land creates a higher surface temperature, creating radiant heat at ground level. When the air temperature is 124 degrees, the ground temperature, which plants and animals, and barefoot humans experience, is a scorching 175 – 190º.

“Natural rocks, and other things, like cement, asphalt roads, roof tops, buildings, and carbon from cars and electrical uses, refract, reflect and fuel the heat. Ground cover shrubs, plants and trees provide shelter and some relief from the burning sun for the desert’s insects, reptiles, toads, birds, and mammals that struggle to make it through the hot months,” explained Jorgensen.

In addition, landscaping, native plants and trees shelter each other and keep ecosystems intact.

“Scientific projections for the climate crisis in the deserts are not so much about an increase in summer temperature highs, but a much more prolonged season, like six months, of intense heat,” Jorgensen pointed out. “We already have creeping warming with seasonal highs of 100 degrees from May to September.”

In the Sonoran Desert and nearby landscapes, the scientists found, vegetation cover declined much more sharply than Drought or wildfires alone could explain. Satellite observations between 1984 and 2017 showed “widespread” declines in perennial vegetation cover, the researchers wrote, especially in lowland deserts.

The reduction of vegetation cover in deserts, the researchers say, is the result of considerable year-to-year variability in rainfall in conjunction with climbing temperatures associated with anthropogenic climate change. The Drought conditions causing the mass plant die-off has changed the way the ecosystem responds to climate shifts. Notably, it seems to have broken down the once-predictable relationship between rain and vegetation cover.

The importance of heat surprised even the researchers and former ABDSP superintendents.

The research suggests “dry land ecosystems are at a breaking point- and may be more susceptible to climate change than expected. Many plant species in desert ecosystems have adaptations that allow them to withstand high temperatures, making this observation somewhat unexpected,” they wrote.

The hope had been that desert plants would stand a better chance against climate change, as they come equipped with drought-tolerant features. But the research is proving this is definitely not the case. As the authors noted, the plants exist right on the edge of what’s habitable, so any environmental shift toward greater extremes is likely to be detrimental. “They’re already on the brink,” Hantson said.

The researchers were particularly surprised at the role played by the higher heat due to human-caused climate change in driving plant loss.

Jorgensen, along with Kathy Dice, current chair of the Borrego Water District Board of Directors and retired Superintendent of the ABDSP, also expressed concern about what they believe to be an escalating rate of plant reduction.

“I knew things were disappearing, but not that it was so bad. A decrease of 37.5 percent is profound. I’m convinced about climate change worldwide, but we live in the desert, where I believed there would be a lesser impact,” Dice said.

She also stated that the change was happening quicker than she expected.

“We are going to have to take a hard look at what we want Borrego to look like in 20 years, and how to adapt to the realities of climate change. Human adapted landscaping in Borrego Springs now needs extra moisture to get through the summers. Helping the Park is infinitely more complex since global warming is just that – a worldwide problem requiring global solutions and intervention. Between the majority of people, who are not educated about what’s happening to the planet, and the climate change deniers, who for political or economic reasons, refuse to act, the risks of escalating damage to the desert are great,” Dice said.

“I’ve also noticed changes in plant life, with many species disappearing and not recovering. It’s already a desert. I wonder, how much more land can it take? I know the desert is millions of years old and will survive and change, but as for people, those not in touch with water – Mark Twain’s description of the early west: ‘Whiskey is for drinking. Water is for fighting over,’ may be an apt warning about the future.”

In the study, plants on the dry side of nearby mountains saw a slower rate of decline – only 13 percent, likely due to the slightly lower temperatures.

The situation in mountains where pines and oaks grow are also less stark, which the researchers attribute to more rain. The Santa Rosa Mountains, for example, see an average of 770 millimeters of precipitation a year, while regional deserts experience as little as 73 millimeters annually. The work doesn’t identify specific species that are dying, but complements efforts by researchers who are examining ocotillo, creosote bush, yucca, mesquite and other Sonoran Desert plants.

More bad news: It’s not just the Southern California deserts at risk due to rising temperatures. Extreme heat waves with triple-digit, record setting temperatures are currently happening throughout the United States, with New York, Oregon and Washington scorching under a “Heat Dome.” Canada, the Arctic, and Siberia are melting under here-to-fore unknown highs of 117 – 118º. June’s unexpected sunstroke worldwide is causing high risk health conditions and significant death rates; economic chaos, particularly with agriculture; impacting already serious natural species extinctions; and recharging debates about the relationship between Global Warming and extreme weather events.

According to Jorgensen, concepts like, “Climate Change,” “Global Warming” or the “Greenhouse Effect” still aren’t part of the public dialogue in Borrego. However, they’re important discussions, taking place among members of the Technical and Environmental Advisory Committees of the Borrego Basin’s Stipulated Water Sustainability Plan. Jorgensen added that members serve to ensure that the Watermaster, in implementing the court-approved agreement, does not harm or further jeopardize the native desert ecosystems. In her role, presiding over decisions of one of the main water users – the Borrego Water District – Dice agreed.

Satellite or remote sensing technology has really revolutionized what we can study without setting foot on the ground,” explained Lynn Sweet, a University of California, Riverside conservation biologist, who studies desert plants just to the north of the study area. “Many changes in where plants occur, how dense they are, and their conditions can be detected using the different wavelengths of light reflected and absorbed on the ground. This is a really neat application of the technology.”

This, of course, has serious ramifications for the Desert’s non-human inhabitants.

In a cascading series of impacts, “pollinator insects that rely on the vegetation for food and water, lizards that eat bugs and the larger animals that rely on the reptiles, including already endangered species, are struggling harder as a result of plant loss,” Hanston and Randerson explained.

With the state’s 11-year Drought, the necessary refueling and recharging of the Park’s ecosystems by previous rainfall patterns isn’t happening, Jorgensen became concerned about the wildlife. Fearing the Bighorn Sheep were losing access to their traditional sources, he had a number of rainwater collectors built in different areas throughout the Park. Despite these efforts, the count of the magnificent animals is down, and two of the watering holes have gone dry. Tragically, for the man, who became a park ranger because of his youthful fascination with the magnificent animals, at one of the sites, four bighorn sheep were found dead. Dehydrated, they died of thirst, because they didn’t know any other place to find water.

Jorgensen is currently working with California State Parks and Department of Fish and Wildlife officials on a plan to have helicopters drop water into the collectors, replacing what nature can’t provide.

“Human activity took away their water, and we have an ethical and humane responsibility to the bighorns to provide the water they need to survive,” Jorgensen reasoned.

“The study is valuable because it provides an overall view of plant biomass and how it’s being impacted by climate change, which includes warmer temperatures, a decline in precipitation and a doubling of long-term droughts lasting three or more years,” Palm Springs veteran desert ecologist James Cornett, said. “Because it relies on satellite imagery, it cannot show which species of plant are being most impacted. That’s where boots-on-the-ground fieldwork comes into play to show us exactly which plant species are in trouble.”

Having both the groundwork and the sky viewpoint “doubles our confidence in saying that some very bad things are happening in our desert environment,” Cornett added.

Long-term plant monitoring is now underway in Anza-Borrego so that researchers can see what happens to vegetation cover as the years unfold, since changes in plant communities can affect many things, from how well soils retain water to how much food there is for desert animals.

“People are truly living the old story about the frog and boiling water. Put a frog in a boiling pot, and it will jump out to safety; put the frog in cool water, and slowly turn up the heat so that the frog will not notice what is happening, until it’s too late, and it will roast to death,” Jorgensen said.

“It will be unfortunate, if we fail to pay attention to the fact that the weather is getting hotter; and we can’t wait to make changes and save our glorious desert and planet after we have passed the boiling point.”

Here in Borrego Springs, early spring and summer heat waves with below average rainfall, forecast another year of extreme hardship and loss for fragile desert life, leaving some to ask, “Have we passed the boiling point?”

Funding for the work came from Anza Borrego Desert State Park, the California Strategic Growth Council and the UC National Laboratory Fees Research Program. The research originated from a collaboration among scientists in UCI’s Department of Earth System Science, including Hantson and co-authors James Randerson and Michael Goulden; and scientists in UCI’s Department of Ecology and Evolutionary Biology, including Sarah Kimball and Travis Huxman.

 
 
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