by LAS VEGAS – On a sunny stretch of West Charleston Boulevard, Norm Schilling pulled his truck over to the side of the road to visit his favorite tree.
Schilling, a local horticulturist who runs a landscaping company and owns a garden store called Mojave Bloom Nursery, saved this African sumac decades ago after a severe winter caused its branches to freeze and die. With careful pruning, the tree pulled through, but this summer, a new danger threatens it: months of oppressive heat that dried up branches and left behind death in clusters of its drooping foliage.
It seems like a counterintuitive problem. The Southwest is no stranger to sweltering conditions, and desert plants and trees are drought resistant and heat tolerant. Steep, harsh environments are where they thrive.
But as climate change makes heat waves more frequent, more intense and longer, experts say the increasingly harsh conditions are testing some iconic desert plants known for their resilience – their includes saguaro cacti and agave.
“We saw damage to plants this summer that never showed heat stress,” Schilling said.
On a drive around Las Vegas, he showed the consequences.
A fake orange bush burned on a quiet residential block, with damaged spots where the sun had bleached the tissue of its shiny leaves. Down another street, a pair of turf trees were drying out, probably because they hadn’t received enough water to combat the heat. Around the corner, a large juniper tree showed signs of “major decay,” Schilling said, with dead brown leaves still adorning withered branches — evidence of recent heat damage.
“That juniper is probably close to 40 or 50 years old. She is a wonderful specimen, but she will die,” he said, then patted and kissed her rough trunk.
Then there was the range of succulents called gopher spurge a few blocks away, in which some seem burned, their branches soaked and flashed yellow in all directions.
“This species is very reliable and a very common species throughout the Valley,” Schilling said. “Some of these plants are just at the point where they’re not going to recover.”
Las Vegas has already set several heat records this summer, including the hottest day in recorded history on July 7, when the temperature reached 120 degrees Fahrenheit. That was followed by a record seven straight days at or above 115 F. Temperatures for most of June, July and August remained in the triple digits, with little relief even at night.
“The heat we’re seeing now is a new paradigm. It’s like the ground is shifting under our feet,” Schilling said.
Ecologists across the Southwest are working to figure out how different species respond to killing heat year after year and how hot is too hot for desert plants and trees.
Kevin Hultine, director of research at the Desert Botanical Garden in Phoenix, studies the effects of heat stress on the Sonoran Desert ecosystem. He and his colleagues have been anticipating an increase in saguaro cactus mortality that began in 2020 — when the state was in the midst of a severe multi-year drought — and he hasn’t let up.
“The summer of 2020 was the hottest on record until last year, and we saw a lot of die-off,” Hultine said. “It’s been steady ever since, and 2023 obviously picked up the pace even more.”
Last year, when Phoenix experienced the hottest summer in recorded history – with 31 straight days of temperatures at or above 110 F – stark images emerged of saguaro cacti that had Signature arms are lowered or completely dropped.
This year didn’t bring much relief: July was the second hottest on record in the city, and Hultine said some cacti and agave were struggling, though the situation is less dire.
Hultine said he is still trying to pinpoint the factors to blame for the saguaro die-off, including whether the greater risk comes from individual heat waves or the cumulative effects of multiple extreme summers. With long-lived plants like cacti, the full scope of the problem is often not immediately apparent.
“We may be looking at this exponential mortality curve, but it could be years before we know,” he said.
Schilling said repeated exposure to extreme heat may be a big issue: The Southwest no longer sees many cooler years between record-setting records, and temperatures stay high at night, leaving less time plants and trees recover and bounce back.
Krista Kemppinen, a senior scientist at the Center for Biological Diversity in Tucson, Arizona, said it’s the double whammy of extreme heat and drought together that seriously affects the desert ecosystem.
While it’s unlikely that saguaros are headed for extinction, she said, the heat stress observed so far is cause for concern.
“They’re one of the hardiest plants in the desert — they’re very strong,” Kemppinen said. “It is particularly worrying that they seem to be responding so negatively to extreme heat events and climate change.”
Saguaros get a lot of attention because they are a beloved symbol of the Sonoran Desert, but across the region, there are hundreds of less-studied species with smaller populations that are likely to be more negatively impacted as the t -climate change.
The heat stress and dieback observed in recent years is enough to make horticulturists like Schilling rethink what they think they know about desert ecosystems.
The changing landscape also inspired Schilling to try to raise awareness of climate change with his clients and in his community, and work with local nonprofits and government agencies to boost climate resilience throughout the Las Vegas Valley.
“We need to figure out how we fit into this environment and make it not only a healthy place to live,” he said, “but also a place that’s beautiful and sustainable and nourishing for our souls.”
This article was originally published on NBCNews.com
