Scorching saguaros: Climate extremes are killing cactuses
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Extreme heat and drought have led to high saguaro death rates. Photo: Mario Tama/Getty Images
The combination of extreme heat and sustained drought in the Sonoran Desert is taking a toll on our iconic saguaro cactuses, researchers found in a newly published study.
Why it matters: If the plant's population declines at the same rate seen recently, the saguaro cactus will not be able to sustain itself, according to the report.
The big picture: The researchers looked at how the especially intense weather seen across the Sonoran Desert in 2020 and 2021 — the hottest and driest spell on record to that point — impacted giant cactus species (namely organ pipes and saguaros) in metro Phoenix and Baja California Sur.
- They found a direct link between diminished plant health and extreme weather.
Zoom in: In Phoenix, the researchers evaluated 1,000 saguaros at the Desert Botanical Garden and found they had elevated stress and mortality rates after 2021.
- The garden, which has been tracking saguaro health for a decade, saw saguaro death rates hover between 1-2% from 2015 to 2020. That jumped to 7% in 2023.
- About half of the garden's saguaros receive irrigation, and those cactuses fared better.
- Older cactuses saw higher stress and mortality rates, whereas juvenile ones proved more resilient.
The intrigue: Cactuses are often thought to be among the heartiest of Southwestern plants, but some of their desert adaptations might put them at a disadvantage to survive particularly hot and dry summers, Next Generation Sonoran Desert Researchers director and the report's lead author Benjamin Wilder told Axios.
- For instance, saguaros have adapted to have an extremely shallow root system so they can quickly soak up ground-level rainwater that would otherwise evaporate before sinking into the dirt. But when there is no rain, their roots aren't deep enough to reach stored water.
- Additionally, cactuses' lack of leaves puts them at risk for "sunburns," or what researchers termed "scorching," which permanently impairs the plant's photosynthesis system.
What we're watching: Phoenix and the Sonoran Desert region at large have continued to see abnormally hot and dry summers since the 2020-21 period scientists evaluated.
- With climate change, the likelihood of these extreme weather conditions will only increase.
What's next: Wilder told us that even though the research revealed some painful truths, there's power in knowing how climate change is affecting our local environment.
- He said he's hopeful that further research will show cactuses developing adaptations to survive the more intense weather. He said he was encouraged by the higher survival rates among younger saguaros.
Arizonans can help scientists further their research by participating in the Desert Botanical Garden's annual saguaro census. Residents are encouraged to photograph cactuses in their neighborhoods through the iNaturalist app throughout May.