Saguaros occur from Sonora, Mexico, across central and southern Arizona, all the way north to Kingman, Arizona. They can be found at elevations up to nearly 5,000 feet, growing next to junipers. The cold limits their northern extent. But saguaro survival is now being challenged at all elevations by climate change.
During periods of extreme summer heat and drought in recent years, many saguaros – especially larger plants at lower elevations – lost their arms or collapsed completely. They may live up to 200 years, but saguaros need good summer monsoon rains followed by a wet winter for new individuals to establish. Those conditions are getting rarer as the climate changes.
You can visually tell whether a saguaro is well hydrated or not. A green plant with straight, well-separated, rigid ribs indicates plenty of internal water. But if the ribs are wiggly and close together, and the outer skin is yellow or purplish, the plant is likely water-stressed.
Researchers at the Desert Botanical Garden carry out detailed saguaro ‘health surveys’ every month. They want to learn how much heat plants can endure, for how long and whether saguaros can take up enough water during the intense but short-lived storms that are replacing the frequent, smaller monsoon rains of the past.
So far, the monitoring shows that saguaros respond well to intense, short-lived rainfall; they rehydrate quickly, becoming greener and plumper. That’s an encouraging sign for the long-term survival of these iconic desert giants.
This Earth Note was written by Diane Hope and produced by KNAU and the Sustainable Communities Program at Northern Arizona University.
