The lush green corridors created by Fremont cottonwoods along Arizona’s waterways are more than just a scenic display. These trees, with their golden autumn leaves and signature fluffy seeds, play a vital role in the ecosystem by providing shelter and sustenance for a variety of wildlife species.
Fremont cottonwoods thrive naturally below elevations of 6,600 feet but are also popular choices for ornamental planting due to their resilience to both desert heat and mountain cold. A critical aspect of their survival is their ability to cool themselves through leaf evaporation, much like humans perspire. However, this cooling mechanism requires a consistent water supply to the roots.
In July 2023, a heatwave prompted researchers at the Phoenix-based Desert Botanical Garden to investigate how Fremont cottonwoods withstand extreme temperatures and drought. The study involved four genetically distinct groups of trees, with half receiving ample water and the other half experiencing restricted water access.
Throughout the intense heat conditions, researchers closely monitored leaf temperatures using sensors. The results were telling: cottonwoods with limited water experienced significant leaf loss across all genetic groups, particularly those adapted to cooler climates. Conversely, trees with sufficient water maintained cooler leaf temperatures and sustained minimal damage.
The implications are clear: as future climate models predict higher temperatures and prolonged droughts, Fremont cottonwoods could face severe challenges if water sources dwindle.
This Earth Note was written by Diane Hope and produced by KNAU and the Sustainable Communities Program at Northern Arizona University.
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