The kids aren't alright: Saplings show how changing climate may undermine forests

Monday, November 6, 2023
Photo by Alexandra Lalor. A University of Arizona-led experiment exposed different species of trees to heat and drought to study how young trees respond to climate change. After 20 weeks of drought and a one-week heat wave, this Douglas fir sapling was dry and brittle.

To gain a deeper understanding of how extreme climate conditions might lead to a large-scale die-off of the younger generation of trees, a phenomenon known as recruitment failure, Professor Don Falk, from the School of Natural Resources and the Environment at the College of Agricultur, Life and Environmental Sciences with joint appointments in the Laboratory of Tree-Ring Research and the Arizona Institute for Resilience, along with his co-authors, examined the responses of five species of 4-year-old trees to extended drought and heat. Their study revealed varying levels of drought tolerance among different species, with all species demonstrating greater heat tolerance than anticipated. The findings were published in the journal Frontiers in Forests and Global Change.

The research team collected trees from five species at different elevations in the Jemez Mountains of New Mexico. They then exposed the young trees to drought and heat conditions in a growth chamber, enabling precise control over temperature, humidity, light, and water. "Around 8 weeks in, virtually every tree was still coping," Falk explained. "However, as the drought extended to 12 and 14 weeks, the ponderosa pine seedlings began to perish, followed by the piñon seedlings, then the Engelmann spruce, and finally the Douglas fir. Surprisingly, the limber pine exhibited the greatest resilience, lasting an astonishing 36 weeks without water."

Learn more about the thresholds of young trees in drought

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Mikayla Mace Kelley
Science Writer, University Communications
520-621-1878