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hubie [soylentnews.org] writes:

Trees' tolerance, watered down [ucr.edu]:

Despite recent, torrential rains, most of Southern California remains in a drought. Accordingly, many residents plant trees prized for drought tolerance, but a new UC Riverside-led study shows these trees lose this tolerance once they're watered.

One goal of the study was to understand how artificial irrigation affects the trees' carbon and water use. To find out, the researchers examined 30 species of trees spread across Southern California's urban areas from the coast to the desert. They then compared those trees with the same species growing wild.

"We found that, particularly as you move toward the desert regions, the same species of urban trees use much more water than their natural counterparts, even trees considered drought tolerant," said study lead and former UC Riverside botany graduate student Peter Ibsen, currently with the U.S. Geological Survey.

[...] Drought tolerant trees often restrict their water use to protect themselves from drying out when temperatures rise. However, with the exception of ficus, the irrigated trees all increased their water intake.

"Generally, they're not conserving it," Ibsen said. "Given the extra water, they will use it all."

[...] In these and other ways, urban trees are so unique in their behaviors that they can be classified as having their own distinct ecology. "Urban forests are different than anything else on the planet, even though all the species are found elsewhere on the planet," Ibsen said.

[...] It is unclear whether overwatered trees can regain their ability to thrive in drought conditions if the water is removed. Also unclear is the specific amount of water people ought to give their trees in order to for them to thrive and retain their best attributes. Both issues are areas the researchers will be studying, going forward.

For now, Ibsen recommends that gardeners interested in conserving water refrain from planting their drought tolerant tree on an irrigated lawn. "If you're buying a tree that's meant to be drought tolerant, let it tolerate a drought," he said.

Journal Reference:
Peter C. Ibsen, Louis S. Santiago, Sheri A. Shiflett, et al., Irrigated urban trees exhibit greater functional trait plasticity compared to natural stands [open], Bio Lett, 2023. DOI: https://doi.org/10.1098/rsbl.2022.0448 [doi.org]

Original Submission