A new study shows that trees that have experienced many wet years may struggle to cope with dry spells, while young trees that have never experienced abundant rainfall may be better equipped to deal with prolonged drought.
The findings come from a twenty-year study of trees in the Rhône Valley in the Swiss Alps. For the study, scientists irrigated Scots pines growing in a mature forest and compared them to plots fed only by rainfall. Researchers found that Scots pines grew faster on irrigated plots.
Eleven years after the study, scientists stopped supplying water to half of each irrigated plot. The previously irrigated pines, they noted, appeared severely stressed by the drought, even more so than the trees that had never been irrigated.
Trees that survive drought change in ways that allow them to better cope with future dry spells. They develop smaller, stronger cells and grow deeper roots to absorb scarce water, while their leaves shift away from harvesting sunlight to storing water.
It appears that the previously irrigated trees overreacted to the decrease in water. Compared to the trees that had never been irrigated, the previously irrigated trees were better adapted to drought, and those adaptations significantly slowed their growth. The findings, published in the American Journal of Botanysuggest that trees with a ‘memory’ of wet periods may cope poorly with a warmer world.
To write The conversationthe authors offer a ray of hope, noting that in most temperate forests, young trees grew up during a time of chronic drought. “Those young trees, which have survived an endless dry period, will form the forests of the future,” they say. Today’s young trees “may be better prepared for the world as humans have shaped it.”
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