A new study finds that trees that have lived through many wet years struggle to cope with dry spells.
The findings come from a 20-year study of trees in the Rhône River Valley in the Swiss Alps. For the study, scientists irrigated plots of Scots pines growing in a mature forest, comparing them with plots nourished by rainfall alone. Researchers found that in irrigated plots, the pines grew faster.
Eleven years into the study, scientists stopped delivering water to half of each irrigated plot. The formerly irrigated pines took it poorly.
When faced with a severe drop in rainfall, trees change in ways that allow them to better cope with future droughts. They develop smaller, hardier cells and grow deeper roots to soak up scarce moisture. Their leaves shift away from harvesting sunlight and toward storing water.
The pines that lost irrigation overreacted. They responded as though they were going through the drought of the century, scientists said. They became highly adapted to drought, even more so than the trees that had never been irrigated, and they changed in ways that significantly slowed their growth. The findings, published in the American Journal of Botany, suggest that trees with a “memory” of abundant rainfall may struggle in a warmer world.
Writing in The Conversation, authors offer a silver lining. In most temperate woods, they say, young trees have grown up in a time of chronic drought. As a result, those trees “may be better prepared to cope with the world as humans have shaped it.”
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