Photo credit: AAAS
Drought is preventing trees from fighting climate change
In terms of curbing climate change, trees are man’s best friend. As they grow, they pull carbon dioxide out of the air and convert it into sugars that add bulk to their trunks. This carbon storage ability is so well-known it has spurred an international tree-planting movement to slow global warming.
But drought could compromise the ability of trees to protect us from climate change, according to a new study. Scientists have shown that drought slows tree growth for many years beyond the initial dry spells, creating what researchers call a “drought legacy.” And scientists trying to predict climate change “could be really missing the boat,” if they are not including the effects in their computer models, says Melinda Smith, a community ecologist at Colorado State University, Fort Collins, who was not involved with the work.
To determine the true toll of droughts, Princeton University ecophysiologist William Anderegg and colleagues turned to the International Tree-Ring Data Bank, which stores 100 years or more of tree-ring data from more than 1500 nontropical areas of the world. In these temperate zones, trees lay down new trunk each summer but go dormant in winter, creating a pattern of rings that track the intensity of annual growth. The broader the area between two rings, the more productive the tree and the more carbon it stores.
Examining tree-ring data from Europe, North America, and parts of Asia between 1940 and 2008 (a time with reliable weather data), researchers discovered that, in trees with at least 25 years’ worth of rings, these layers were thinner than usual not just in years of droughts, but on average for 3 or 4 years afterward. Scientists had known droughts could damage tree tissues, leaving a drought legacy, but they didn’t know how long the legacy lasts. As they report online today in Science, trees growing in drier climates, such as the U.S. Southwest, fared the worst.
Read the full article: SCIENCE MAG.