Earth Equity News

Water-Stressed Trees Die Largely Because They Stop Photosynthesizing. By Gayathri Vaidyanathan, ClimateWire, January 15, 2010. "The reasons for tree mortality in a warmer, drier world have been narrowed down to three main scenarios -- greater prevalence of insects and diseases in a warmer world, the drying out of plants, and a third mechanism where water-stressed trees stop photosynthesizing, called carbon starvation. While researchers are still debating the relative merits of the three, scientists from Los Alamos National Laboratory have pointed to the last scenario as the most relevant for tree mortality. Researchers have made a concerted effort over the past few years to document tree deaths around the world. With climate models predicting up to a 4-degree-Celsius increase in global temperatures in the coming years, the impact of warmer weather on forests is unknown. 'It is likely that overall warmer temperatures, together with drought, has the potential to kill trees,' said Craig Allen, an ecologist with the U.S. Geological Survey. The ability of plants to absorb carbon dioxide from the atmosphere is a vital component in global climate change talks because forests act as natural sinks that trap carbon from the atmosphere. Tree death episodes have been noted on all continents since the 1970s because of seasonal and longer-term droughts, according to a recent study co-authored by Allen. The atlas cedar has declined markedly in North Africa following extreme drought. In Russia, 76 million hectares (187.8 million acres) of forests have been labeled as having high risk of health problems. In the United States, pine trees have declined across millions of hectares, and their mortality has been linked to droughts, according to the study."