Trees in the western United States are dying twice as quickly as they did three decades ago and scientists think global warming is to blame. In their surveys, ecologists found that a wide range of tree species were dying including pines, firs and hemlocks and at a variety of altitudes. The changes can have serious long-term effects including reducing biodiversity and turning western forests into a source of carbon dioxide as they die and decompose. That could lead to a runaway effect that speeds up climate change.

”The trend was pervasive across a wide variety of forest types, across all elevations, in trees of all sizes and among major species,” said Phillip van Mantgem of the US Geological Survey (USGS). ”At the same time, the rate of new establishment of trees didn‘t change.” If these trends continued, he said, forests will become sparser and store less carbon. ”It introduces the possibility that western forests could be come net sources or carbon dioxide to the atmosphere, further speeding up global warming.”

(Punchng, 26/01/2009)