THE majestic old trees of the western US are disappearing twice as fast as they were three decades ago, and climate change is probably to blame.
of the US Geological Survey and colleagues collected data from old forests on the West Coast as well as in Arizona, Colorado and Idaho. In 87 per cent of the study sites, trees are dying faster than replacements can spring up. The Pacific Northwest was worst affected, with death rates doubling every 17 years (Science, ).
鈥淲e may only be talking about annual tree mortality changing from 1 per cent to 2 per cent, but the implications are huge,鈥� says Mark Harmon, an ecologist at Oregon State University in Corvallis.
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The team believes the rise in temperatures across the region is the main culprit. It could be drying the trees out, or encouraging parasites such as beetles and fungi. If warming kills trees it could create a vicious circle, releasing even more carbon dioxide into the atmosphere.
They considered the theory that suppressing forest fires ultimately increases tree mortality rates, but trees are dying faster even on plots that have not burned 鈥� and thus not had fires suppressed 鈥� for 200 years.
at Yale University says the findings are interesting but hard to extend to the US East Coast or Europe, where old, unmanaged forests are rarer.