Credit: N. STEPHENSON

Science 323, 521–524 (2009)

Trees in western North America are dying more quickly than they used to, but there is no corresponding increase in the number of new seedling trees. Mortality rates, which are currently of the order of 1% a year, have in many cases doubled in just a couple of decades.

The trend was picked out by a group led by Phillip van Mantgem and Nathan Stephenson, both then based at the US Geological Survey Western Ecological Research Center in Three Rivers, California. The increased mortality correlates with climate change in the region, which has warmed by an average of between 0.3 and 0.4 °C per decade since the 1970s.