Friday, January 23rd, 2009

Warming Temperatures Hurt Western Trees

Sierra mixed-conifer stand in Eldorado National Forest, CA, showing several species including Douglas-fir, sugar pine, and white fir. Image courtesy of P. van Mantgem.

Warming temperatures may have led to dying trees in the western US, researchers say. Writing in the journal Science, ecologists report that tree mortality rates in the old forests of the western United States have more than doubled since 1955. Although no certain cause for the change in tree mortality has been identified, warming temperatures are a prime suspect. Temperatures have been increasing over the region -- and, the researchers say, those climate changes may have led to stress from drought or pests.

"Average temperature in the West rose by more than 1° F over the last few decades," said Phillip van Mantgem, one of the authors of the rpeort. "While this may not sound like much, it has been enough to reduce winter snowpack, cause earlier snowmelt, and lengthen the summer drought." Shifting tree mortality rates can lead to changes in the composition of the forest, making the forest more vulnerable. We'll find out more.