Tree Mortality Rates Double in the Pacific Northwest
According to a report published in the latest issue of Science, mortality rates in seemingly healthy conifer stands in the western United States and southern British Columbia have doubled in the past several decades, and often, new trees aren't replacing dying ones.
Warmer temperatures and subsequent water shortfalls are the likely cause of the trees' increased death rate, says the report, which was co-authored by 11 academics and forestry experts and examined 76 forest plots. Warmer temperatures also reduce snowpack, prolong drought and favors insects, all which have adverse effects on forest growth.
In the Pacific Northwest and southern British Columbia the rate of tree death in older coniferous forests doubled in 17 years. That rate of increase is about 1.5 times faster than California forests, where mortality rates took 25 years to double. Mortality rates have been lowest for trees in interior states, taking 29 years to double.
According to Jerry Franklin, a professor of forest resources at the University of Washington and one of the study's co-authors, "This suggests that one, or several, northwestern tree species are sensitive to whatever is going on... An alarming implication of increased mortality rates is that the fundamental structure of these forests could be undergoing change.... My guess is that forest loss has the potential to greatly exceed forest establishment."