A new study published in Science by scientists from the USGS, USDA, and various other institutes has concluded
"Our analyses of longitudinal data from unmanaged old forests in the western United States showed that background (noncatastrophic) mortality rates have increased rapidly in recent decades, with doubling periods ranging from 17 to 29 years among regions. Increases were also pervasive across elevations, tree sizes, dominant genera, and past fire histories. Forest density and basal area declined slightly, which suggests that increasing mortality was not caused by endogenous increases in competition. Because mortality increased in small trees, the overall increase in mortality rates cannot be attributed solely to aging of large trees. Regional warming and consequent increases in water deficits are likely contributors to the increases in tree mortality rates. "
As discussed on Climate Progress, this creates another potential CO2 feedback.
As regional warming caused an increased number of trees to die, there would be less living trees to absorb carbon dioxide from the atmosphere.
Yet there would be an increased proportion of decaying trees, releasing the carbon that had been locked away inside the trees’ wood.
The denier reaction to this study, if anyone cares, is to blame the Forest Service for containing forest fires, which they conclude has allowed "bugs" to proliferate and cause this problem. The authors cover that in a BBC article.
After ruling out a variety of other possible factors, including insect attacks and air pollution, the researchers concluded that regional warming was the dominant contributor...
Warmer temperatures might also increase the number and prevalence of insects and diseases that attack trees, the team added.
From these seemingly contradictory statements I gather that while warmer temperatures might increase the prevalence of these insects, this factor ruled out as the cause of tree decrease.
I just have to laugh every time I see a denier dismiss the conclusions of a peer-reviewed scientific study published in a prestigious scientific journal for no other reason than they don't like the conclusions, and submit their ignorant opinions instead. "Yes I who have never studied anything related to forestry know the causes of this tree die-off better than these scientists who specialize in the subject and engaged in a thorough study of the matter." Dunning-Kruger in effect.
Edited by dana1981 - Fri, 23 Jan 2009 18:25:21 UTC