An insidious problem has taken hold in the forests of the American West, quietly thinning their ranks. Mortality rates in seemingly healthy conifer stands have doubled in the past several decades. Often, new trees aren’t replacing dying ones, setting the stage for a potentially dramatic change in forest structure, says Phillip J. van Mantgem, a forest ecologist at the U.S. Geological Survey (USGS) in Arcata, California. Warmer temperatures and subsequent water shortfalls are the likely cause of the trees’ increased death rate, he and his colleagues report on page 521.
“This is a stunningly important paper,” says David Breshears, an ecologist at the University of Arizona, Tucson. For years, he and others have lamented massive diebacks that occur when fungal and insect pests ravage stands of trees. “What’s harder to detect,” he explains, is any subtle but significant shift in the trees’
background death rate. “They have done a very thorough job” of documenting it.
|New growth is often failing to replace dying trees....a small difference in mortality rates can have a big effect over time. As the forest thins, ever smaller trees become dominant, affecting the land’s carbon storage capacity and ability to support wildlife|
The articles--including the one listed above and the original "Widespread Increase of Tree Mortality Rates in the Western States," Phillip J. van Mantgem, et al., Science 323, 521 (2009)--are only available to subscribers. Recommend this Post