Now it has been found that there is an increasing trend in the death of trees in Western American forests. Scientists have now demonstrated that the upward trend in tree deaths is both real and widespread. The overall mortality rates in these trees have doubled in the past several decades. They have been dying at a slow but increasing rate, and the scientists found that new trees are not replacing the dying ones as often. The study showed that global warming, including hotter summers, is most probably responsible for this new trend of trees dying in the Western United States. This is primarily occurring in Western forests which are essential for the stabilization of the climate and quality of life.
Tree Mortality Rates
According to the study, “Widespread Increase of Tree Mortality Rates in the Western United States”, Phillip J. van Mantgem, Nathan L. Stephenson, John C. Byrne, Lori D. Daniels, Jerry F. Franklin, Peter Z. Fulé, Mark E. Harmon, Andrew J. Larson, Jeremy M. Smith, Alan H. Taylor, and Thomas T. Veblen, Science, January 23, 2009, the death rate for these trees seems to be doubling every 17 to 29 years. This was a 52-year longitudinal study, and the trend was apparent in trees of all ages, species, and locations.
Lead author Phillip J. Van Mantgem of the U.S. Geological Survey's Western Ecological Research Center stated, "If current trends continue, forests will become sparser over time…. (and) eventually this will lead to decreasing tree size." While other causes for the tree mortality were investigated such as logging, overcrowding of trees or air pollution, the researchers concluded that it was the warmer temperature averages (about 1 degree over the study period) that is causing the changes. It seems that the death may also be partially due from a lack of water, which leaves the trees vulnerable to both disease and insects.
A shift of a percent or less may seem insignificant and the changes in the forests are minor thus far, but even a small percentage difference in the mortality rates of trees can compound and have a pronounced effect over time. As a sensitive ecosystem, it is also possible that in the future such an increase in the death rate of trees could also negatively effect the environment and cause a decline for fish and wildlife and an increase in wildfires.
The Specifics of the Environmental Longitudinal Study
The study examined data between 1955 and 2007 in 76 research plots in Washington, Oregon, California, Idaho, Colorado and Arizona. The average age of the forests in the study was about 450 years, with some as old as 1,000 years. Of the 59,736 trees counted, some 11,000 died over the period of study. Although the death rate varied, the highest was in the California Sierras at about 1.3 percent, up from 0.9 percent in 1980.
The study is recognized for its level of detail, rigor and thorough job of documentation. Often it is hard to gather data on a project of this magnitude over such a longitudinal period.
Global Warming Consequences
The effects of global warming are becoming increasingly disconcerting. North America has seen numerous glaciers evaporate. In the Arctic, melting sea ice is leaving polar bears and other arctic wildlife treading water without their critical habitat. Ecosystems are being dramatically altered by rising sea levels. There are increasingly devastating wildfires. In the Antarctic there is growing concern that a major ice shelf is breaking off. There is also concern that entire species such as the Emperor Penguins may die due to dramatic changes in their habitat. At this current rate, the death of American trees and forests will only compound these global consequences.
Resources
Widespread Increase of Tree Mortality Rates in the Western United States
The Consequences of Global Warming
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