Global Warming Destroys the Forests of The Western U.S.

The report, created by the U.S. Geological Survey (USGS), found that the rate of tree deaths more than doubled in the last few decades even in apparently healthy, well-established forests. The increase in tree deaths includes trees in a variety of forests, elevations and sizes. The danger of this trend is that with further tree decay their will be less forests to store carbon dioxide emissions; these emissions would then be cycled back into the atmosphere further increasing global warming.

The study hinged on the cooperation of various entities including the USGS, U.S. Forest Service, National Park Service and various academic institutions. These groups counted trees in 76 plots, each the size of two football fields, in forests across six western states and British Columbia.

The team focused on old forests, where many of the trees were between 200 and 1000 years old. Studying old-growth forests was key because they are generally less disturbed and have a wide variety of trees of different ages. In 87% of the plots, trees are disappearing faster than new trees are springing up.

The likely reason behind these deaths, according to WIRED, is that the region has warmed considerably during this period. Since the 1970s, temperatures across the West have risen by 0.3-0.5 degrees Celsius every ten years. Such warming has led to reduced snowfall, a smaller winter snowpack, and earlier spring melts. Higher temperatures could also be killing trees by jump-starting their enemies. The warmer the weather, the faster the insects and pathogens that feed on trees can grow and reproduce. These two factors could even be complementing one another as drought weakened trees are unable to fight the pathogens.

This theory was shared by the scientists behind the study who looked at a variety of factors including: air pollution, overcrowding, pests, fires and logging as the reason behind the increase. "Every way we cut the data and examined it, it looks like internal dynamics are not a significant source of the increase in mortality rates," Nathan Stephenson, a USGS research ecologist, said during a teleconference. "What we were left with was temperature," he said. "Increasing temperature was correlated with the increase in mortality rates."

According to Stephenson, the best chance of saving the forests is to stop its cause at the source. "Anyway you cut it, the best solution is to get a lid on humanity's carbon output," says the USGS ecologist and co-author of the report.

By: Alberto Ramos Cordero

Sources:

New Scientist, Time, U.S. News, Wired