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Major forest die-offs due to drought, heat and beetle infestations or deforestation could have consequences far beyond the local landscape.
Wiping out an entire forest can have significant effects on global climate patterns and alter vegetation on the other side of the world, according to a study led by the University of Washington and published Nov. 16 in PLOS ONE.
“When trees die in one place, it can be good or bad for plants elsewhere, because it causes changes in one place that can ricochet to shift climate in another place,” said lead author Elizabeth Garcia, a UW postdoctoral researcher in atmospheric sciences. “The atmosphere provides the connection.”
Just as conditions in the tropical Pacific Ocean can have distant effects through what we now understand as El Niño, the loss of a forest could generate a signal heard around the world — including by other plants.
Forest loss is known to have a nearby cooling effect, because without trees the Earth’s surface is more reflective and absorbs less sunlight, and loss of vegetation also makes air drier. These local effects of deforestation are well known. But the new study shows major forest losses can alter global climate by shifting the path of large-scale atmospheric waves or altering precipitation paths. Less forest cover can also change how much sunlight is absorbed in the Northern versus the Southern hemispheres, which can shift tropical rain bands and other climate features.
“People have thought about how forest loss matters for an ecosystem, and maybe for local temperatures, but they haven’t thought about how that interacts with the global climate,” said co-author Abigail Swann, a UW assistant professor of atmospheric sciences and of biology. “We are only starting to think about these larger-scale implications.”
The new study focused on two areas that are now losing trees: western North America, which is suffering from drought, heat and beetle infestations that span from the southwestern U.S. to Alaska, and the Amazon rainforest, which has been subject to decades of intense human development. The researchers ran a climate model with a drastic forest-loss scenario to investigate the most extreme potential climate effects.
Results show that removing trees in western North America causes cooling in Siberia, which slows forest growth there. Tree loss in the western U.S. also makes air drier in the southeastern U.S., which harms forests in places like the Carolinas. But forests in South America actually benefit, because it becomes cooler and thus wetter south of the equator.
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