November 19th, 2016 by James Ayre
Deforestation events and mass tree deaths — whether through drought, heat, and insect infestations — can have significant effects on global climate patterns, according to new research from the University of Washington.
To put that another way, while deforestation and mass-deaths of trees can cause the complete upheaval of the local environment, effects also include significant ones on the patterns of the global climate system — and thus can lead to alterations in vegetation and dependent animals all the way on the other side of the world.
“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,” stated lead author Elizabeth Garcia, a UW postdoctoral researcher in atmospheric sciences. “The atmosphere provides the connection.”
In other words, just as the El Niño + La Niña cycle in the Pacific Ocean affects practically the whole globe in one way or another (rainfall patterns, temperatures, the carbon cycle, fish availability, etc), so too do large deforestation or tree death events. In particular, deforestation on one side of the globe can cause changes to vegetation prevalence on the other. (For generalized information on deforestation and its effects and causes see: Deforestation, Effects, Causes, and Examples, Top 10 List.)
The press release provides more: “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,” stated 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.”
With regard to the specifics of the research, the work was centered on two different regions experiencing deforestation and mass tree deaths — the western parts of North America, and the Amazon Rainforest in South America.
In western North America the tree losses as of late have primary been the result of drought, extreme heat, and beetle infestations (temps too low in winter to kill larvae). In the Amazon the losses have primary been the result of mass deforestation.
To explore the subject, the researchers utilized a climate model where drastic forest-loss occurred.
The press release continues:
“Results show that removing trees in western North America causes cooling in Siberia, which slows forest growth there. Tree loss in the western US also makes air drier in the southeastern US, 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.”
“In the second test case, removing most of the Amazon rainforest also caused Siberia to become colder and more barren, but it had a slight positive impact on southeastern US vegetation. Losing Amazon forest had a significant positive impact on the neighboring forests in eastern South America, mostly by increasing the precipitation there during the Southern Hemisphere summer.”
“The study shows that when it comes to forests, one plus one does not always equal two. Removing both forests had different impacts than the combined effects of removing the two separately, since the effects can either reinforce one another or cancel each other out.”
As the model is a new, roughly developed one, the exact with regard to the mapping of causes and effects in different locations isn’t something to take as gospel, but the general findings clearly have something to them. The researchers involved are now doing field work in order to explore, in practice, the temperature and humidity changes that comes from deforestation and mass tree deaths in different ‘types’ of forests.
The idea of this field work being to identify the locations which are most prone to being affected by such events.
“The broader idea is that we must understand and include the effects of forest loss when modeling global climate and trying to predict how climate will change in the future,” Swann noted.
The new research is detailed in a paper published in the journal PLOS ONE.
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