If Trees Die in the U.S., Do South America and Siberia Feel It?

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Oddly, yes, according to a new study that highlights the complex effects regional forest die-offs have on the global climate.

By Nathan Collins

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(Photo: walker.s/Fickr)

You have perhaps heard of the butterfly effect, the idea that a butterfly flapping its wings in China can affect the weather in the United States. Though that claim is exaggerated, it does illustrate the fact that our environment is a complex system, where relatively small regional changes lead to surprising ramifications worldwide. A new study highlights another, rather more serious example: The death of a forest on one continent can have far-reaching consequences on forests around the world.

“Forest loss in hotspots around the world impacts not only local climate where loss occurs, but also influences climate and vegetation in remote parts of the globe,” University of Washington postdoctoral fellow Elizabeth Garcia and her colleagues write, yet exactly how that plays out isn’t clear.

Researchers believe forest gains and losses can have a major effect on climate—for example, adding forest in the middle northern latitudes can end up warming the entire hemisphere, which, in turn, reshapes major wind patterns like the jet stream—but the regional implications remain largely unexplored.

To fill that gap, Garcia and her team focused on two “hotspot regions,” western North America and the Amazon basin, where forest loss due to drought, heat, and insects has been particularly severe. Using the National Center for Atmospheric Research’s Community Earth System Model, they were able to simulate what would happen if forests in one or both of those regions were to be replaced with grasslands.

Those scenarios had some surprising and complicated effects, especially when considering the combined consequences of deforestation in western North America and the Amazon. For example, western North America forest loss cuts gross primary production (GPP)—roughly, how much plant matter grows in a region—in the southeastern U.S. and southern Mexico. Deforestation in the Amazon increases GPP in the southeastern U.S., while curbing GPP in southern Mexico.

Oddly, the greatest productivity gains in the southeast U.S. and southern Mexico happens when there are major losses in forests in both western North America and the Amazon. According to the simulations, western North American forest die-offs reduce relative humidity in the southeast of the continent, making it harder for plants to get the water they need from the air around them. But when forests in western North America and the Amazon decline, temperature declines and relatively stable rains actually facilitate plant growth.

“The GPP response in [southeastern North America] to remote regional forest loss demonstrates that ecological responses may differ depending on the location of forest loss and associated mechanisms of climate teleconnections,” the team writes. Similar patterns show up in Asia and eastern South America as well, the simulations suggest.

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