In ecology, everything is connected, but sometimes the connections are stronger than anyone anticipated. A remarkable example is that the death of forests in California can affect crops on the great plains and tree growth in the mid-Atlantic region. Not all forest loss is equal, however. A paper in Environmental Research Letters identifies the parts of the United States with the greatest potential for forest loss to cause problems much further away.
Two years ago a team led by Michigan State University demonstrated how the loss of major forest regions such as the Amazon would affect plant growth worldwide. Now the same team has looked at the same effect on a continental scale, dividing the United States into 20 regions and modeling how the loss of trees in those with significant forests would affect the others.
Of the 13 regions with enough forests to matter, the Pacific Southwest, which roughly equates to California, has the fewest trees. Nevertheless, were these to disappear entirely, decreased transpiration would dry out areas downwind, reducing plant growth over a much larger area, including the places that grow most of the nation's food. Changes to sunlight absorption and air turbulence would also have an impact.
In fact, the loss of California's forests would be more damaging than any other region, even those with much more extensive tree cover.
"Forest loss is disrupting or changing the flow patterns in the atmosphere that is leading to a slightly different summertime climate in the eastern part of the country," first author Dr Abigail Swann said in a statement. "It's very analogous to El Niño... something that's occurring that causes the atmosphere to move around, which causes these warmer or cooler conditions, or wetter and drier conditions, somewhere else."
Of course, California won't lose every last tree, so the scenario presented in the model won't occur. However, with such outsized consequences from an extreme case, it is easy to see that even moderate forest loss could be causing smaller, but still very negative, impacts elsewhere.
The issue isn't just theoretical. California has lost an estimated 130 million trees since 2010, largely through a combination of drought and insect attack. "There's some pretty extensive, widespread forest loss going on," Swann said. "The changes we made in the model are bigger, but they're starting to converge with things that we're actually seeing.”
Nor is the issue purely restricted to the Pacific Southwest. Forest loss in other western regions in the study also has negative consequences further east. In some cases, these losses are more directly under local control, being driven by logging and clearance for development, in addition to the global warming hitting California so hard.