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Warming means more forests toppled by windstorms

A fallen fir tree blocks a path in Olympic National Park in Washington state.
A fallen fir tree blocks a path in Olympic National Park in Washington state.National Park Service

By Larry O'Hanlon

Discovery News

Climate change could likely lead to more wind-fallen trees and damaged forests, say researchers studying how forests grow, mature then fall apart in big wind storms. The connections to climate change are easy to miss, however, because trees often live longer than humans.

“When you think like an ecologist and you realize that the lifespan of trees are multiples of human generations, you see that we often miss things,” said forest researcher Steve Mitchell of the University of British Columbia in Vancouver. He's also the editor of the journal Forestry, which had a special edition on wind this month.

If you know what to look for, the story of windstorms and the damage they can do is right there in the forests Mitchell said. “Wind storms leave a signature behind.”

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That signature reveals a lot about the surprisingly profound and under-appreciated role winds play in forests. With more intense windstorms expected with global warming, the story of the wind in the trees is only going to get more dramatic.

That story goes like this: when a fire or a windstorm knocks down a forest, new saplings sprout to quickly take advantage of the open space and sunlight. But competition for that light forces trees to grow tall and slender. As the forest matures, trees have brushy upper canopies with long lever-like trunks and shallow root systems – a recipe for trouble when a big storm comes along and blows on the crowns of the trees.

Trees growing together in this manner are particularly vulnerable to the wind, says Mitchell, because the trees shelter each other. When a few trees fall, more wind penetrates the stand to reach taller, even more precarious trees, and causing more to fall.

“We have wind disturbances that are so severe that entire stands are replaced,” said Mitchell. “This is very much the same logic as the disturbance regimes of fire.”

In places where trees are deliberately planted and grown for lumber, such windstorms are an economic catastrophe. Which is why foresters and climatologists in Europe, in particular, are already looking into the details of at how climate change could increase wind events -- which, along with snow loading and other things can mess up a lot of trees in very short order.

Climate models for Northern Europe, show that both mean and extreme wind speeds will increase in the southern and eastern parts of Northern Europe, according to the Finnish Meteorological Institute's Hilppa Gregow and her colleagues in a recent paper in the International Journal of Climatology.

“The change over the ocean is pronounced already in 2046–2065, over the continents in 2081–2100,” Gregow reports. Similar changes can be expected in coastal parts of the U.S. and Canada, said Mitchell, which is why the people responsible for managing forests are starting to pay more attention.