As storms become stronger, it might be possible to keep more trees standing if they are planted closer together
Trees that grow close together can survive powerful storms and prevent wind damage by supporting each other.
Our knowledge of how wind damages trees has been limited by a lack of real-world experiments using the wind speeds seen in destructive cyclones.
Kana Kamimura at Shinshu University in Japan and her colleagues were monitoring two different plots of Japanese cedar trees, one of which had been thinned to assess whether giving individual trees more room to grow made them more vulnerable to wind damage, when typhoon Trami unexpectedly hit in early September 2018.
“I set the plot in 2017 and the typhoon came in 2018, and half of my plot was destroyed,” says Kamimura. “So the [study] is kind of lucky, but also kind of unlucky.”
Kamimura and her team measured the stress forces experienced by the trees before, during and after the typhoon, and surveyed the resulting damage. The plot that hadn’t been thinned kept all of its trees, while the sparser plot lost many.
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The researchers think that the tight spacing helped protect the trees in the plot that wasn’t thinned by dissipating the force from the wind through collisions between branches of neighbouring trees. This stopped the force travelling into the sensitive stem and roots below, where it might help uproot trees.
They also found that the trees that did fall in the thinned plot didn’t fail instantly but over time, like a piece of metal that’s repeatedly been bent back and forth before finally breaking.
Understanding how far apart to space trees in plantations could be important for the timber industry, and for efforts to plant forests for carbon offsetting.
“If you’re in an area which has a high risk of wind damage, you really want to manage your forest in a different way,” says Barry Gardiner at the European Institute of Planted Forest in France, who was one of the study’s authors.
“Even though specific to this Japanese coniferous plantation, I think there’s wider relevance there about how to manage woodlands at a time of climate change and increased extreme wind events,” says Yadvinder Malhi at the University of Oxford, who wasn’t involved in the study.
It will be important to conduct more experiments with different amounts of thinning, says Kamimura. “If we can find a method for how many trees we should remove, it will be very helpful for foresters managing forests.”