Plusses: more carbon dioxide and humidity. Minuses: more heat and drought.
Climate change poses a unique set of threats to the world’s forests. Forests are vital for ecosystems, water and nutrient cycles, and carbon management, so dying trees are a worrying prospect. And increased temperatures and droughts certainly have the potential to kill trees.
But a paper in this week’s PNAS suggests that the increased CO2 and humidity that will accompany climate change may go some way toward offsetting the risks to forests—and identifies which forests are likely to fare better and worse.
Feed the tree
What kills a tree? As with humans, the options are endless, but climate change creates some specific risks. Decreasing annual rainfall in certain regions is an obvious problem, but it’s also about when the rain falls, not just how much of it does. Drought in the growing season is a bigger problem than at other times of year. Higher temperatures also mean that trees lose more water from their leaves. On the other hand, higher humidity and more CO2 in the air allow trees to operate more efficiently. That might allow them to compensate for drought and heat.
Yanlan Liu, a researcher at Duke University, led a team in modeling these different effects. The goal was to work out how they’re likely to affect the world’s forests under a range of different climate change scenarios. They estimated the impact on 13 forests from around the world, in both temperate and tropical regions. Their sample included broadleaf forests, like the deciduous forests in the eastern US and the always-green jungles of the Amazon. They also looked at needleleaf forests made up of conifers, like the evergreen forests of Canada.