Forests are feeling the heat. In places like the American West, rising temperatures and drought mean less water for trees. Now, scientists have found that thinning early in forest growth creates tougher trees that can endure climate change. What's more, these thinned forests can suck carbon out of the air just as fast as thick forests.
"When it comes to carbon storage and climate change adaptation, we can have our cake and eat it too," says Andrew Larson, forest ecologist and author of the new study. " It's a win-win."
As trees grow, they convert carbon dioxide to food and store it in their leaves, trunks, and roots. But if trees get too crowded, they compete for light and water. Removing some trees can ease the competition, letting the remaining trees grow big and healthy. But scientists worry that removing trees can reduce forest carbon storage.
To see whether the climate trade-off truly exists, scientists tapped into a long-term experiment in northwestern Montana. In 1961, U.S. Forest Service officials started the experiment in a young forest of western larch. The forest was broken up into plots. In some plots, the 8-year-old trees were thinned from tens of thousands per hectare down to 494 per hectare. These trees grew thick trunks and broad tree shades. Other plots were left alone, and the trees there grew tall and skinny as they competed for sunlight. The original study was rooted in an interest in growing timber rapidly. But the scientists at the University of Montana sprouted a new question: How did tree density (密度) influence carbon storage?
To find out, they measured tree height, diameter, and width of branches to estimate the amount of carbon stored. They also calculated the carbon contained in other plants, dead wood, and forest floor debris. The research showed total carbon was nearly the same in both forests. The un-thinned forest had more trees, but the thinned forest compensated with bigger trees.
