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Feb

2

2010
 
 

Speedy Trees



Long-running census reveals faster forest growth

StopwatchScientists who have been observing a U.S. forest for more than two decades say that the trees are growing faster, probably as a result of climate change.

The news isn’t entirely surprising; other researchers have reported quicker forest growth too. But it hasn’t been clear whether the trees are responding to global warming or other factors, such as disturbances or changes in soil composition.

For this study, the researchers took measurements of trees from 55 plots in Maryland for 22 years. They then calculated how much the trees would be expected to grow if they were simply recovering from a disturbance. During periods when tree mass had increased, 90% of the observed growth rates were higher than expected, the team found. On average, the trees’ annual weight gain in these plots exceeded predictions by 4.15 tons per hectare.

The change probably wasn’t caused by an influx of nutrients, since soil nutrient levels have not gone up, according to the study, which was published in the Proceedings of the National Academy of Sciences. But temperatures have increased, the growing season has lengthened, and carbon dioxide levels are rising. Combined, these factors are likely responsible for the growth spurt, the researchers say. – Roberta Kwok

Source: McMahon, S.M., Parker, G.G., & D.R. Miller. 2010. Evidence for a recent increase in forest growth. Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.0912376107.

Image © slobo, iStockPhoto.com

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