A study has found evidence that forests in the Eastern United States are growing faster than they have in the past 225 years, likely due to climate change.
For over 20 years forest ecologist Geoffrey Parker has tracked the growth of 55 stands of mixed hardwood forest plots in Maryland, based at the Smithsonian Environmental Research Center (SERC) in the US.
Parker’s tree censuses have revealed that the forest is packing on weight at a much faster rate than expected. He and Sean McMahon discovered that, on average, the forest is growing an additional 2 tonnes per acre annually. That is the equivalent of a tree with a diameter of 2 feet sprouting up over a year.
Forests and their soils store the majority of the Earth’s terrestrial carbon stock. Small changes in their growth rate can have significant ramifications in weather patterns, nutrient cycles, climate change and biodiversity. Exactly how these systems will be affected remains to be studied.
The chief culprit of the accelerated growth appears to be climate change, more specifically, the rising levels of atmospheric carbon dioxide, higher temperatures and longer growing seasons.
By grouping the forest stands by age, McMahon and Parker were also able to determine that the faster growth is a recent phenomenon. If the forest stands had been growing this quickly their entire lives, they would be much larger than they are.
The researchers made a list of reasons the forests could be growing faster and ruled half of them out. The ones that remained included increased temperature, a longer growing season and increased levels of atmospheric carbon dioxide.
During the past 22 years CO2 levels at SERC have risen 12 per cent, the mean temperature has increased by nearly three-tenths of a degree and the growing season has lengthened by 7.8 days. The trees now have more CO2 and an extra week to put on weight.
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