Forests in the eastern United States are actually growing faster than they have in the past 225 years in response to climate change, according to a new study.
For more than 20 years, ecologist Geoffrey Parker has been tracking the growth of 55 mixed hardwood forest plots at the Smithsonian Environmental Research Center in Maryland. According to his research in a newly published study in the Proceedings of the National Academy of Sciences, the forest is growing at a much faster rate than expected — two tons per acre, per year.
While that doesn’t sound like much to call home about, Parker says the unexpected growth is actually a natural response to the rising levels of atmospheric carbon dioxide, higher temperatures and longer growing seasons.
In other words, climate change.
Forests and their soils store the majority of the Earth’s terrestrial carbon. That means minor changes in their growth rate can have major effects on weather patterns, nutrient cycles, climate change and biodiversity — though exactly how is still unknown.
Parker and researcher Sean McMahon measured the growth by creating a “chronosequence,” or a series of forests plots of the same type that are at different developmental stages. Using forest plots ranging from five to 225 years old, Parker and McMahon were able to verify that there was accelerated growth in forest stands both young and old.
According to their measurements, more than 90 percent of the stands grew two to four times faster than predicted from the baseline chronosequence.
(How do they know it’s a recent phenomenon? The age groupings allow the researchers to determine that — if the rate of growth recorded was sustained for a tree’s lifetime, it would be much larger.)
Parker estimates that he and his colleagues have taken some 250,000 measurements since 1987, calculating the biomass of a tree with knowledge of its species and diameter. When the faster growth rate was discovered, the scientists were able to rule out all but the three reasons tied to climate change.
According to the scientists, in the past 22 years, carbon dioxide levels at the research center have risen 12 percent, the mean temperature has increased by nearly three-tenths of a degree and the growing season has lengthened by 7.8 days.
Parker says his study results are representative of the Eastern deciduous forest. The researchers are waiting to see if other forest ecologists find similar results in other areas of the country.
