Forests are the planet's biggest terrestrial carbon sinks, absorbing and storing a quarter of the world's annual emissions. Forests are also vulnerable to changes in climate, leading scientists to explore whether they can continue their sequestering magic in a warming world.
As global temperatures rise, forests face counteracting carbon processes. Warming causes dead plants to decompose more quickly, which releases carbon dioxide. But decomposition also releases ammonium—essentially fertilizer—into the soil, allowing trees to grow faster and store more carbon.
To find out which process wins out, an ecologist tracked two 10,000-square-foot plots of deciduous forest for seven years. On one plot, he installed underground cables to warm the soil by 9 degrees Fahrenheit. This hotter soil, rife with decaying plants, released significantly more carbon than did its cooler counterpart. That carbon burst was short-lived, however. As the heated soil's ammonium levels increased, trees grew faster and absorbed more carbon. By the study's end, the warm plot's trees were sequestering carbon at the same rate as the soil was emitting it.
Unfortunately, trees' growth rate is limited, unlike the rise in temperatures. Once that growth rate trails off, additional carbon released from the ground will enter the atmosphere and cause the planet to be warmed.
