Dartmouth Study - Soils Can Release Carbon For Decades After Forests Are Logged Off
Soil plays a big role in the global carbon cycle, but how much or how quickly forest soil carbon pools decline after logging is poorly understood. This may have serious implications for how carbon emissions from deforestation are accounted for. The U.S. Forest Service, for example, currently operates under the assumption that forest soil carbon pools don’t change whatsoever after logging. According to a study by researchers with Dartmouth College that was published in the journal Global Change Biology Bioenergy last September, however, the carbon stored in mineral soils, which lie underneath the organic soil layer, is released for decades after a forest is cut down.
The study’s lead author, Dartmouth doctoral candidate Chelsea Petrenko, was inspired by the previous work of her co-author, environmental studies professor Andrew Friedland, which showed that the greater disturbance to a forest, the lower the soil carbon pool would be. “That study led us to ask: does soil carbon storage not only vary with disturbance intensity but also with time after disturbance?” Petrenko told mongabay.com.
So she and Friedland took mineral soil cores from 20 forests in seven different regions across the northeastern U.S. and compared the amounts of carbon present in samples from forests logged 5, 25, 50, 75 and 100 years ago. They found no substantial difference between soil carbon pools in newly cleared forests versus those that had regrown to maturity. But they did find an inverse relationship between the time since a forest was cut down and the amount of carbon still stored in its mineral soil.
“It is not surprising that forest clearing affects below-ground processes given what we know about ecosystem biogeochemistry,” Petrenko said. “When a forest is cleared, the aboveground biomass, which would have become part of the soil eventually, is removed from the system. That is a considerable amount of carbon and nutrients to remove, and eventually the signal from that disturbance will be measurable in the soil.” The researchers chose to center their study in the northeastern U.S. for good reason: it is a region that has experienced "intense logging" for the past four centuries, according to studies. Most primary forest in the area is now gone, but logging pressures still continue, with Global Forest Watch data showing nearly a million hectares of tree cover were lost from an area of the U.S. spanning Pennsylvania to Maine from just 2001 through 2012, totaling about two percent of the region's tree cover. It should be noted that this data also includes tree plantation harvesting, so may not entirely represent deforestation.
EDIT
http://news.mongabay.com/2015/0311-gfrn-gaworecki-soil-releases-carbon-for-decades.html
