A growing world population demands more wood and fiber, much of which is harvested from intensively managed forests. In these forests, tree growth as well as post-harvest land cover changes can be easy to see, but an invisible part of the management process has captured the attention of scientists and university collaborators with the U.S. Forest Service Eastern Forest Environmental Threat Assessment Center. Following a study published in the November 2015 issue of Forest Ecology and Management, researchers concluded that high forest productivity in managed forests often comes at the expense of carbon storage in soils.
The researchers reviewed current global datasets that allowed them to compare characteristics of managed and unmanaged stands. (Data indicate that, on average, managed forests are about 50 years younger and have about 50 percent less biomass.) They also examined variables in managed forests such as nutrient availability, soil disturbance, and stand age and structural disturbance, including removal of harvested wood as well as biomass left behind to decompose.
Some significant differences in forest structure and carbon stocks in standing trees became apparent. “We discovered that carbon is allocated differently between plant parts in managed forests, with relatively greater aboveground productivity and lower belowground carbon storage,” says Asko Noormets, a North Carolina State University scientist working with the Eastern Threat Center and the study’s lead author. “The greater frequency of harvests and physical disturbance of soils in managed forests results in higher soil respiration and carbon loss.”
Since forests capture and store large amounts of carbon that would otherwise remain in the atmosphere as climate-warming carbon dioxide, decision makers look to forests as part of a short-term solution to lessen the impacts of climate change. As managed forests are increasingly needed to provide renewable supplies of wood and fiber, the study’s findings should be carefully considered. In the Southeast, for example, where managed plantations abound, 30 percent of forests were harvested and regrown between 2000 and 2012 to meet national and global demands for their products.
“Currently, about 7 percent of the world’s forests are managed plantations, and the area of managed forests is increasing annually, even as the total area of global forests decreases,” says Noormets. “Results from this study can help land managers develop strategies for maximizing the ecosystem services and benefits derived from managed forests, including soil carbon storage for climate mitigation.”
For more information, email Asko Noormets at firstname.lastname@example.org.