Look around at all the wood and paper products we consider essential for daily life. Now, consider the carbon stored in those products—carbon that was removed from a forest ecosystem when trees were harvested. This type of carbon storage is quite important: while it’s locked into these products throughout their useful life, this carbon is locked out of the atmosphere as a component of carbon dioxide, a climate-changing greenhouse gas.
As the world population grows, demand for tree-derived products is also increasing. To meet the demand, the area of planted forests to supply wood for products is also increasing. When compared to natural forests, harvests on planted forests equate to relatively frequent ecosystem disturbances. So how do these harvests affect the long-term carbon balance of a planted forest?
To examine this question, researchers from the Eastern Forest Environmental Threat Assessment Center and cooperating scientists from North Carolina State University (NCSU) developed a 25-year carbon budget (the budget describes the amounts of carbon entering and leaving an ecosystem) for a typical planted forest—a commercial loblolly pine plantation in North Carolina. Results were recently published in the journal Global Change Biology.
The researchers studied data from two loblolly pine plantations over 5 years and found that the ecosystems were very productive in terms of carbon that was used and stored during the growth of new plant material. However, following harvest, carbon stored in aboveground residue such as stumps and branches did not offset the loss of carbon from soil due to respiration by organisms that decompose tree roots.
Interestingly, as harvest residue decomposed, carbon was lost aboveground within about 2 years, but most of the soil carbon was lost during the third or fourth year after harvest, presumably due to roots that continued to live well after harvest. This loss of soil carbon was offset as aboveground biomass increased with regrowth of the forest. Researchers concluded that, while total soil carbon may or may not necessarily decrease throughout a 25-year harvest rotation cycle, older soil carbon contributes significantly to fluxes in a planted forest’s carbon balance.
“The results highlight the vulnerability of existing soil carbon to decomposition. However, on the positive side, keeping this carbon pool from declining seems well within the control of forest management practices,” says Asko Noormets, a cooperating scientist from NCSU and the study’s lead researcher. “It may be possible that slightly longer harvest rotation cycles and less intensive site preparation, for example, would help sustain high biomass productivity as well as long-term carbon storage in soils. We should seek to implement practices that balance the short-term economic interests with long-term environmental and societal services.”–Stephanie Worley Firley
For more information, email Steve McNulty at firstname.lastname@example.org .