Monday, August 3, 2009

PS 20-167: Decaying roots: An overlooked component of soil carbon pool

G. Geoff Wang, Huifeng Hu, and David H. Van Lear. Clemson University


Much more of the world’s carbon is stored in soils than in vegetation or in the atmosphere. Forest soils contain about 75% of the soil carbon.  However, scientists may have underestimated the quantity of carbon stored in soils because they have overlooked carbon stored in decaying root systems.  Decaying roots of harvested trees, before they are fully decomposed and incorporated into soil, are not accounted for in most C budget models because they are not a part of live biomass or detritus pool. Decaying root systems of harvested trees may be a significant component of below-ground C storage, especially in those managed forests that are harvested repeatedly in short-rotation (e.g., loblolly pine plantations in southeastern USA). 


Based on destructive sampling of root system of loblolly pine trees harvested at different years, we estimated that root systems of harvested trees contained about 24% of the below-ground carbon soon after harvest and about 11% of below-ground carbon 10 years later. Based on roundwood output data published by US Forest Service between 1995 and 2005, we estimated belowground biomass at the time of harvesting. We then calculated remaining root biomass at any given years since harvesting using the decay function developed in the study for the root systems of harvested trees.  Our calculations indicated that C storage in decaying roots of loblolly-shortleaf pine forests in South Carolina, harvested between 1995 and 2005, ranged from 38.37 to 73.72 Tg, depending on methods used to convert roundwood outputs to the belowground biomass at the time of timber harvesting.clusions