Estimates of carbon stored in harvested wood products from United States Forest Service Pacific Southwest Region, 1909-2012

Global forests capture and store significant amounts of carbon through photosynthesis. When carbon is removed from forests through harvest, a portion of the harvested carbon is stored in wood products, often for many decades. The United States Forest Service (USFS) and other agencies are interested in accurately accounting for carbon flux associated with harvested wood products (HWP) to meet greenhouse gas monitoring commitments and climate change adaptation and mitigation objectives. National-level forest carbon accounting has been in place for over a decade, but there is an increasing need for accounting for smaller scale administrative units, including USFS National Forest System regions and individual National Forests. This paper uses the Intergovernmental Panel on Climate Change (IPCC) production accounting approach to estimate HWP carbon storage from 1909 to 2012 for the USFS Pacific Southwest Region. For the Pacific Southwest Region as a whole, carbon stocks in the HWP pool were increasing at just below 1 million megagrams of carbon (MgC) per year beginning in the late 1940's until the early 1990's, with peak cumulative storage of 51 million MgC occurring in 1994. Net positive flux into the HWP pool over this period is primarily attributable to high harvest levels during the 1960's through 1980's. In the years between the late 1960s and 1990 timber harvest were at high but volatile levels, with high harvests of over 4.3 million ccf (3.2 million MgC) occurring five times during this period, harvest levels from National Forests have since declined to less than 1.1 million ccf (0.8 million MgC) per year, resulting in less carbon entering the HWP pool. Since 1995, emissions from HWP at solid waste disposal sites exceeded additions from harvesting, resulting in a decline in the total amount of carbon stored in the HWP pool. The Pacific Southwest Region's HWP pool is now in a period of negative net annual stock change because the decay of products harvested between 1909 and 2012 exceeds additions of carbon to the HWP pool through harvest. Together with estimates of ecosystem carbon, which are also being developed through the Forest Management Carbon Framework (ForCaMF), Regional level estimates of HWP carbon flux can be used to inform management decisions and guide climate change adaptation and mitigation efforts by the agency. Though our emphasis is on the Pacific Southwest Region as a whole, this accounting method can be applied more broadly at smaller land management units, such as National Forests.