Impacts of timber harvesting on carbon dynamics in the conterminous United States from 1992 to 2050
Characterizing the locations and intensities of carbon removal over large areas is a necessary step towards an improved quantification and understanding of the carbon cycle at local to global scales. However, spatially explicit data layers at fine spatial and temporal resolutions are not available at present. In fact, using remote sensing techniques to map the locations and intensities of biomass harvest is one of the frontiers in land change sciences. So far, regional to national estimates of live biomass loss from harvesting have largely been relied on forest inventory systems. Although the inventory-based approach is currently the most solid approach within the inventory framework itself, it relies on isolated inventory field plots and is not able to capture the details and heterogeneity of forest harvesting events on landscape. In addition, most previous studies focused on historical periods while future projections are rare. In this study, we presented a holistic approach that integrates remotely sensed data, land use change modeling, forest inventory measurements, and carbon accounting and biogeochemical models to estimate the spatial and temporal dynamics of live biomass loss from forest harvesting in the conterminous Unites States.
The total removal of aboveground biomass was estimated to be around 90 TgC/yr from 2001-2010 and was expected to increase continuously over time reaching about 140 TgC/yr in 2050. Two factors contribute to the increase: (1) increased biomass intensity because of forest growth, and (2) increased area of clearcut to meet the increasing demand on timber production. We found that the area affected by partial cutting was much larger than that by clearcut at present. Current forest inventory data suggested a bell-shaped probability of partial cutting as forests grow and the highest probability was around 20-30 years for softwood, and 50-60 years for mixed and hardwood forests. Will the partial cutting practices, especially for mixed and hardwood forests, change along forest aging across the country remains a major uncertainty in quantifying carbon sequestration in the Unites States.