Attribution of net carbon change by disturbance type across forest lands of the conterminous United States

BACKGROUND

Locating terrestrial sources and sinks of carbon (C) will be critical to developing strategies that contribute to the climate change mitigation goals of the Paris Agreement. Here we present spatially resolved estimates of net C change across United States (US) forest lands between 2006 and 2010 and attribute them to natural and anthropogenic processes.

RESULTS

Forests in the conterminous US sequestered -460 ± 48 Tg C year^-1, while C losses from disturbance averaged 191 ± 10 Tg C year^-1. Combining estimates of net C losses and gains results in net carbon change of -269 ± 49 Tg C year^-1. New forests gained -8 ± 1 Tg C year^-1, while deforestation resulted in losses of 6 ± 1 Tg C year^-1. Forest land remaining forest land lost 185 ± 10 Tg C year^-1 to various disturbances; these losses were compensated by net carbon gains of -452 ± 48 Tg C year^-1. C loss in the southern US was highest (105 ± 6 Tg C year^-1) with the highest fractional contributions from harvest (92%) and wind (5%). C loss in the western US (44 ± 3 Tg C year^-1) was due predominantly to harvest (66%), fire (15%), and insect damage (13%). The northern US had the lowest C loss (41 ± 2 Tg C year^-1) with the most significant proportional contributions from harvest (86%), insect damage (9%), and conversion (3%). Taken together, these disturbances reduced the estimated potential C sink of US forests by 42%.

CONCLUSION

The framework presented here allows for the integration of ground and space observations to more fully inform US forest C policy and monitoring efforts.

Attribution of net carbon change by disturbance type across forest lands of the conterminous United States

BACKGROUND

Locating terrestrial sources and sinks of carbon (C) will be critical to developing strategies that contribute to the climate change mitigation goals of the Paris Agreement. Here we present spatially resolved estimates of net C change across United States (US) forest lands between 2006 and 2010 and attribute them to natural and anthropogenic processes.

RESULTS

Forests in the conterminous US sequestered -460 ± 48 Tg C year^-1, while C losses from disturbance averaged 191 ± 10 Tg C year^-1. Combining estimates of net C losses and gains results in net carbon change of -269 ± 49 Tg C year^-1. New forests gained -8 ± 1 Tg C year^-1, while deforestation resulted in losses of 6 ± 1 Tg C year^-1. Forest land remaining forest land lost 185 ± 10 Tg C year^-1 to various disturbances; these losses were compensated by net carbon gains of -452 ± 48 Tg C year^-1. C loss in the southern US was highest (105 ± 6 Tg C year^-1) with the highest fractional contributions from harvest (92%) and wind (5%). C loss in the western US (44 ± 3 Tg C year^-1) was due predominantly to harvest (66%), fire (15%), and insect damage (13%). The northern US had the lowest C loss (41 ± 2 Tg C year^-1) with the most significant proportional contributions from harvest (86%), insect damage (9%), and conversion (3%). Taken together, these disturbances reduced the estimated potential C sink of US forests by 42%.

CONCLUSION

The framework presented here allows for the integration of ground and space observations to more fully inform US forest C policy and monitoring efforts.

Regional assessment of boreal forest productivity using an ecological process model and remote sensing parameter maps

An ecological process model (BIOME-BGC) was used to assess boreal forest regional net primary production (NPP) and response to short-term, year-to-year weather fluctuations based on spatially explicit, land cover and biomass maps derived by radar remote sensing, as well as soil, terrain and daily weather information. Simulations were conducted at a 30-m spatial resolution, over a 1205 km(2) portion of the BOREAS Southern Study Area of central Saskatchewan, Canada, over a 3-year period (1994-1996). Simulations of NPP for the study region were spatially and temporally complex, averaging 2.2 (+/- 0.6), 1.8 (+/- 0.5) and 1.7 (+/- 0.5) Mg C ha(-1) year(-1) for 1994, 1995 and 1996, respectively. Spatial variability of NPP was strongly controlled by the amount of aboveground biomass, particularly photosynthetic leaf area, whereas biophysical differences between broadleaf deciduous and evergreen coniferous vegetation were of secondary importance. Simulations of NPP were strongly sensitive to year-to-year variations in seasonal weather patterns, which influenced the timing of spring thaw and deciduous bud-burst. Reductions in annual NPP of approximately 17 and 22% for 1995 and 1996, respectively, were attributed to 3- and 5-week delays in spring thaw relative to 1994. Boreal forest stands with greater proportions of deciduous vegetation were more sensitive to the timing of spring thaw than evergreen coniferous stands. Similar relationships were found by comparing simulated snow depth records with 10-year records of aboveground NPP measurements obtained from biomass harvest plots within the BOREAS region. These results highlight the importance of sub-grid scale land cover complexity in controlling boreal forest regional productivity, the dynamic response of the biome to short-term interannual climate variations, and the potential implications of climate change and other large-scale disturbances.