Disturbance suppresses the aboveground carbon sink in North American boreal forests

Climate change is altering vegetation and disturbance dynamics in boreal ecosystems. However, the aggregate impact of these changes on boreal carbon budgets is not well understood. Here we combined multiple satellite datasets to estimate annual stocks and changes in aboveground biomass (AGB) across boreal northwestern North America. From 1984 to 2014, the 2.82 x 10(6) km(2) study region gained 434 +/- 176 Tg of AGB. Fires resulted in losses of 789 +/- 48 Tg, which were mostly compensated by post-fire recovery of 642 +/- 86 Tg. Timber harvests contributed to losses of 74 +/- 5 Tg, which were partly offset by post-harvest recovery of 32 +/- 9 Tg. Earth system models overestimated AGB accumulation by a factor of 3 (+1,519 +/- 171 Tg), which suggests that these models overestimate the terrestrial carbon sink in boreal ecosystems and highlights the need to improve representation of fire and other disturbance processes in these models. Disturbance regimes from fire, drought, harvest and insects will probably intensify in the future and under climate change. Despite partial offsets from regrowth, disturbance from fire and harvest reduces carbon uptake and storage in boreal forests, impacting the strength of this carbon sink.

Automated summary

The study found that aboveground biomass in boreal northwestern North America increased from 1984 to 2014, with losses from fires partly compensated by post-fire recovery, while losses from timber harvest were partly offset by post-harvest recovery. Earth system models overestimated biomass accumulation, indicating a need to improve representation of disturbance processes. Disturbance regimes like fire, drought, harvest, and insects are likely to intensify in the future due to climate change, impacting the carbon uptake and storage in boreal forests.