Disruption and recovery of carbon dioxide and water vapour exchange over British Columbia forests after natural and human disturbance

Globally, forests are facing a wide range of disturbances that significantly impact carbon dioxide (CO2) and water vapour exchange. In British Columbia (BC), Canada, coastal Douglas-fir and interior lodgepole pine are two of the most common tree species. Led by some early studies in the 1970s, two long-term BC forest research clusters were established using eddy-covariance techniques to further investigate the disruption and recovery of CO2 and water vapour exchange in BC forests after natural and anthropogenic disturbances. By synthesizing the results and analysing the latest data, we found that harvesting Douglas-fir stands caused substantial CO2 emissions, which take about 45 years to be compensated for without nitrogen fertilization. The increase in net CO2 uptake due to nitrogen fertilization was attributed to its considerable suppression of ecosystem respiration but having a minimal effect on gross primary production while increasing aboveground biomass. Timber harvesting reduced evapotranspiration by 30 % initially but nitrogen fertilization had an insignificant effect. In the lodgepole pine stands attacked by mountain pine beetle, post-attack management strongly affected how a stand recovers. CO2 neutrality was reached in only 3–5 years after the attack when there was no intervention. Beetle-killed trees were susceptible to wind-caused treefall thereby leading to earlier CO2 emissions. However, impacts of these disturbances on lodgepole pine stand evapotranspiration were minor. Data from both clusters showed that a decrease in gross primary production and an increase in evapotranspiration occurred during the 2021 Pacific Northwest heat dome, but recovery was rapid. Long-term flux tower observations in BC have provided valuable information on stand responses to disturbance and will continue to do so as the climate changes. With advancements in remote sensing and modelling techniques, frameworks taking advantage of rich datasets to obtain urgently required knowledge for understanding forest disturbance and management should be developed.