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• Harvesting and mountain pine beetle attack caused significant forest C losses in BC. • N fertilization of the coastal Douglas-fir stands increased NEP by suppressing R e. • Disturbances interacted as the MPB sites had accelerated treefall due to high winds. • Water vapour exchange was much less impacted by disturbances than CO 2 exchange. • The 2021 heat dome abruptly decreased NEP and increased ET, but recovery was fast. Globally, forests are facing a wide range of disturbances that significantly impact carbon dioxide (CO 2) 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 CO 2 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 CO 2 emissions, which take about 45 years to be compensated for without nitrogen fertilization. The increase in net CO 2 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. CO 2 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 CO 2 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. [ABSTRACT FROM AUTHOR]

The most recent mountain pine beetle (MPB) ( Dendroctonus ponderosae ) outbreak in British Columbia (BC), which began in the late 1990s, killed ∼54% of the mature merchantable lodgepole pine and was expected to impact gross primary productivity (GPP), ecosystem respiration ( R ) and thus net ecosystem productivity (NEP) of infested stands. Eddy-covariance (EC) measurements of carbon dioxide and water vapor fluxes have been made in an almost single-species not-salvage-harvested lodgepole pine stand in northern interior BC during the decade following beetle attack in 2006 to determine the effects on the carbon (C) and water balances. We modified the 3-PG (Physiological Principles in Predicting Growth) model to simulate the effects of MPB attack on the stand. Modifications included a sub-model for heterotrophic respiration, which originates from the decomposition of two substrates, soil organic matter and coarse woody debris from the falling dead trees, thus permitting the determination of R and NEP. The modified model was used to simulate C balance components using model parameter values mostly taken from the literature with some estimated from in-situ measurements. Modelled monthly and annual stand-level GPP, R and NEP agreed well with respective EC-estimated values during the decade following attack. Modelled annual GPP, R and NEP decreased by about 52%, 35% and 126%, respectively, in the first year following attack compared to pre-attack values. Modelled GPP and R, as well as EC-estimated GPP, showed a relatively steady increase over the following decade, while R derived from the EC measurements changed little in the first eight years after attack and then increased in the last two years. EC-estimated GPP in 2016 exceeded the estimated pre-attack value by 9%, while modelled and EC-estimated R in 2016 exceeded 2005 values by 6% and 15%, respectively. Modelled NEP indicated that the recovering stand became a C sink a year later than indicated by the EC measurements, but both modelled and measured annual NEP increased significantly between 2007 and 2016. Our observations and modelling results show that the remaining trees and the growing understory enabled the not-salvage-harvested stand to recover from insect attack within a decade, with the stand functioning as a weak, yet distinct, C sink in the last two years of the study period. This suggests that the management strategy of not harvesting attacked stands can be beneficial for the C balance of attacked stands with similar characteristics and in similar climates. [ABSTRACT FROM AUTHOR]

Tree mortality due to the recent mountain pine beetle (MPB) ( Dendroctonus ponderosae ) outbreak in British Columbia (BC) is expected to impact evapotranspiration ( E ), gross primary productivity (GPP), and snow accumulation and melt, thereby influencing ecosystem hydrology. To quantify the impact on E and GPP, we have made eddy-covariance (EC) measurements of water vapor and carbon dioxide fluxes for nine years above a lodgepole pine ( Pinus contorta var. latifolia ) stand in northern interior BC that was not salvage harvested following beetle attack in 2006. To understand the processes and determine long-term recovery of the water and carbon balances of this stand following attack, we modified the 3-PG (Physiological Principles in Predicting Growth) model to include the effects of insect attack on the stand, and modelled monthly E , GPP and water use efficiency (WUE) of the understory and overstory. The modified model was validated using the flux and climate measurements made during the nine-year period. It generally worked well with modelled annual E and GPP agreeing reasonably well with their measured values. Modelled values of annual E and GPP decreased by about 62% and 52%, respectively, between 2005 and 2007. Annual measured E remained remarkably stable for five years after the attack, and then increased by ∼13% year −1 in the last four years; however, the model indicated a relatively steady increase of ∼13% year −1 over the 9 years. On the other hand, EC-estimated GPP showed a steady recovery (∼9% year −1 ) almost returning to estimated pre-attack levels within nine years. Modelled annual GPP generally agreed with EC-estimated values as well as capturing much of the interannual variability observed in the last 4 years. Projections for the following decade, depending on expected climate change, suggested that E would slightly increase, GPP would remain relatively constant, and WUE would decrease slightly. With the decrease in E , modelled drainage ( D r ) increased significantly in the first year after attack compared to pre-attack estimates, but gradually decreased again in the following years. Measured and modelled D r decreased between 2007 and 2015 by about 28% and 49%, respectively. Projections show D r staying relatively constant for the following decade (2016–2025). Our observations that the recovery of E and GPP was faster than expected suggest that not to salvage harvest MPB-attacked stands with considerable remaining live canopy trees or understory should be a beneficial management strategy from carbon sequestration and hydrologic perspectives. [ABSTRACT FROM AUTHOR]

Over the past decade, British Columbia (BC), has experienced the largest mountain pine beetle (MPB) outbreak on record. This study used the eddy-covariance (EC) technique to examine the impact of the MPB attack on evapotranspiration ( E) and associated canopy characteristics of two lodgepole pine stands with secondary structure (trees, saplings and seedlings surviving the attack) located in central BC. MPB-06, an 85-year-old almost pure stand of pine trees, was first attacked in 2006, and by 2010, ~80% of the trees had been killed. MPB-03, a 110-year-old stand with an overstory consisting of over 90% pine and a developed sub-canopy, was first attacked in 2003 and by 2007 had > 95% pine canopy mortality. EC measurements began in August 2006 at MPB-06 and in March 2007 at MPB-03, and continued for four years. Annual total E ranged from 226 mm to 237 mm at MPB-06, and from 280 to 297 mm at MPB-03, showing relatively little year-to-year change at both sites over the four years. Increased E from the accelerated growth of the surviving vegetation (secondary structure, shrubs and herbs) compensated for reduction in E due to the death of the overstory. Monthly average daytime canopy conductance, the Priestley-Taylor ( α), and the canopy-atmosphere decoupling coefficient (Ω) steadily increased during the growing season reaching approximate maximum values of 5 mm s−1, 0.75 and 0.12, respectively. Potential evapotranspiration was approximated using a vapour pressure deficit-dependent α obtained at high soil water content. Calculated water deficits indicated some water-supply limitation to the surviving trees and understory at both sites. Rates of root zone drainage during the growing season were low relative to precipitation. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]