PNNL

Abstract

Climate change is likely to impact the dynamics of forest carbon and water cycles over the coming centuries. Managed forests represent a significant fraction of land cover in many countries that ratified the Paris Agreement, investigating the potential impacts of silvicultural management on carbon sequestration seems both promising and urgently needed. Such an investigation needs to consider the physical impacts implied by harvesting as well as natural acclimation processes occurring in response to a changing environment. Here we examine the projected dynamics of forest carbon use efficiency (CUE) and water use efficiency (WUE), which both need to be considered as highly dynamical – a feature that is often neglected in climate change impact scenarios. Using a complex forest ecosystem model that represents the current understanding of forest ecosystem functioning, forced by five Earth System Models and four Representative Concentration Pathways from the ISIMIP project, we estimate future changes in CUE and WUE as a consequence of projected climate warming, rising atmospheric CO2 concentrations and management for two intensively studied forest ecosystems. Our results indicate that CUE and WUE tend to decrease in unmanaged forests due to forest ageing and accompanying physiological alterations but increase in response to increasing CO2 concentrations and as a consequence of forest management. We find that forest management strategies can significantly counterbalance the decrease in CUE and WUE projected for the next decades, while in the long-term (100 years) the benefits of this kind of management decrease substantially. We identify alternative management strategies that provide significant benefits with respect to climate mitigation compared to those currently employed. These results indicate that enhanced mitigation due to forest management is possible over longer periods of time but can prolonged using alternative forest management schemes which should be considered as valuable adaptive options.