Professor University of British Columbia (Okanagan) Kelowna, British Columbia, Canada
Forest ecosystems can store a large amount of carbon and, thus, play an important role in global carbon budgets. However, forest carbon dynamics can greatly affect other ecological processes, and forest carbon and water are often viewed as “trade-off” relationship. Thus, evaluating forest carbon and water coupling (water use efficiency, or WUE) is critical for understanding and managing both processes. Here, we reported a study on the coupling across different spatial scales (tree-level, stand-level and watershed-level) conducted in the Montane forests situated in the interior of British Columbia, Canada. At the forest stand level, our experiment showed that thinning treatments in young, over-stocked lodgepole pine forests can significantly increase tree growth of remaining trees, while they greatly reduce water consumption. Based on simulations considering future climate change scenarios, we recommend 2500–3500 stem/ha as suitable densities for a better balancing between total carbon and water (stand transpiration). At the watershed scale, we found that severe cumulative forest disturbance has driven carbon emissions in the region, and the region’s forests continue to be a carbon source with reduced sequestration capacity. Recent wildfires in 2017 and 2018 have delayed recovery from the Mountain Pine Beetle (MPB) epidemic. Forest disturbance has driven a reduction in evapotranspiration (ET) across most of the region, and cumulative forest disturbance was a key driver of WUE. Regional WUE stabilized during the period of high disturbance, mainly due to contrasting responses by distinct climate type and their offsetting effects. It is critical to consider these interactions across spatial scales when assessing the regional forest carbon and water relationship.
