Forest harvesting and hydrology in boreal Forests: Under an increased and cumulative disturbance context

Boreal forests cover about one-third of the global forested area and are under rapid alteration due to increased natural and human-induced forest disturbance, which have important impacts on forest carbon cycling, hy-drology, biodiversity, and many other ecological characteristics, processes, and functions. In this review, we focus on how forest harvesting affects hydrological processes in boreal forests within the context of increased and cumulative forest disturbance across various spatial scales. At the stand level, harvesting affects snow processes (i.e., snow interception, snow water equivalent, ablation, and snowmelt), decreases evapotranspiration (ET) and water use efficiency (WUE), and has negative impacts on soil dynamics (i.e., infiltration and soil moisture). These hydrological changes at the stand level can be counteractive or additive, cumulatively leading to more varied effects at larger spatial scales. In small watersheds, spring freshets (or high flows) are consistently increased following harvesting, while annual streamflow is often increased but some contradictory results are found in Siberia, Russia. These varied responses are likely dependent upon differences in energy budgets, climate, post -disturbance vegetation trajectories, and their dynamic interactions over space and time. For larger watersheds and regions, cumulative forest disturbance interacts with climate, leading to more complicated and varied hy-drological responses. Forest management implications and future research topics are also suggested.

Automated summary

This review focuses on the impacts of forest harvesting on hydrological processes in boreal forests. At stand level, forest harvesting affects snow processes, evapotranspiration, and soil dynamics. In small watersheds, spring freshets are consistently increased following harvesting. However, the responses vary in larger watersheds and regions due to the interactions between cumulative forest disturbance and climate.