How useful are streamflow-related indicators for assessing forest degradation? A Canadian forest hydrology perspective

Streamflow regulation, such as moderation of peak flow and augmentation of low flow, is considered an important ecosystem service provided by high integrity forests. Forest management activities, including harvesting and road construction, can contribute to forest degradation by reducing the capacity of forests to provide streamflow-based ecosystem services. Due to the importance of water-related forest ecosystem services, many frameworks for sustainable forest management include indicators that are intended to capture how forest disturbance may affect water resources, such as streamflow. However, streamflow-related indicators often do not involve direct streamflow observations which, for countries like Canada, is partly due to a paucity of streamflow monitoring for forested watersheds. These indicators rely instead on various proxy metrics, such as percentage of watershed area that has been harvested. In addition, many of these indicators are vaguely defined, difficult to quantify, and may not reflect current understanding of forest-water interactions. We review current and emerging streamflow-related indicators of forest degradation from the perspective of Canadian researchers working in the field of forest hydrology. From this viewpoint, we highlight the strengths and weaknesses of these indicators and discuss potential areas of future research that could inform more rigorous and robust approaches for forest degradation assessment and reporting using streamflow-based indicators.