Long-term forest management and climate effects on streamflow
Long-term watershed studies are a powerful tool for examining interactions among management activities, streamflow, and climatic variability. Understanding these interactions is critical for exploring the potential of forest management to adapt to or mitigate against the effects of climate change. The Coweeta Hydrologic Laboratory, located in North Carolina, USA, is a 2,185- ha basin wherein forest climate monitoring and watershed experimentation began in the early 1930s. Extensive climate and hydrologic networks have facilitated research in the basin and region for over 75 years. Our purpose was (1) to examine long-term trends in climate and streamflow in reference watersheds, and (2) to synthesize recent work that shows that managed watersheds respond differently to variation in extreme precipitation years than reference watersheds. In the basin and in the region, air temperatures have been increasing since the late 1970s. Drought severity and frequency have also increased over time, and the precipitation distribution has become more variable. Reference watersheds indicate that streamflow is more variable, reflecting precipitation variability. Streamflow of extreme wet and dry years show that watershed responses to management differ significantly in all but a forest with coppice management. Converting deciduous hardwood stands to pine altered the streamflow response to extreme precipitation years the most. High evapotranspiration rate and increased soil water storage in the pine stands may be beneficial to reduce flood risk in wet years, but they create conditions that could exacerbate drought. Our results suggest that forest management can mitigate precipitation years associated with climate change; however, offsetting effects suggest the need for spatially-explicit analyses of risk and vulnerability.