Effects of Forest Conversion on Baseflows in the Southern Appalachians: A Cross-Landscape Comparison of Synoptic Measurements
Jackson, C. Rhett
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Basin forest cover is understood to influence stream baseflow in a variety of ways, most significantly via increased soil infiltration and increased evapotranspiration (ET). Extensive forestry experimentation has consistently demonstrated a negative relationship between forest cover and baseflow, attributed to ET losses associated with greater forest cover. However, it is unclear whether this relationship can be extrapolated to larger spatial and temporal scales. Spatially, larger basins may contain greater subsurface storage capacity, potentially overriding the effects of ET losses on baseflow and contributing to a positive relationship between forest cover and baseflow. Temporally, non-forest land uses may be associated with pronounced soil modification, reducing infiltration and baseflow discharge, again resulting in a positive relationship between forest cover and baseflow. This study addresses the relationship between forest cover and baseflow in mesoscale sub-basins of the upper Little Tennessee River basin in Rabun County, Georgia and Macon County, North Carolina. Ten pairs of basins ranging from three to 33 km2 were created by aligning key physical traits (e.g. basin size, aspect, and total relief), while allowing forest cover to differ within the pairs. Three series of synoptic measurements were conducted in July and August, 2005. In most pairs, greater baseflow per unit area was associated with higher forest cover, and an overall positive relationship was demonstrated between forest cover and baseflow among all twenty sub-basins. However, difference of means test results indicate a lack of statistical significance between baseflow of more forested vs. less forested stream basins. This study was conducted as a preliminary assessment for a larger study evaluating surface controls on baseflow in the southern Blue Ridge, and further research will evaluate the mechanisms driving the positive relationship between baseflow and forest cover in this region.