Small-scale topographic variability influences tree species distribution and canopy throughfall partitioning in a temperate deciduous forest

At very large spatial scales, the impacts of topography, elevation, and aspect on throughfall variability are apparent. However, within relatively small catchments (<50 ha), differences in species composition induced by slight changes in elevation coupled with slope orientation, could result in sufficient canopy variability whereby throughfall hydrology would be definitively different across small gradients. This study aims to (I) quantify the differences in throughfall hydrology across small topographic gradients, (2) determine the variability of throughfall across such gradients, and (3) determine the seasonal effects on throughfall hydrology resulting from differences in species composition and growing niches. Throughfall partitioning was measured during 15 sampling periods at 4 landscape positions including 3 hillslopes with aspects facing north (NF), west (WF), and south (SF) in addition to a flat area (F) situated in the center of a 12 ha deciduous catchment. Throughfall partitioning was significantly lower on the steepest SF plot (TF = 75.0%) than on the moderately sloping NF (TF = 83.9%, p = 0.001) and F (TF = 81.7%, p = 0.037) plots. SF also had the largest degree of throughfall variability (CV = 20.1), resulting from overlapping canopies, which led to higher rates of canopy interception. NF and WF plots exhibited the largest inter-seasonal differences with decreases in throughfall partitioning of 13.2% (p = 0.013) and 12.1% (p = 0.052), respectively, and corresponded to the largest differences in plant canopy indices (PAO between seasons. Although slope and aspect were found to be distinguishing variables in our study, it was the influence of these variables on species composition that led to differences in throughfall quantity. Our study illustrates the systematic distribution of water resources across topographic positions within a relatively small forested catchment and highlights the need for additional consideration of topography-induced controls on microclimate and growing space, which ultimately influence water quality and quantity for effective management strategies. (C) 2015 Elsevier B.V. All rights reserved.