Stemflow and soil water recharge during rainfall in a red pine chronosequence on the Oak Ridges Moraine, southern Ontario, Canada

Abstract

Summary Stemflow focusses water delivery to the forest floor in a relatively small area surrounding the tree bole, with the potential to enhance soil water contents and water recharge relative to more distal sites beneath the canopy. These stemflow fluxes may decrease as a given tree species ages due to changes in branch orientation and bark roughness, suggesting that the relative contribution of stemflow to water recharge near the bole will decline with time. The hypothesis that stemflow fluxes decline with tree age was tested in a chronosequence of red pine ( Pinus resinosa Ait.) stands in a managed forest in southern Ontario, Canada, and stemflow contributions to soil water recharge below 1 m depth were quantified. Throughfall, stemflow and sub-canopy soil water contents (0.1 m and 1.5 m from the tree bole to 1 m depth) in stands ranging from 28 to 80 years in age were studied from late-Spring to Fall in 2012, supplemented by artificial irrigations of stemflow to examine short-term soil wetting at the two distances from the bole. The hypothesized decline in stemflow with increasing tree age was not supported, and canopy cover variations and forest management exerted a greater control on inter-stand differences in stemflow fluxes. Stemflow contributions generally resulted in greater soil water recharge below 1 m depth at 0.1 m from the tree bole compared to the 1.5 m distance. This enhanced recharge was greatest for the youngest stand and differences in recharge between the 0.1 m and 1.5 m distances from the bole were likely not significant for stands between 40 and 80 years of age. Nevertheless, the relative contribution of stemflow to soil water recharge may increase in this managed forest as red pine stands give way to a mixed hardwood-conifer forest, due to greater stemflow fluxes from hardwood species in this landscape.