Stemflow and throughfall contributions to soil water recharge under trees with differing branch architectures

Trees whose branches slope towards or away from the bole differ in the spatial pattern of water delivery to the soil surface beneath their canopies. This study examines the implications of these differences for soil water recharge below 1 m depth in a managed forest on the Oak Ridges Moraine in southern Ontario. Throughfall and vertical profiles of soil water content at varying distances from the boles of a sugar maple and two red pines of differing ages (36 and 57 years old) were measured during rainfall inputs in the summer of 2009 and in the spring/early summer of 2010. Stemflow fluxes were estimated using measurements on nearby trees with similar morphologies. A water balance approach was used to estimate recharge at each distance from the bole, as well as for the entire sampled area beneath each tree's canopy. Throughfall was more than 1.3 times above‐canopy rainfall within 0.5 m of the bole of the sugar maple, and stemflow volumes were at least an order‐of‐magnitude greater than those for the pines in both 2009 and 2010. These focused inputs resulted in greater near‐bole soil water contents and soil water recharge in excess of above‐canopy rainfall within 0.3 m of the sugar maple bole. In contrast, both young and old pines showed no significant trends in throughfall with distance from the bole, and minor stemflow volumes made insignificant contributions to recharge near the pine boles. Recharge was significantly greater than 0 beneath the canopy of all three trees in both years and was generally similar between trees. The exception was recharge beneath the sugar maple in 2010, which exceeded that of the young red pine as a result of the former's large stemflow fluxes. Results suggest the transition from red pine plantations to mixed hardwood‐conifer stands will not alter total soil water recharge during spring and summer rainfall inputs; nevertheless, it will generate marked changes in the spatial pattern of sub‐canopy recharge in this forest landscape on the Oak Ridges Moraine. Copyright © 2015 John Wiley & Sons, Ltd.