The distribution of rainwater by the forest canopy into stemflow, throughfall, and interception is determined by tree species characteristics (canopy storage capacity, bark roughness, bark water storage, and bark thickness) as well as canopy position (midstory vs. overstory). In upland oak ecosystems, which are undergoing a compositional shift from shade-intolerant, fire-tolerant oaks to shade-tolerant, fire-sensitive species (i.e., mesophytes), canopy water partitioning between species may have broad implications for water availability and forest flammability. To assess interspecific differences, we measured canopy and bark characteristics on 5 different species of overstory and midstory trees (Quercus alba, Quercus falcata, Quercus coccinea, Acer rubrum, Ulmus alata, Carya tomentosa, Carya glabra var. glabra). At approximately monthly intervals beginning in November 2017, we measured throughfall volume, stemflow depth, and soil moisture at three sections per tree, (bole, mid canopy, edge of canopy) and three depths 7.6 cm, 12 cm, and 20 cm, to determine how canopy water inputs impacted soil moisture availability. We will also determine how bark characteristics including roughness, thickness, and water storage capacity interact with the storm event and affect the amount of stemflow that reaches the base of the tree.
Results/Conclusions
Mean monthly stemflow flux from overstory trees was 4.3 times larger in hickory and 4.0 times larger in red maple compared to white oak (p < 0.001 and p = 0.014, respectively). However, there were no significant differences observed in throughfall beneath tree canopies (overstory: p = 0.607; midstory: p = 0.800). Soil moisture was significantly higher beneath red maple overstory trees (Volumetric Water Content = 0.315) compared to southern red oak (VWC = 0.242, p = 0.012) and white oak (VWC = 0.243, p = 0.014). Soil moisture was also beneath midstory trees as a function of species (p < 0.001), although the specific mesophtye vs. oak relationship was not clear. Differences in canopy water partitioning, even during leafless canopy conditions, are evident between mesophyte and oak species. These results suggest that structural differences in tree crowns and bark morphology are important traits determining water inputs to the forest floor. Future work will explore how these relationships change when leaves are present in the canopy and how prescribed fire impacts canopy structure.