Stemflow hydrology and DOM flux in relation to tree size and rainfall event characteristics

Numerous studies have examined the variability of stemflow across different tree species under different meteorological conditions. However, studies have rarely considered stemflow associated with individual rainfall events and stemflow DOM flux. Therefore, we collected stemflow data from >100 individual rainfall events across four diameter size classes (20–30 cm, 30–40 cm, 40–50 cm, and DBH > 50 cm) of Castanopsis cuspidata in an evergreen forest (35° 26′ N, 136° 47E). The main objectives were to evaluate the stemflow hydrology and DOM flux characteristics in relation to tree size and different rainfall intensities based on a large dataset of individual rainfall events. In line with previous studies, the mean stemflow volumes and percentages of larger trees were higher than those of smaller trees; smaller trees have a higher funneling ratio than larger trees at both tree-scale (FR_t) and stand-scale (FR_s), which means that smaller trees are more effective in funneling water to their base. However, tree size significantly affects the stemflow volume and percentage only when the rainfall intensity is below 15 mm h⁻¹. Tree size had a limited effect on the stemflow DOM concentration and stemflow DOM yield at a monthly scale. However, stemflow DOM flux and the flux-based DOM enrichment ratio were affected profoundly by tree size. Similar to the funneling ratio, small trees had a higher flux-based DOM enrichment ratio and supplied more DOM per unit trunk basal area. Thus, in addition to tree species, we suggest that tree size is also an important factor influencing the heterogeneity of the spatial patterns of the soil solution chemistry near the tree trunks.