What factors are most influential in governing stemflow production from plantation-grown teak trees?

Stemflow (SF) has been recognized as an important process delivering water to spatially localized areas of the forest floor. Based on almost six years of daily SF data from nine teak trees in a Thai plantation, together with detailed above-canopy meteorological data and daily leaf area index (LAI) data, this study sought to better understand how specific biotic and abiotic factors affect both individual and stand-scale SF production from teak trees. Specifically, the factors affecting stemflow funneling ratio (SFFR) at individual and stand scales were analyzed and compared by means of boosted regression tree (BRT) analysis. The largest variation of SFFR among individual teak trees was observed in the leafed state. For trees taller than average, the BRT analysis revealed that vapor pressure deficit during rain was the most influential factor affecting SFFR. Vapor pressure deficit had a negative influence on SFFR, implying significant control of evaporative demand during rain. In contrast, for trees shorter than the average, rain duration (RD) was the most influential variable, having a positive correlation with SFFR. The stand-scale BRT analysis for all nine teak trees demonstrated that RD was the most influential factor affecting SFFR (exerting positive influence) but that an array of other factors (both abiotic and biotic) played intricate and complex roles in governing SFFR. The effect of LAI on SFFR was complicated and varied greatly among individual teak trees. It is possible that spatially heterogeneous flowpaths of intercepted water inside the teak canopy, which could be a product of the large-sized mature leaves of teak, may account for the tree-to-tree variation in the responses of SFFR to changing LAI. Although our study focused on teak trees, the demonstrated physically-based mechanistic explanations of stemflow production could apply to other even-aged deciduous forests and monospecific plantations.