The influence of canopy traits on throughfall and stemflow in five tropical trees growing in a Panamanian plantation

Tree canopies partition rainfall into temporary canopy storage, throughfall and stemflow. Knowledge of this partitioning process is needed to predict the hydrological effects of the large areas of tree plantations that are being established in the tropics. In this study, we compared throughfall, stemflow and interception in four Neotropical and one exotic tree species growing in selection trials in the Republic of Panama. We sought to answer four questions: (1) Are there interspecific differences in total throughfall and stemflow, and throughfall and stemflow for a range of rainfall depths?, (2) How do crown traits influence interspecific differences in throughfall?, (3) Does the spatial heterogeneity of throughfall differ among species? and (4) How do species affect litter biomass and other variables that influence rainfall erosivity? Rainfall depth mediated interspecific differences in throughfall and stemflow, the relative importance of crown traits in the interception process, and spatial heterogeneity of throughfall. Total throughfall was between 10.9 and 16.2% less in Acacia mangium than Gliricidia sepium, Guazuma ulmifolia, Ochroma pyramidale or Pachira quinata. Increasing rainfall also changed relative quantities of throughfall and stemflow among species. For example, throughfall was similar in Gliricidia and Acacia for small rain events, but increased more rapidly in Gliricidia with increasing rainfall depth. Interspecific differences in throughfall were driven, in part, by canopy traits. Leaf area index (LAI), crown depth and crown openness all affected throughfall from smaller storms, but live crown length was the only significant predictor of throughfall in storms that were deeper than 20 mm. The spatial heterogeneity of throughfall beneath individual tree canopies increased with rainfall depth, but was always lower in Gliricidia than in Acacia, Ochroma, or Pachira. High litter biomass and cover in Acacia and Ochroma relative to other species would be likely to buffer the erosive effects of raindrop impacts. These complex interactions between rainfall and species traits may affect local hydrology, and may need to be explicitly considered in reforestation projects in the seasonal tropics.