Interactive effects of functional traits and rainfall event size on stemflow in a tropical montane cloud forest

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Abstract This study analyses how rainfall (P) event size influences the effect of functional traits on stemflow volume of woody plants in a tropical montane cloud forest. In addition, it was investigated whether multiple regression models based on functional traits provide better predictions of stemflow volume than allometric equations using only basal area (BA). Eighteen functional traits of size, structure, bark and leaf of woody plants in the overstory, midstory and understory were analysed. Stemflow volume was determined to a greater extent by size traits, mainly basal area and crown area, with these relationships becoming stronger as P event size increased. Stemflow volume was also influenced by other traits that affect the efficiency with which individuals produced stemflow. The crown area/basal area ratio showed the strongest correlation with the stemflow production efficiency metrics (funnelling ratio and stemflow proportion). Bark traits had a negative effect on funnelling ratio and stemflow proportion, with a tendency to be stronger in smaller P events, while vascular epiphyte cover showed the opposite trend. Multiple regression models with two to three variables explained 43 to 81% of stemflow volume variation, depending on P event size. For P events <15 mm, the fit was generally better for multiple regression models than for basal area models, while for P events >15 mm, differences among models were small. Functional traits largely define stemflow at the level of individual plants, but this relationship is mediated by P event size.

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