Crown architecture and leaf traits of understory saplings of Macaranga semiglobosa in a tropical montane forest in Indonesia

Abstract Crown architecture and leaf traits were investigated in understory saplings (17–233 cm tall) of Macaranga semiglobosa in a tropical montane forest in Indonesia. The crown of a M. semiglobosa sapling consists of only leaves without branches. The total number of leaves per sapling increased from 4 to 19 leaves with an increase in trunk height in the examined saplings. Leaf area index (total sapling leaf area divided by crown projection area) increased with trunk height because of the increase in the total number of leaves per sapling with trunk height. Thus, it is suggested that there is limitation to avoid self‐shading. Leaf blade width was relatively constant from the top (the youngest leaf, leaf order 1) to the lowest (the oldest leaf) leaf. By contrast, petiole length increased from leaf order 1 to leaf order 6, and then remained relatively constant after leaf order 6. Vertical changes in the leaf mass per area within a crown showed a similar pattern to that of petiole length. Leaf nitrogen (a proxy of assimilation capacity) and chlorophyll (a proxy of light‐harvesting ability) contents per leaf area increased from leaf order 1 to leaf order 4, remained high until leaf order 7, and then decreased after leaf order 7. The present study suggests that petioles of M. semiglobosa elongate for longer than the leaf blades and that leaf morphological and physiological traits are coupled with the degree of petiole elongation occurring with vertical position, and this might increase light‐capture and nitrogen‐use efficiencies.