| 要旨トップ | 目次 | | 日本生態学会第73回全国大会 (2026年3月、京都) 講演要旨 ESJ73 Abstract

一般講演（ポスター発表） P1-267 （Poster presentation）

#### Leaf demography and functional traits of deciduous and evergreen trees in a seasonally dry tropical forest in northwestern Madagascar【A】【E】

*Seiya SUNAYAMA（Kyoto Univ.）, Ayuki OKAMOTO（Kyoto Univ.）, Yutaro FUJIMOTO（Kyoto Univ., FFPRI）, Kaoru KITAJIMA（Kyoto Univ.）

Adaptive strategies of trees in seasonal environments are often categorized into two leaf habits: deciduous and evergreen. However, unlike in temperate forests, trees in seasonally dry tropical forests exhibit continuous variation in leaf fall during the dry season, with some trees shedding all their leaves at the onset of the dry season and others shedding leaves progressively until the end of the dry season. This study aims to test the hypothesis that greater leaf fall during the dry season is associated with higher stomatal conductance, which allows greater photosynthetic carbon gain but also higher water loss, whereas lower leaf loss is associated with higher leaf mass per area (LMA) and leaf dry matter content (LDMC), which confer greater toughness on leaves. At the edge of a 4-m-wide trail, 20 tree species retaining leaves in July 2025 were selected to monitor the degree of leaf loss and seasonal changes in stomatal conductance (3–20 current-year shoots from 3–5 individuals per species). Leaf fall rate was calculated as the ratio of leaf number in October or November to that in July. Stomatal conductance of adjacent leaves was measured with a leaf porometer (LI-600). LMA and LDMC were determined in July and October for each species. The degree of leaf loss varied continuously among species; by November, about half of the species had gradually dropped more than 20% of their leaves, with some individuals losing all their leaves, while other species showed little change in leaf number. Stomatal conductance also showed high interspecific variation (0–0.5 mol m-2 s-1), reaching almost zero in about half of the species with a low leaf fall rate. As hypothesized, leaf fall rate was significantly positively correlated with stomatal conductance but showed no significant correlation with LMA and LDMC. Five species showed leaf flushing at the same time as leaf fall during the dry season. This leaf exchange may contribute to continuing photosynthesis in species with a short leaf lifespan. These results highlight the importance of considering the degree of dry-season leaf retention as a continuous variable rather than treating leaf habits as a dichotomy between deciduous and evergreen. Such consideration may clarify how diverse species with various physiological and morphological traits are adapted to the prolonged dry season.

日本生態学会