Phenology of 50 tree species across 9 years in a South Asian tropical rainforest indicates complex influence of climate, traits, and phylogeny

In relatively aseasonal tropical rainforests, few studies have explored long-term phenological patterns of a high diversity of tree species in relation to climate, phylogeny, and functional traits. In these systems, short-duration seasonal pulses of irradiance and water deficit are expected to provide narrower windows for leafing and flowering and wider windows for fruiting across prolonged wet seasons, potentially mediated by functional traits and phylogenetic relatedness. Here, we document leafing, flowering, and fruiting phenology of 50 tree species (920 – 1077 trees, 10 – 42 trees/species) monitored monthly over an 9-y period (2017 – 26) in a relatively aseasonal south Asian tropical rainforest in the Anamalai Hills, Western Ghats, India. We examined correlations between climatic variables (irradiance, daylength, temperature, precipitation) and tree phenology and Mantel correlations among similarity in monthly phenology, functional traits (wood density, seed size, and maximum height), and phylogenetic relatedness. We then investigated the phylogenetic signal of phenological traits (frequency, amplitude, duration, and peak month) using Pagel’s λ. Leaf flushing and flowering showed distinct seasonality and negative associations with daylength and precipitation, whereas fruiting showed greater temporal spread and weaker associations with climate. Functional traits or phylogeny did not significantly influence leaf flushing and flowering, whereas dissimilarity in fruiting was correlated with phylogenetic distance and peak fruiting month showed a significant phylogenetic signal (λ = 0.96). The results indicate that in relatively aseasonal tropical rainforests, proximate climatic cues more strongly influence leaf flushing and flowering, whereas phylogenetic constraints affect timing of fruiting and may cause lineage-specific vulnerabilities to climate change.