TY - JOUR T1 - Celestially determined annual seasonality of equatorial tropical rain forests JF - bioRxiv DO - 10.1101/454058 SP - 454058 AU - Kanehiro Kitayama AU - Masayuki Ushio AU - Shin-ichiro Aiba Y1 - 2018/01/01 UR - http://biorxiv.org/content/early/2018/10/31/454058.abstract N2 - Annual vegetative periodicity is not well known in equatorial tropical rain forests except for photoperiodically induced or El-Niño-drought induced synchronous flowering/fruiting. The lack of vegetative periodicity such as leaf flush and fall in these forests has been believed to reflect an “aseasonal” climate. In the present study, we show a distinct annual seasonality in canopy dynamics using a Fourier analysis with a statistical significance test on the long-term, fortnightly monitored dataset of leaf litterfall in nine Bornean evergreen tropical rain forests on Mount Kinabalu. Such periodicity occurs across altitudes and soil types in all years irrespective of the year-to-year climatic variability, suggesting that regional climatic factors rather than local edaphic and/or biotic conditions cause the precise 1-year periodicity. We examine climatic factors that have causative effects on the distinct 1-year periodicity using a newly developed spectrum convergent cross mapping analysis that can distinguish causal relationships from seasonality-driven synchronization. We find that mean daily air temperature is most strongly, causatively related to the 1-year periodicity of leaf litterfall. We suggest that annual temperature changes in association with the movement of the intertropical convergence zone cause the distinct annual vegetative periodicity. Because vegetative periodicity can be transmitted to the dynamics of higher trophic levels through a trophic cascade, interactions between vegetative periodicity and daily air temperature, not rainfall, would more strongly cause changes in the dynamics of forest ecosystems. Our results show that we need to redefine our concept of equatorial “aseasonal” tropical rain forests, and that air temperature is a more important factor than other climate variables in the climate-forest ecosystem interaction. ER -