Plants have evolved mechanisms to track seasonal environmental variation, enabling them to time key life-history events to appropriate seasons. While the proximate cues for flowering initiation are well documented in the temperate areas, it is still unclear what the flowering cues are in the tropics, especially in subtropical regions.
In this study, we would like to identify the species-specific proximate cues that initiate flowering in a subtropical rain forest using a 19-year phenological data from the Fushan Forest Dynamics Plot, Taiwan.
By analyzing 30,800 flower records of 16 species in the Fushan forest, we parameterized phenology models with daily meteorological data. We compared first flowering dates (FFD) predicted by eight possible proximate cues involving photoperiod, solar irradiance, temperature, and rainfall.
We found considerable interannual variation in the median FFD for most of the study species, ranging from 21 to 101 days. The early-flowering species tended to have greater interannual variation in FFD than the late-flowering species. For 14 out of 16 study species, proximate cues concerning temporal variation in temperature well explained the interannual variation in FFD. The early-flowering species, like Machilus and Castanopsis spp., might be cued by one to three months of low temperature in the previous fall or winter. In contrast, the late-flowering species might flower after two to four months of consistently warm temperature. The proximate cue concerning irradiance also explained interannual variation in FFD for 11 species but with higher prediction errors than temperature-related cues. The hypothesis related to seasonal variation in rainfall failed to predict the timing of flowering in any species.
Our results suggest that future changes in temperature might alter flowering times for most species in subtropical forests, which could lead to changes in ecosystem processes and biosphere feedback to the climate systems.