Assessing the effects of a drought experiment on the reproductive phenology and ecophysiology of a wet tropical rainforest community

In this study we assessed the effects of an experimental drought on the reproductive phenology and ecophysiology of a rainforest tree community in the Wet Tropics of Queensland. We found that, although the drought increased fruiting activity in the community relative to the reference plot, species-level response was varied in both phenology and physiology. Climate change is expected to increase the intensity and occurrence of drought in tropical regions, potentially affecting the phenology and physiology of tree species. Phenological activity may respond to a drying and warming environment by advancing reproductive timing and/or diminishing the production of flowers and fruits. These changes have the potential to disrupt important ecological processes, with potentially wide-ranging effects on tropical forest function. Here, we analysed the monthly flowering and fruiting phenology of a tree community (337 individuals from 30 species) over 7 years in a lowland tropical rainforest in northeastern Australia and its response to a throughfall exclusion drought experiment (TFE) that was carried out from 2016 to 2018 (3 years), excluding approximately 30% of rainfall. We further examined the ecophysiological effects of the TFE on the elemental (C:N) and stable isotope (& delta;13C and & delta;15N) composition of leaves, and on the stable isotope composition (& delta;13C and & delta;18O) of stem wood of four tree species. At the community level, there was no detectable effect of the TFE on flowering activity overall, but there was a significant effect recorded on fruiting and varying responses from the selected species. The reproductive phenology and physiology of the four species examined in detail were largely resistant to impacts of the TFE treatment. One canopy species in the TFE significantly increased in fruiting and flowering activity, whereas one understory species decreased significantly in both. There was a significant interaction between the TFE treatment and season on leaf C:N for two species. Stable isotope responses were also variable among species, indicating species-specific responses to the TFE. Thus, we did not observe consistent patterns in physiological and phenological changes in the tree community within the 3 years of TFE treatment examined in this study.

Automated summary

This study assesses the effects of drought on the reproductive phenology and ecophysiology of a rainforest tree community. The results show that the drought had varied effects on species-level response in both phenology and physiology. This has implications for tropical forest function and highlights the potential impact of climate change on tree species.