Regional variation in the reproductive phenology of a tropical rainforest tree species, <i>Cardwellia sublimis</i>

Abstract Phenology is one of the most reliable tools for understanding the effect of climate change on forests. Although there has been increasing research into the effect of climate on phenological activity, little is known about how phenological patterns for the same species may vary among environments, particularly for tropical species. Here we analysed the reproductive phenology of an important tropical rainforest tree species in northeastern Australia, Cardwellia sublimis, and compared the patterns among seven different sites. We also tested and compared the climate drivers of reproductive phenological activity among sites for this species. Degree of seasonality varied across sites with most sites presenting moderate - high seasonality. Flowering and fruiting peaked in different seasons at the different sites and we found flowering and fruiting phenology were often influenced by different climate drivers at the different sites. Where the climate drivers were the same, the magnitude and direction of the effect of the drivers differed among sites. Precipitation was the most common climate driver of flowering, being significant for all sites, while fruiting was predominantly influenced by temperature and solar radiation. Finally, we found evidence that relationships between climate drivers and phenological patterns were dependent on inter-site differences in climate and geography. Our results demonstrate that species may present varied phenological patterns and varied responses to climate drivers dependent on environmental conditions and site location. These results have important implications for modelling phenological patterns based on limited field information, as well as for understanding species vulnerability to climate change.