INTRODUCTION

There is growing evidence that changes in climate are altering the ecology of tropical forest plant communities around the world. In Western Amazonia, contrary to the more frequent and severe droughts predicted in Eastern and Central Amazonia, climate models predict (along with increasing temperatures) an increase in mean annual rainfall and more prolonged wet periods, which would typically lead to increased cloud cover and so a decrease in solar irradiance. This decrease in available energy may in turn affect species’ fitness through flowering success, as previous evidence has suggested that plant species synchronize their flowering with periods of peak of irradiance.

OBJECTIVES & METHODS

Here, we examine how the mean monthly values of six climate variables (irradiance, rainfall, relative air humidity, and minimum, average and maximum air temperature) have changed over a 19-year period (2000-2018) in a 25-ha ever-wet tropical forest plot in Western Amazonia. We analyzed how the inter-annual fluctuations in these variables have influenced flower and fruit production among 248 plant species (recorded in 435 phenology traps), and how species response differs across different guilds (canopy vs. understory trees, climbers, epiphytes) and according to their resource-use traits (wood density, SLA) and dispersal syndrome.

RESULTS

We found an increase in mean annual air temperatures during the study period, especially in minimum temperature, for which mean annual values varied from 20.8°C to 22.6°C and 45% of the warmest years occurred after 2009. In contrast, mean annual irradiance dropped by ca 10%, with 40% of the lowest-irradiance years occurring after 2009. Mean annual rainfall and relative humidity did not show any clear trend through this period. Nearly 65% of the species responded negatively in terms of flower production to both increasing temperature and decreasing irradiance, even after controlling for the effects of all the other climate variables, which in turn reduced fruit production. The strength and modality (positive or negative association) of species’ responses were not associated with any particular trait, guild, or family.

CONCLUSION

Our results suggest a negative impact of increasing temperature on flower and fruit production, potentially mediated by higher respiration costs, along with a decrease in the availability of solar energy. These findings provide important insights to better predict shifts in species composition in responses to climate changes in ever-wet forests, which have been poorly investigated so far compared to more seasonal tropical forests.