COS 50-2 - Decreasing flower production coincides with warmer and more humid atmospheric conditions in a Western Amazonian forest

Abstract: There is growing evidence that climate change is altering the ecology of tropical forest tree communities around the world. Although these effects are global, they are of particular importance in the forests of Amazonia because of the area’s outstanding biodiversity and crucial role in the global carbon cycle. Climate models predict that everwet Western Amazonian forests will face warmer and wetter atmospheric conditions, along with increased cloud cover causing reduced solar irradiance. Examining how these changes may affect plant species reproduction is crucial, as species regeneration and whole forest productivity and dynamics, as well as the nature and quantity of food sources for higher trophic levels, in large part depend on the successful production of flowers and fruits. Here, we tested whether inter-annual variation in flower production for 184 species of trees, shrubs, and climbers, has changed in response to fluctuations in solar irradiance, rainfall, temperature, and relative humidity over 18 years (2000-2018) in an everwet tropical forest in Ecuador.

Over the study period, community-level flower production showed an overall declining trend. In parallel, we observed a marked increase in temperature and relative humidity, especially at night, along with a decrease in solar irradiance. Using regression models while controlling for temporal autocorrelation biases, we showed that flower production was best explained by, and negatively associated with night-time temperature and relative humidity. Species responses varied widely but did not differ among guilds or lineages.

Our results suggest that warmer nights and greater atmospheric water saturation may have negatively impacted tree species’ reproduction over the years, potentially via alterations of the metabolic and/or cue-based processes associated with flowering. If these trends continue, the reproductive output of the forests of this Amazonian region may lead to lower potential for their regeneration as well as reduced fruit resources for animals and humans that depend on these forests for food and alter tree regeneration dynamics. This study sheds light on how plant communities will respond to climatic changes in this everwet region, which has been poorly investigated compared to more seasonal areas of the Amazon.