Assessing plant species responses to water availability is critical for understanding community assembly and for predicting how species composition and diversity will shift in response to climate change. In particular, species’ ability to withstand drought likely plays a key role in determining species responses to current and future climate. Drought resistance has been shown to vary widely among tree species in seasonal tropical forests and to shape spatial patterns of seedling dynamics and species distributions across moisture gradients. We predicted that species' drought resistance also influences temporal variation in seedling dynamics, with drought sensitive species showing stronger year-to-year variation in performance related to climate. In contrast, temporal variation in seedling performance of drought resistance species is expected to be lower and/or less strongly linked to climate variation. We test these predictions using data from a 15 year study of seedling dynamics on Barro Colorado Island (BCI, Panama), coupled with experimentally-measured data on species drought resistance for tree species at the site. Specifically, we censused seedlings >=20 cm tall and <1 cm dbh (diameter at 1.3 m) in 20,000 1x1 m2 seedling plots located at 5-m intervals throughout the BCI 50-ha Forest Dynamics Plot every 1-2 years since 2001.
Results/Conclusions
Our long-term study has generated data on recruitment, growth and survival of >100,000 seedlings of >300 species. These data reveal large year-to-year variation in tropical tree seedlings dynamics at both the community and species levels. Both total annual rainfall and dry season severity varied over time and significantly influenced seedling performance. Species drought resistance had a significant impact on species responses to water availability, influencing both spatial and temporal variation in mortality. Overall, our results demonstrate the importance of water availability in shaping the dynamics of tropical forest regeneration. This suggests that significant shifts in species composition and diversity may occur as a result of shifts in precipitation patterns due to anthropogenic climate change.