Print PageMany tropical forests experience one or more dry seasons annually. There is growing recognition that seasonal variation in water availability is a strong environmental force that shapes tropical plant species diversity, distribution, and functional biology. Research on tropical plant response to seasonal changes in water availability to date has focused on lowland ecosystems; however, there is a critical need for information on other ecosystems. In particular, regional modeling predicts that tropical montane regions are expected to experience greater rates of climate change in the coming years than tropical lowland regions, including dramatic increases in mean temperature and decreases in dry season precipitation. This information raises critical questions about the future of tropical montane forests.
In tropical pre-montane and montane forest around Monteverde, Costa Rica, we used an experimental dry down in a common garden and field-based observations to investigate the impact of water deficit on juvenile plant growth and physiology. We chose two low elevation species and two higher elevation species from the common plant genus Ocotea (Lauraceae), allowing us to control for the effects of evolutionary history and exploit the presence of a seasonality gradient that coincides with elevation.
Results/Conclusions
Despite a small decrease in soil water potential (0.2 MPa), plants subject to experimental dry down demonstrated significant decreases in leaf level water use, reducing stomatal conductance by up to 40% as compared to plants in a watered, control treatment. Additionally, plants in the experimental dry down demonstrated significant differences in morphology, including decreases in height and new leaf growth. Results were species-specific and no patterns emerged between low and higher elevation species. Results from the common garden experiment were similar in magnitude to physiological measurements made on juvenile plants in the field during the dry season.
Taken together, results from the common garden and field based observations suggest that changes in the frequency and magnitude of infrequent, dry season precipitation events are likely to have significant effects on the physiology and morphology of juvenile Ocotea spp. If these changes have a differential effect on species survival, then this will ultimately alter future tropical montane plant functional diversity and distribution.
