Resistance and recovery of seedling communities to drought in Borneo: examining growth-dieback trade-offs

Background/Question/Methods

Climate change induced alterations to global precipitation patterns are having substantial effects on tropical forests. These shifts in precipitation patterns are characterized by more extreme rainfall events, increased variability in rainfall patterns and more frequent and severe droughts driven by an intensification of El Niño Southern Oscillation events. The effect of altered precipitation patterns on species coexistence is dependent both on species resistance to water stress and recovery following that stress. Under this concept, I hypothesize a trade-off in which fast growth rates under high water availability come at the cost of poor competitive ability for water. Faster growing species would be competitively dominant under wet conditions when water is not a limiting resource but would decrease in fitness under drought conditions. Therefore, the impact of drought on community dynamics must take into account direct dieback from drought as well as pre- and post-drought growth rates. I tested resistance to and recovery of seedling communities in Borneo from drought using paired-plots of natural rainfall and rainfall exclusion. Dieback and growth were assessed based on direct measures of leaf area.

Results/Conclusions

Species rank in leaf area was different between control and rainfall exclusion plots both immediately following the drought as well as 4 months later. Furthermore, a trend indicating a trade-off in growth rate under wet conditions and dieback was found, although it was not significant. However, a significant relationship was found among species between dieback during drought and recovery of leaf area after drought. This result supports the hypothesis that drought tolerant species have the benefit of improved survival during drought as well as faster recovery from drought. Overall these results are consistent with the theory that short-term alterations to water availability in Borneo can act as a stabilizing mechanism promoting spatial and temporal coexistence. There are obvious limitations to this mechanism, as persistent and severe droughts will lead to alterations in nutrient dynamics, increased forest mortality and potentially species extinctions.