Changes in Community Composition and Functional Traits After Cyclones and Fire in a Pacific Rainforest

International audience

anglais. Tropical cyclones are common disturbances on many Pacific islands and affect forest structure and community composition. However, we know little about the process of succession after disturbances in the tropical South Pacific. We utilize published data of vegetation surveys in a lowland tropical rainforest reserve in Samoa that were undertaken within 1 year, and after 6 and 15 years, after two cyclones and a fire that occurred in 1990 and 1991. We combine these surveys with functional trait data from literature and the field. Community and functional composition differed little from inferred pre-cyclone conditions soon after the disturbances but had changed considerably 6 years after the disturbance. Early successional species with functional trait characteristics relating to resources acquisition and faster growth (lower wood density, larger leaf area, shorter maximum height, smaller seeds) had become dominant 6 years after the disturbances, but had declined considerably by 15 years. No clear differences in community-weighted means of functional traits were detected between burned and unburned forest, but community composition differed considerably. In particular, the introduced rubber tree, Funtumia elastica, which was functionally intermediate between early and late successional species, had become very abundant in burned forest. Our results suggest that ecological functions may be more resilient to cyclone disturbance than community composition, but this requires further study. Our findings highlight the impact of cyclones on community composition and functioning, the importance of long-term data for investigating the recovery after disturbances, and the potential of multiple disturbances to facilitate the proliferation of invasive species.