US-Republic of Congo (Brazzaville) Dissertation Enhancement: What Limits Recruitment of Tropical Trees? An Experimental Test of Seed and Establishment Limitation

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Ms. Connie J. Clark will conduct dissertation research in the Republic of the Congo under the supervision of Professor Douglas J. Levey of the University of Florida, and Professor Jean Marie Moutsabote of the Université Marien Ngouabi of Brazzaville, Republic of the Congo. Her research will consist of determining tropical tree diversity through recruitment limitation, using both the seed limitation hypothesis and the establishment limitation hypothesis.Intellectual Merit: Tropical forests account for nearly 50% of all known species. Yet, very little is understood about the processes that maintain or promote such diversity. Theoretical models suggest that processes limiting recruitment of new individuals into populations are key to maintaining species diversity. By keeping population numbers of more competitive species in check and slowing competitive exclusion, recruitment limitation should allow greater numbers of species to co-exist. The seed limitation hypothesis posits that the ability of a plant to recruit at a site is determined by the availability of seeds. It follows that at the community level the abundance and distribution of a species is determined by a "lottery" process -- recruits are drawn at random from the seeds that happen to arrive at a site. The establishment limitation hypothesis posits that recruitment is limited by the availability of suitable microsites for establishment. To experimentally test the relative importance of seed and establishment limitation, this project has established 30, 1-ha plots in logged and unlogged forests in the Republic of Congo, mapped and identified all trees and saplings, measured seed rain, and conducted seed addition experiments for six randomly-selected tree species in 90 subplots in all plots. Data are being gathered on seed predation, seedling emergence, seedling growth and survival, and several abiotic and biotic factors that likely influence the magnitude of seed and establishment limitation. The project is entering its third year and this award will support return trips to Congo to monitor the experiment and work with University collaborators to finalize species identification of seedlings, saplings and tree voucher specimens. Broader Impacts: Improved forest stewardship is being achieved through the project's collaboration with the Wildlife Conservation Society (WCS) and a major logging company, Congolaise Industrielle des Bois (CIB). WCS and CIB are working together to improve forestry and wildlife management in large logging concessions surrounding Nouabale Ndoki National Park, hoping to achieve Forest Stewardship Council (FSC) certification of 1.8 million hectares of contiguous forest by 2009. Another goal of the project is to improve the technical capacity of Congolese scientists and resource managers. In collaboration with the Royal Botanical Gardens (RBG), the project also provides an intensive field botany course for Congolese students (13 students trained to date). Voucher specimens collected during this study are being donated to the RBG to produce a field guide to the trees of Congo, which will provide an excellent resource to Congolese botanists.Because this project is being conducted in a high risk area for Ebola outbreaks, the co-PI has been trained as a "first responder" and participates in the WCS "field vet" program to monitor and control wildlife disease outbreaks in areas where multiple carcasses of primates are found. To assure humans in the concessions are armed with the information necessary to protect themselves and their families, participants in this project are part of an Ebola awareness campaign directed toward villagers most at risk of exposure to the virus.