Complex interactions between diversity, land use and carbon stocks in tropical landscapes

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Tropical forests occupy 12% of the terrestrial surface, harbour more than half of terrestrial diversity and hold over 40% of terrestrial carbon (C). These forests are highly threatened globally and deforestation in the tropics accounts for some 10% of total greenhouse gas emissions. This Discovery grant proposal therefore seeks to advance scientific knowledge of the C sequestration potential of tropical landscapes. Building on my interests in global change biology, more specifically, in the interactions between land use, tree diversity and C storage, my long-term objectives for this research program are (1) to further the understanding of the functional relationship between biodiversity and ecosystem function in tropical forests, and (2) to evaluate the synergies/tradeoffs between diversity and C stocks conservation at the landscape level. To meet my objectives I propose combining three different approaches. First, ecologists have invested substantial efforts over the past two decades to document and identify mechanisms explaining the relationship between biodiversity and ecosystem functioning. Several review papers and meta-analyses now provide evidence that community-level performance of species mixtures tends to be higher than the average of their monoculture counterparts. Forested ecosystems however have been under-represented in this research effort to date. To address this gap, I established, in 2001, an experimental planted forest in Sardinilla, central Panama, which brought the study of relationship between biodiversity and ecosystem function to a new level of realism. With > 5000 trees, this planted forest is one of the oldest experimental sites studying the intricate links between tree diversity and C cycling. In the coming five years of this research program, I propose to use the long term data set from the Sardinilla planted forest to further the understanding of the mechanisms underlying the biodiversity-ecosystem function relationship. Relying on modeling, I will also evaluate the importance of tree diversity for the stability of ecosystem functions. Another part of my proposed research activities builds on our work on the sources of uncertainties plaguing the estimates of tropical forest C stocks. Our results suggest that the dynamics of forest regrowth and its impact on C stocks is a major source of uncertainty. Accurate estimates of C in secondary forests demand exceedingly intensive sampling because accumulation rates depend upon both forests and intervention types and ages, I therefore propose to create a database compiling existing data on secondary forests biomass in Panama and generate new data to fill existing gaps. The data base will serve to estimate the rate of accumulation of forest biomass and C through time for different forest types. This chronosequence of succession will be informed by past land use. The database will be first developed for Panama, but I hope that it will grow to include data from the entire Latin American region. Finally, I hope to advance the understanding of complex mosaics of vegetation types with regard to biodiversity and C conservation. Work that we recently carried out at small-spatial scales in Panama suggests that there might be a tradeoff, mediated by density, between tree diversity and forest biomass. Here I propose to work in eastern Panama in close collaboration with local indigenous and colonist farmers to develop a baseline for C and biodiversity at the level of an entire watershed disentangling the effects of land use history and biodiversity on C stocks. Modeling will provide information on the consequences of alternative future land uses making a solid contribution to the study of social-ecological systems.