Exploring the mechanisms of monodominance in species-rich tropical forests using process-based simulation models and percolation theory

• Applicant: Dr. Jürgen Groeneveld
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems ; Forestry
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 383679788

Tropical rainforests show extreme high species diversity but sometimes include large areas dominated by just one tree species. This surprising phenomenon has been referred to as monodominance whenever more than 60% of all canopy trees are from one species. Usually edaphic factors alone cannot explain the emergence of such monodominant areas. Several mechanisms have been described which could explain monodominance, for example local dispersal of large and therefore strong seeds, but so far no comprehensive theory of monodominance exists.In particular, so far no mechanistic model exists that would allow us to explore the relative importance of all known monodominance mechanisms. We will close this gap by developing a modular, spatially explicit simulation model. Processes and structures relevant for the model will be based on literature, discussed with field experts, and underpinned with data from existing trait databases, such as sPlot and TRY. In addition to mechanisms discussed so far, we will also explore the role of increasing defaunation, which has been reported for many rainforests and could lead to increasingly local and thus clumped seed dispersal and, hence, monodominance.Model validation will be based on independent predictions, including established principles from systems science. The coexistence of species-rich and monodominant forest structures corresponds to a so-called critical point. In a pilot model study we were able to show that this coexistence is only possible for a narrow range of model parameters. Percolation theory will be used to explore this parameter range and deduce general, testable system properties. For example, since our simulations take place on grids of finite size, methods of finite size scaling from statistical mechanics will be used.The applicant and co-PIs of the project have already established an interdisciplinary network of leading scientists who are working on monodominance, forest modelling and simulation-based theoretical physics. Members of this network will meet in two workshops in Leipzig in 2017 and 2018, to synthesise their knowledge about monodominance and discuss suitable empirical and theoretical methods for quantitative analyses of monodominance.The combination of the systems theory and ecological perspective will put our findings in a larger context and thereby help to understand how both species-rich and species-poor forests emerge and coexist, and how anthropogenic factors affect forest structure. This project will thus significantly improve our understanding of processes that generate, stabilize, or erode biodiversity.

• DFG Programme: Research Grants