# Simulating Forest Dynamics of Lowland Rainforests in Eastern Madagascar
## 2 Materials and Methods
### The Forest Model FORMIND  
Though the framework of individual-based gap models is perhaps the best-suited model type to simulate rainforest dynamics [29; 30; 31; 32], few have been successful at achieving the persistence of the multitude of rarely occurring species, i.e., the immense biodiversity found in these forests, through space and time. The FORMIND model was developed specifically for the simulation of tree growth in tropical rainforests, by aggregation of tree species into plant functional types, and has been successfully applied to a larger number of sites [17].  
The spatial structure of the model is formulated in a similar manner to that of classical individual-based gap models [2; 3; 6; 30; 33]. As the dominant driving factor of forest growth dynamics, competition for light and space occurs among the individual trees. Primarily, it is light climate that strongly influences the process of growth and also establishment; space competition is realized by the process of thinning, undergone when individuals die due to resource limitations brought on by crowding. Trees are simulated individually and each simulated tree belongs to a certain plot. Horizontally, the model sub-divides the one-hectare plot into 20 m \(\times\) 20 m subplots, a size which roughly corresponds to the canopy spread of a mature canopy dominant tree [3; 11]. In this way, all trees in one sample plot compete for light and space both vertically and horizontally. In addition, gaps formed by the death of a dominant tree can disrupt and influence growth in both the subplot where the gap formed, as well as adjacent subplots (see: [11]).  
The model is driven by the main processes of tree growth, competition for light and space, mortality, and regeneration. When a tree falls and a canopy gap is created, the vertical leaf distribution and light availability are calculated at the tree level. Biomass growth, also calculated at the tree level, is calculated as a balance of carbon based on photosynthesis, respiration, biomass allocation, and litter fall. Photosynthetic production is calculated as a function of the local available light (according to light response curves).  
The basic structural framework of FORMIND follows the growth of individual trees while maintaining an overall balance of forest carbon on multiple levels. Forest growth in general is constrained by the photo-production of leaves, light climate within the different canopy layers, and loss of biomass through thinning or senescence. Competition among individual trees occurs for both light and space. As is a basic tenet of individual-based gap models, canopy gap formation caused by tree falls drives age, species, and canopy heterogeneity across the forest mosaic [33]. A full listing of the equations that drive growth, photosynthesis, mortality, recruitment, and distribution dynamics in FORMIND can be found in [PERSON] et al. [17]. Due to the individual- and process-based approach in FORMIND, it is possible to estimate forest stand productivity and respiration. Integrating carbon stocks for the deadwood and for the soil, FORMIND has the capability to simulate the full carbon balance of a forest stand [18; 34; 35; 36]. In order to simulate the total ecosystem carbon balance, above- and belowground carbon stocks and the resulting net ecosystem exchange (NEE in tonnes C per ha per year) are calculated as the balance of carbon sequestration and carbon emissions (see [17; 35] for a detailed description of the module).