# Simulating Forest Dynamics of Lowland Rainforests in Eastern Madagascar
## 1 Introduction  
Ecological modeling has proven to be an effective approach toward understanding key factors that influence or control the long-term behavior of a system of interest. Among these, the individual-based gap models (IBGMs) have a long history of successful forest simulation across temperate and northern forests (See: [1] for recent review). Establishment, diameter growth, and mortality of trees are usually simulated on an annual time-step, within a plot of a defined size. As a defining characteristic of IBGMs, the life history of each individual is simulated as a unique entity with respect to these processes [2; 3; 4]. For each individual, simple interaction rules (e.g., shading, competition for limiting resources, etc.) in conjunction with rules for birth, death, and growth are the basis for individual response functions, which are driven by the formation of canopy gaps that occur when a mature tree falls [1; 2; 3; 5]. However, to formulate such rules, detailed information on the dynamics of individual tree species (growth rates, establishment requirements, height/diameter relations) is required. Several individual-based models (IBGMs) including FORMIND, which was applied in this study, have been successfully adapted to understand patterns of growth and competition in forests worldwide. Other examples of IBGM study sites lie in the subtropics or in mountains, including Australian montane rain forests [6] and a subtropical rain forest in Southern Africa [7]. Often, these models have been developed in relatively well-studied sites. For example, [PERSON] [8] implemented an individual-based gap model with 34 different species and tested it on its ability to reproduce species abundance-diversity curves in response to hurricane disturbance in the montane rain forest of the Luquillo research site in Puerto Rico. [PERSON] et al. [9] inspected the changes in these diversity curves across a theoretical spectrum of disturbance using a three-dimensional version of [PERSON]'s model. Independently and working on the same site, [PERSON] et al. [10] implemented an 11-species version of a similar individual-based model and also inspected the impact of different ecological disturbances. These model examples capture inherent difficulties that exist in the development of rainforest-specific modeling frameworks. For instance, researchers must decide whether to represent the Luquillo forests as an assemblage of 34 species or of 11 species. The decision highlights the tradeoff that exists between the difficulty in estimating performance parameters across individual species (presumably the motivation for reducing the number of species) and the degree to which diversity is an important consideration in the ecosystem response. Since these models simulate the dynamics of changes in the state of individual trees, the number of species has little effect on the computer processing demands of IBGMs simulating forests with differing species richness. A recent application individual-based modeling has been a framework to study and project ecosystem productivity and carbon flux through time for a given forest. An advantage of utilizing this type of modeling framework is that the mechanics that drive these fluxes (i.e., growth, biomass allocation, competition, mortality), can be measured and studied at the individual tree level. The application of this model type gives the user the flexibility to distinguish patterns and processes at multiple spatial and temporal scales [11; 12; 13]. Most ecological modelers realize that there is a balance between model simplicity and model complexity and hope that there is some sort of \"sweet-spot\" between the two poles, the so-called Medawar zone (see [14]). However, differences in approach have thus far precluded the universal acceptance of any one modeling approach as the most appropriate choice for forest ecologists working in the tropics.