The diversity of tropical rain forest tree species is aggregated in a few, typically five, species groups. Each species group has its own growth process characteristics and its own typical mature height. For each species group the model calculates biomass and tree number in five distinct canopy layers.
Although light parameters and light conditions differ in each layer, the processes in each layer are structurally identical: photoproduction, respiration, shading of lower layers, transitions of trees from lower to higher layers. Photoproduction and respiration rates lead to biomass, diameter, height, and leaf mass growth in each layer. The insolation into a layer, and the leaf mass of trees within the layer determine p hotoproduction of these trees and light conditions in lower layers (competition for light). Mortality of trees is included in the model as random event (including competition for crown space). Large dying trees can fall down and create gaps in the forest. Production of seeds is assumed to produce a constant seed bank and assure continuous seedling establishment.
These concepts are used to model the growth of rain forest in patches of size 20 m by 20 m. Normally a 1 ha stand composed of 25 patches is simulated.
At present, model structure restricts application to evergreen rainforests at sites where no droughts are to be considered and constant climatic conditions throughout the year can be assumed. The development of a site module accounting for soil properties and topography is in progress.
The model was applied to investigate the long-term impact of different logging strategies in different formations of tropical rainforest in Malaysia: mixed dipterocarp forest (MDF) of the lowlands in Sabah, hill MDF in Sarawak and peat swamp forest in Malaysia Peninsula. Complete model documentation, results of comprehensive model testing and an exemplary model application in Sabah including the discussion of simulation results are available (Huth et al. 1996).
Huth, A., B. Hahn-Schilling and H. Bossel, 1994
Untersuchung der Auswirkungen von verschiedenen Nutzungsstrategien auf das Wachstum von Moorregenwald - Simulationen mit FORMIX. Zeitschrift für Ökologie und Naturschutz 3: 217-225.
Bossel, H. and H. Krieger, 1994
Simulation of multi-species tropical forest dynamics using a vertically and horizontally structured model. Forest Ecology and Management 69: 124-144.
Bossel, H. and H. Krieger, 1991
Simulation model of natural tropical forest dynamics. Ecological Modelling 59: 37-71.