FORMIX3: a forest model to simulate tree growth in the tropics

Ecosystem structures of tropical forests are under threat due to changes in climate and land-use. There is increasing evidence that many logging strategies are not sustainable since they exceed their regeneration capacities. The need for a reliable assessment of rainforest’s growth dynamics, over long-terms and under changing environmental conditions, had led to the development of the dynamic forest growth simulation model FORMIX3. This model enables us to investigate the effects of both different logging methods and climate change on the rainforest’s succession.

Animation of the forest model FORMIX3. Trees are colored according to their functional group.

Animation of the forest model FORMIX3. Trees are colored according to their functional group.

To simulate the very high number of tree species in tropical rainforests is particularly challenging. Therefore, tree species are aggregated into few functional groups in FORMIX3, according to their physiognomical and physiological demands. The model describes individual tree growth on the basis of a carbon balance, taking various processes into consideration: tree growth is constrained by  photoproduction of the leaves due to the light climate in different canopy layers and locations within the forest stand, and by biomass consumption and losses. The trees compete for light and space. Dying large trees fall down and form gaps in the surrounding forest. Jung trees germinate when the light climate on the forest ground is suitable.

The model was applied to investigate long-term impacts of various logging strategies and climate change in different types of tropical rainforests, e.g. in Paraguay and Malaysia (dipterocarp forest of the lowlands in Sabah, hill dipterocarp forest in Sarawak, peat swamp forest in Malaysia Peninsula). A complete model documentation, results of comprehensive model testing and an exemplary model application as well as discussions of simulation results are available in Huth et al. (1998, 2000, and 2001).