• Forest growth models normally focus on the trees in the forest. Thus, these models allow
analysis if how the future forest structure will be modified by management, but they tell us little about other aspects of the ecosystem animal populations, hydrological functions, soil
conservation, and biodiversity. However, these aspects are more or less related to forest structure. Thus, several implications of timber harvesting on rain forest can be analyzed with
such models.
• FORMIX3 Huth et al., 1997, 1998 is a model for the simulation of the growth of tropical forest
stands with a size of 1 ha. To apply the model to a given forest stand, the user must provide stem number distributions for the different species groups. Tree species must be grouped into
functional groups according to their potential height and light demands. The model includes tree growth, mortality, regeneration, and competition as main processes.
2.3. Objectives of the Study :
• For investigating the long-term impact of different logging cycles the long-term changes in
forest structure due to logging, influence has the logging cycle on yield and structure of the remaining forest, useful are low impact logging methods compared to conventional methods,
the main differences concerning yield and forest structure using the FORMIX3 model.
III.
Methods
3.1. The site •
The Deramakot Forest Reserve is situated in Sabah North BorneoMalaysia, 5 25’N,
117 30’E appendix 1.
• Located just north of the equator, Deramakot has the perhumid climate typical of the inner
tropics. •
Mean annual temperature is 278 and mean annual rainfall is about 3500 mm. •
Geologically, Deramakot is characterized by tertiary sediments, mostly sandstone. •
The soils are mainly Acrisols. •
They are poor in nutrients and easily eroded, especially when the protective plant cover is removed.
• The Deramakot Forest Reserve is situated between 130 and 300 m in altitude.
• The prevailing forest type is Dipterocarp lowland forest.
• The forest remained essentially undisturbed until this century. Commercial logging started in
1956; intensity of logging and logging damages vary widely.
3.2. The rain forest growth model
• The FORMIX3 model was developed for the simulation of tropical rain forests in Malaysia
Huth et al., 1994, 1998. •
As main processes, the FORMIX3 model includes tree growth, competition, regeneration, and mortality.
In the following the author will explain the main parts of the model. A detailed description of all equations can be found in Huth et al. 1998 :
Rahmawaty : Technology Journal Report on Selection System-A Critique on Long term Impacts…, 2006
USU Repository © 2006
a. Species grouping and spatial structure
• Tropical forest stands are usually composed of a large number of species. For the purpose of
investigating forest dynamics, it is useful to classify species into a small number of functional groups.
• the author use three growth characteristics for grouping potential height, light demands for
growth and regeneration and derive five species groups for the Dipterocarp forest at Deramakot Table 1.
Table 1. Functional groups derived for simulation of growth of lowland Dipterocarp forest in Malaysia
a
• For simulation the forest stand area is divided into small patches. These patches have the size
typical of treefall-gaps as naturally created by dying large trees 20 m by 20 m. •
the author aim to describe the shifting stand mosaic, and we therefore simultaneously simulate several patches explicitly in their neighboring locations within the stand.
• The patches themselves are pictured as homogeneous and in each of the patches we adopt a
stratification of the tree community into height layers: All trees of a certain species group with their top falling into the range of a certain height layer completely belong to that layer a similar
approach was pursued with a gap model by Fulton, 1991, 1993.
• the author thus describe stand structure in the following way: tree species are aggregated into
five functional groups, the vertical structure of the canopy is separated into five height layers, and the heterogeneity across the stand area of 1 ha is represented by 25 patches of 20 m by
20 m.
b. Individual tree growth
