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
• The model calculates the development of a forest stand based on collectives of trees, which
each Includes the trees of one species group in a certain height layer of a single patch. •
Such a collective is characterized by the number of trees included and by the size of one representative tree.
• Using tree geometry relations, the size of a tree can equivalently be expressed in terms of its
above-ground biomass B, height h, or diameter d diameter at breast height, respectively Bossel and Krieger, 1991, 1994; Schafer et al., 1992:
• The crown projection area is calculated from stem diameter d via the proportionality of stem
diameter and crown diameter UNESCO et al., 1978; Whitmore, 1984; Poker, 1993. Assuming G = wood density,
F = form factor TR = stem biomass
f ti
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a fixed leaf area index LAI within crowns, the trees leaf area LT follows from its crown projection area.
• The growth of the individual tree is based on the carbon balance.
• The carbon balance includes photo production P of the tree on the one hand and biomass
losses due to respiration and renewal on the other hand Bossel and Krieger, 1991, 1994:
• Photo production P of a tree is calculated from the trees leaf area LT and its specific
productivity: B = above-ground biomass of tree
SR = biomass loss rate
h = height to the base
h
1
= to the top of the crown •
The specific productivity of the leaves at height h depends on the local irradiance Ih inside the canopy.
• The dependence of specific photosynthetic productivity on irradiance is modeled using a
Michaelis-Menten-type light response curve parameterized for each species group M initial slope of light response curve, PMAX maximum photosynthetic production.
• Within the patch, light attenuation downwards in the canopy is calculated with respect to
absorption by the higher located leaf area:
Ih = light intensity at height h, IS = light intensity above the forest,
Lh = total leaf area index from the top of forest to height h K = light extinction coefficient.
• Biomass losses are estimated in relation to tree biomass Kira, 1978; Yoda, 1983. Losses are
composed of renewal of roots, above-ground litter fall, and respiration of woody tree organs and leaves.
• The increments calculated for the representative trees change the size of the trees of a given
collective and determine the transitions of trees from lower to higher layers. •
Thus, size and stem number are recalculated for each species group in any of the height layers and patches. In simulation, this recalculation is performed at monthly time steps.
c. Competition
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