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
• Two types of growth competition are defected in the model: competition for light and
space. Shading of larger trees affects the carbon production of each tree and the regeneration see Sections 2.2.2 and 2.2.4.
• The fraction of a patch covered by tree crowns is used as crowding index CI, which is
calculated for every canopy layer: d
i
= diameter of the with tree in a canopy layer, AP =spatial size of a patch
CD= crown-diameter-ratio.
Rahmawaty : Technology Journal Report on Selection System-A Critique on Long term Impacts…, 2006
USU Repository © 2006
• The tree mortality increases if the crowding index is higher than one crowding situation.
d. Regeneration and mortality
• Besides individual growth, the processes of seedling establishment and tree mortality are
also constrained by the local competitive situation. Both are therefore modeled on the patch level. The establishment of seedlings requires suitable micro-climatic conditions at
the forest floor.
• In FORMIX3, light intensity at the forest floor is used to control seedling establishment.
• Unfavorable growing conditions are reflected in low increments and lead to increased
mortality rates. Additionally, the crowding of trees of similar size, i.e. of trees in one height layer, is assumed to cause an increased rate of mortality.
e. Growth of the forest
• Individual tree growth, regeneration and mortality are the driving processes for the
simulation of the forest growth in each patch. •
Total stand dynamic is synthesized from the development of the single patches by adding their interaction.
3.3. Parameterization
• The FORMIX3 model was parameterized for the Dipterocarp forest of Deramakot Forest
Reserve. •
Some parameters are identified on the basis of general Dipterocarp forest characteristics reported in the literature, others are derived from locally available data or where
specifically measured Tables 2 and 3, see appendix.
3.3.1. Tree geometry
• The fixed ratios of the tree geometry model stem biomass to the trees total above-ground
biomass and crown diameter to stem diameter as well as the size dependent form factor are drawn from different studies in Dipterocarp forest in Malaysia and Indonesia and
checked by additional data from Sabah or Deramakot.
• The leaf area index LAI of individual tree crowns is estimated from global stand LAI data
and the typical size distribution of trees The light absorption coefficient K characterizing light attenuation in the crown is assigned its typical value
• The parameters of the biomass balance are critical, here especially those of
photosynthetic production as they describe the plants response to its light microenvironment. Therefore, quantum efficiency M and light saturated specific production
PMAX as parameters of the light response curve were measured for the five functional groups
3.3.2. Biomass balance
• The biomass loss rate does not describe the response to the competition situation, but
only determines the overall level of productivity. •
The author therefore could use the available data covering the processes of wood respiration, root renewal, and litter fall in Dipterocarp forest to derive an estimation of the
biomass loss rate.
Rahmawaty : Technology Journal Report on Selection System-A Critique on Long term Impacts…, 2006
USU Repository © 2006
• Within reasonable limits this value is then calibrated by comparing the simulated total
above-ground biomass of climax-state with respective data for primary forest at Deramakot.
3.3.3. Regeneration and mortality
• Similar conditions are met concerning the species group specific parameters of the
regeneration processes. Knowing that pioneer seed germination requires a considerable irradiance or, respectively, the suitable micro-climatic conditions indicated by an increased
irradiance, the level actually needed is calibrated by comparing the abundance of pioneer trees in the simulated climax state with respective data for primary forest at Deramakot.
For non-pioneer species only a minimum light requirement is assumed.
• Some detailed data exist for single species concerning the actual or potential
establishment rates of seedlings under the required conditions. These data reveal the large and partly systematic natural fluctuations of recruitment and the uncertainty that
therefore is to be expected to accompany any field data. Here, the respective parameter values for the single species groups can only be estimated from available data and again
are calibrated using observed numbers of established seedlings in primary forest.
• For pioneers the author use the same relationship, but increase mortality rates by a factor
of 8 to reflect much shorter lifetime of 30-40 years for the typical pioneers at Deramakot compared with several hundred years for non-pioneer species.
• In case of crowding, fixed mortality rates of roughly four times the average value for
seedlings or larger trees respectively are applied. •
The probability of dying trees to tumble and damage a patch of forest is calibrated by adjusting the gap fraction of simulated stand area in climax state with typical data for
primary forest with few natural disturbances as that at Deramakot.
• The gap formation by a falling tree is parameterized in analogy to investigations into the
damages caused by tree harvesting.
3.4. Model validation
• The model in combination with the parameterization for Deramakot was extensively tested
by comparison with empirical data. •
Table 4 gives an overview of the tested variables. One part of these tests investigates the structure and the stability of primary forest. Further tests focus on the growth of the forest
trees. In one test forest succession was analyzed using field data from different disturbed forest stands.
Table 4. Overview on the validation experiments performed with FORMIX3a
Rahmawaty : Technology Journal Report on Selection System-A Critique on Long term Impacts…, 2006
USU Repository © 2006
3.5. Logging scenarios
