• 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.
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• 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
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