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Timber Supply Modeling

The modeling component of FSSAM performs the actual growth and harvest simulation modeling for the management unit. This process first requires setting the harvest targets for each of the years for which the simulation is to be carried out. Then for each year, a three-stage cycle of operations is performed. In the first stage, the volumes and other attributes of the stands and other spatial units are updated. In the second, harvesting is performed: an initial pass is made through all the landscape units in the management unit; the results are examined, and, if the harvest targets are not met, additional harvesting passes are made through those landscape units with spare capacity, to try to reach the overall target. In the third stage, summary results for the time period are saved in preparation for reporting.

Some of the characteristics of this modeling system are as follows:

  • The targets for the individual landscape units are set from the overall target for the management unit, based on area or forest state parameters.
  • Growth of the individual stands is modeled based on volume tables.
  • Both biodiversity and generic age-area constraints can be applied (e.g., at most 15% of the area can be less than 20 years old). This allows the setup of old growth, visual quality, watershed, habitat and many other types of constraint. Utility functions can also be set up to apply to the constraints.
  • Green-up constraints can be made to apply, in which case cutting of a block adjacent to a recently harvested block must wait until sufficient time has passed for this block to green up.
  • Following cutting, the stands can be populated with species that are different from those in the original forest cover, and different growth rates for the regenerated stands can be specified.
  • Several harvest schemes are available, including those based on leading species, sawlog volumes, salvage priority and a general category priority. Some of these affect both the harvest queuing and the setting of the individual targets for the landscape units.
  • Patch metrics may be computed for the blocks.
  • The road network can be progressively built up during the simulation (i.e., not-yet-built segments can be built and added to the existing network), with construction during a time period limited by a road-building budget.
  • Detailed reporting may be performed, with various classes of reports being available.
  • The modeling may be done as a component of an optimization scheme, to maximize the overall volumes harvested subject to the constraints.
  • Options are provided to run the model on a single local host or in a distributed environment using an internal IDL-based sockets communication scheme. If the distributed option is chosen, the ability to perform automated load balancing of the landscape unit data is provided. Also, a Web server option (Java client interface) has been developed.
  • The model may be run using the IDL Development Environment or the (no-charge) IDL Virtual Machine
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