EFISCEN is an area-based matrix model. For each forest type that is distinguished in the input data (which might be according to species, region, site class and owner), a separate matrix is set up. One matrix consists of 60 age classes of 5 year width and 10 volume classes with widths that vary depending on the forest under study.
Aging of the forest is simulated by moving area to a higher age class, while growth is simulated by moving the area to a higher volume class. Transition chances are derived from increment figures from the input data, or from growth and yield tables. These transitions can be changed over time to simulate changes in growing conditions, like climate change.
Thinning in the model is simulated by moving area one volume class down. Only area that was moving to a higher volume class (increment) can be subjected to thinning. The user can specify an age range where thinnings can be carried out. If a thinning will be carried out or not depends on the actual demand for thinnings. A user-defined fraction of the area that has been subjected to a thinning will be moved up one volume class extra to simulate the growth response after a thinning.
Final fellings are simulated by taking the area out of a certain cell. Final felling chances can be set by the user as a function of age and volume class. The fraction that is actually harvested depends on the actual demand for wood from final fellings.
Area that is taken out of the matrix is put in a separate class, the non-stocked area. Regeneration is simulated as the movement from the non-stocked area into the lowest age and volume class of the matrix.
Natural mortality is simulated by moving a fraction of the area in a certain cell one volume class down. This fraction can be set by the user as a percentage of the growing stock, varying by age class. The actual fraction of the area that is moved down will then depend on the average volume before, and the difference between the volume classes. Only area that has not recently been thinned can be subjected to natural mortality.
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