SORTIE-NDSoftware for spatially-explicit simulation of forest dynamics
Competition mortality is a growth-based mortality behavior. It uses the results of the NCI growth behavior.
Trees killed by this behavior will have a mortality reason code of "natural".
Parameters for this behavior
How it works
NCI growth in SORTIE is calculated in the following way:
Max Growth is the maximum diameter growth the tree can attain, in cm/yr, entered in the NCI Maximum Potential Growth, cm/yr parameter. Size Effect, Shading Effect, Crowding Effect, and Damage Effect are all factors which act to reduce the maximum growth rate and will vary depending on the conditions a tree is in. Each of these effects is a value between 0 and 1.
In the Competition mortality behavior, the following measure is used as predictor variable for probability of mortality:
The relative increment is the ratio between the growth for an individual tree and the maximum growth possible for that tree. The Growth is the tree's growth for the previous timestep. PG is calculated as follows:
where Max Growth is the NCI growth parameter NCI Maximum Potential Growth, cm/yr, and SE is the Size Effect. Size Effect is calculated as follows:
Once the relative increment for an individual tree has been calculated, the probability of mortality for that individual is calculated in the following way:
All trees with a relative increment greater than or equal to max will live.
How to apply it
This behavior can be applied to saplings and adults of any species. It cannot be applied to seedlings. Any tree species/type combination to which it is applied must also have NCI growth. This behavior can only be applied with a one year timestep.