SORTIE-ND
Software for spatially-explicit simulation of forest dynamics

# Density Self-Thinning Mortality

This behavior calculates the probability of mortality of an individual juvenile tree as a function of the density and mean diameter of the neighborhood trees. Only neighborhood seedlings and saplings are taken into account in this behavior.

Trees killed by this behavior will have a mortality reason code of "natural".

### Parameters for this behavior

Parameter nameDescription
Density Self-Thinning Asymptote (A)The asymptote of the density self-thinning function.
Density Self-Thinning Density Effect (S)The parameter controlling the density effect of the density self-thinning function.
Density Self-Thinning Diameter Effect (C)The parameter controlling the effect of neighbor mean diameter of the density self-thinning function.
Density Self-Thinning Minimum Density for Mortality (#/ha)The minimum density of neighbors, in stems/ha, for density self-thinning mortality. A tree with a lower density of neighbors than this value will not die.
Density Self-Thinning Neighborhood Radius, in mThe maximum radius, in m, within which to search for neighbors to calculate neighbor density for density self-thinning.

### How it works

The probability of mortality is calculated with a double Michaelis-Menton function:

where:

• Pm is the probability of mortality for an individual tree
• density is the density of neighboring seedlings and saplings, in stems/ha, within a radius defined in the Density Self-Thinning Neighborhood Radius, in m parameter
• diam m is the mean diameter of neighbors, measured 10 cm above root collar in cm
• A is the Density Self-Thinning Asymptote (A) parameter
• C is the Density Self-Thinning Diameter Effect (C) parameter
• S is the Density Self-Thinning Density Effect (S) parameter

If the value of density is less than the value in the Density Self-Thinning Minimum Density for Mortality (#/ha) parameter, the tree does not die.

### How to apply it

This behavior can be applied to seedlings and saplings of any species. It cannot be applied to adults. This behavior can only be applied with a one year timestep.