This behavior uses the effects of neighbor competitiveness to influence growth rates ("NCI" stands for neighborhood competition index). A tree's maximum potential growth rate is reduced due to competitiveness and several other possible factors. You can use certain parameter values to turn these influences on and off to reflect the conditions appropriate for your run.
Parameter name | Description |
---|---|
NCI Alpha | NCI function exponent. |
NCI Beta | NCI function exponent. |
NCI Crowding Effect Slope (C) | The slope of the curve for the crowding effect equation. |
NCI Crowding Effect Steepness (D) | The steepness of the curve for the crowding effect equation. |
NCI Damage Effect - Complete Storm Damage (0-1) | The fraction by which a tree's growth rate is reduced when it has sustained complete storm damage. Set this to 1 if you are not including storms in your run. |
NCI Damage Effect - Medium Storm Damage (0-1) | The fraction by which a tree's growth rate is reduced when it has sustained medium storm damage. Set this to 1 if you are not including storms in your run. |
Species i NCI lambda neighbors | The competitive effect of neighbors of species i on the target tree species's growth, between 0 and 1. |
NCI Maximum Crowding Distance, in meters | The maximum distance, in m, at which a neighboring tree has competitive effects on a target tree. |
NCI Maximum Potential Growth, cm/yr | Maximum potential diameter growth for a tree, in cm/yr. |
NCI Minimum Neighbor DBH, in cm | The minimum DBH for trees of that species to compete as neighbors. Used for all species, not just those using NCI growth. |
NCI DBH Divisor (q) | The value by which neighbor DBHs are divided when calculating NCI. This can be used to make units adjustments. |
NCI Neighbor Storm Damage (eta) - Complete (0-1) | The fraction to which a neighbor's competitive effect is reduced when the neighbor has sustained complete storm damage. Set this to 1 if you are not including storms in your run. |
NCI Neighbor Storm Damage (eta) - Medium (0-1) | The fraction to which a neighbor's competitive effect is reduced when the neighbor has sustained medium storm damage. Set this to 1 if you are not including storms in your run. |
NCI Shading Effect Coefficient (m) | The coefficient in the shading effect equation. Set this value to 0 if you do not wish to use shading. |
NCI Shading Effect Exponent (n) | The exponent in the shading effect equation. If you set the NCI Shading Effect Coefficient (m) parameter to 0, this value is ignored. |
NCI Size Effect Mode, in cm (X0) | The mode of the size effect curve. |
NCI Size Effect Variance, in cm (Xb) | The variance of the size effect curve. |
NCI Size Sensitivity to NCI (gamma) | The sensitivity of a tree's growth rate to its DBH. Set this to 0 to remove the DBH term altogether. |
Include Snags in NCI Calculations | Whether or not to include snags when finding competitive neighbors for NCI. |
For a tree, the amount of growth per year is calculated as:
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 optional 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.
Size Effect is calculated as:
where:
Shading Effect is calculated as:
where:
This effect is not required. To omit the Shading Effect, set the NCI Shading Effect Coefficient (m) parameter to 0.
Crowding Effect is calculated as:
where:
The NCI value sums up the competitive effect of all neighbors with a DBH at least that of the NCI Minimum Neighbor DBH, in cm parameter, out to a maximum distance set in the NCI Max Radius of Crowding Neighbors, in m parameter. The competitiveness of a neighbor increases with the neighbor's size and decreases with distance and storm damage to the neighbor (optional). The neighbor's species also matters; the effect depends on the relationship between the target species and the neighbor species. Seedlings never compete. You set whether or not snags compete in the Include Snags in NCI Calculations parameter.
The crowding effect is optional. You can omit it by setting either the NCI Crowding Effect Slope (C) or NCI Max Radius of Crowding Neighbors, in m parameters to 0.
NCI is calculated as:
where:
The value of Damage Effect is optional. If you elect not to use storms in your run, set all values in the NCI Damage Effect - Medium Storm Damage (0-1) and NCI Damage Effect - Complete Storm Damage (0-1) parameters to 1. If you are using storms, then the value of Damage Effect depends on the tree's damage category. If the tree is undamaged, Damage Effect equals 1. If the tree has medium storm damage, the value is the NCI Damage Effect - Medium Storm Damage (0-1) parameter. If the tree has complete storm damage, the value is the NCI Damage Effect - Complete Storm Damage (0-1) parameter.
The amount of growth is in cm/year. For multi-year timesteps, the behavior will calculate total growth with a loop. Each loop iteration will increment DBH for one year. For each year, any portion of the growth equation with DBH as a term is recalculated with the previous year's updated DBH value. (NCI values are constant throughout this loop - for neighbors only the DBH at the start of the timestep is used.)
This behavior can be applied to saplings and adults of any species. It cannot be applied to seedlings. You can use either the diam with auto height or diam only version.
If the Shading Effect term is activated in the growth equation, then the trees to which this behavior is applied must also have a light behavior applied - the Sail light behavior is the one designed to work with the NCI behavior. The use of any other light behavior is at your own risk.
If any storm damage parameters are set to anything other than 1, it is recommended (but not required) that you have the Storm damage applier behavior applied.