This behavior uses the effects of neighbor competitiveness to influence growth rates for juvenile trees ("NCI" stands for neighborhood competition index). A tree's maximum potential growth rate is reduced due to competitiveness and other possible factors. This is very similar to NCI growth, but adapted for juveniles.
Parameter name | Description |
---|---|
Juvenile NCI Alpha | NCI function exponent. |
Juvenile NCI Beta | NCI function exponent. |
Juvenile NCI Crowding Effect Slope (C) | The slope of the curve for the crowding effect equation. |
Juvenile NCI Crowding Effect Steepness (D) | The steepness of the curve for the crowding effect equation. |
Juvenile NCI Diam10 Divisor (q) | The value by which neighbor d10s are divided when calculating NCI. This can be used to make units adjustments. |
Juvenile NCI - Include Snags in NCI Calculations | Whether or not to include snags when finding competitive neighbors for NCI. |
Species i Juvenile NCI Lambda Neighbors | The competitive effect of neighbors of species i on the target tree species's growth, between 0 and 1. |
Juvenile NCI Maximum Crowding Distance, in meters | The maximum distance, in m, at which a neighboring tree has competitive effects on a target tree. |
Juvenile NCI Maximum Potential Growth, cm/yr | Maximum potential diameter growth for a tree, in cm/yr. |
Juvenile NCI Minimum Neighbor Diam10, in cm | The minimum d10 for trees of that species to compete as neighbors. Used for all species, not just those using NCI growth. |
Juvenile NCI Size Effect "a" | Size effect power function scaling factor "a" parameter. |
Juvenile NCI Size Effect "b" | Size effect exponent "b" parameter. |
For a tree, the amount of diameter growth per year is calculated as:
Max Growth is the maximum diameter growth the tree can attain, in cm/yr, entered in the Juvenile NCI Maximum Potential Growth, cm/yr parameter. Size Effect and Crowding Effect are 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:
Crowding Effect is calculated as:
where:
The NCI value sums up the competitive effect of all neighbors with a d10 at least that of the Juvenile NCI Minimum Neighbor Diam10, in cm parameter, out to a maximum distance set in the Juvenile NCI Maximum Crowding Distance, in meters parameter. The competitiveness of a neighbor increases with the neighbor's size and decreases with distance. The neighbor's species also matters; the effect depends on the relationship between the target species and the neighbor species.
Unlike NCI growth, this competitiveness index uses d10 instead of DBH; so seedlings can compete. For adults, the d10 is calculated from DBH using the DBH - diameter at 10 cm relationship. You set whether or not snags compete in the Juvenile NCI - Include Snags in NCI Calculations parameter.
NCI is calculated as:
where:
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 d10 for one year. For each year, any portion of the growth equation with d10 as a term is recalculated with the previous year's updated d10 value. (NCI values are constant throughout this loop - for neighbors, only the d10 at the start of the timestep is used.) The final total growth amount is added to the tree's d10.
This behavior can be applied to seedlings and saplings of any species. You can use either the diam with auto height or diam only version.