Software for spatially-explicit simulation of forest dynamics

Double resource relative growth

This behavior uses a double Michaelis-Menton function to calculate relative growth based on two resources: light and a second resource. The identity of the second resource is unimportant and could be anything, from exchangeable calcium levels to soil moisture.

Parameters for this behavior

Parameter nameDescription
Asymptotic Diameter Growth (A)Asymptote of the Michaelis-Menton growth function at high light - function term A below.
Slope of Growth Response (S)Slope of the Michaelis-Menton growth function at zero light - function term S below.
Double resource - Influence of Resource (C)The parameter governing the influence of the second resource on the double-resource Michaelis-Menton equation.

How it works

Relative growth is calculated with the equation:


  • Y is the amount of annual relative growth
  • A is the Asymptotic Diameter Growth (A) parameter
  • S is the Slope of Growth Response (S) parameter
  • C is the Double resource - Influence of Resource (C) parameter, in units appropriate to the value of R
  • R is the amount of the second resource, in units appropriate to the value of C
  • GLI is the global light index, calculated by a light behavior

Growth is compounded over multiple timesteps with the equation:

G = ((Y + 1)T - 1) * diam


  • G is the amount of diameter growth for the timestep, in cm
  • diam is the diameter of the tree in cm (at 10 cm height if seedling or sapling, or DBH if adult)
  • T is the number of years per timestep

Note that setting the C parameter in the equation above to 0 eliminates the second resource and makes this equivalent to the "Non-limited relative growth" behavior.

The amount of the second resource is captured in a grid object called Resource. Currently it is up to you to enter a map of the values for this resource grid; for instructions on how to do this, see the Grid Setup Window topic. This behavior does not in any way alter the values in this grid.

How to apply it

This behavior can be applied to seedlings, saplings, and adults of any species. Any tree species/type combination to which it is applied must also have a light behavior applied. You must also enter a map of second resource values into the Resource grid. You can use either the diam with auto height or diam only version.