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

# Browsed relative growth behavior

This behavior simulates herbivory by allowing trees to grow at different rates when browsed versus unbrowsed.

### 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.
Relative Michaelis-Menton Growth - Diameter ExponentThe exponent to be used with diameter when calculating relative growth.
Browsed Asymptotic Diameter Growth (A)Asymptote of the Michaelis-Menton growth function at high light when a plant has been browsed.
Browsed Slope of Growth Response (S)Slope of the Michaelis-Menton growth function at zero light when a plant has been browsed.
Browsed Diameter ExponentThe diameter exponent for growth when a plant has been browsed.

### How it works

Trees grow according to the relative growth version of the Michaelis-Menton function. The same function is used for both browsed and unbrowsed trees, but the parameters are different. The function is:

where:

• Y is the amount of annual relative growth
• A is the Asymptotic Diameter Growth (A) or Browsed Asymptotic Diameter Growth (A) parameter
• S is the Slope of Growth Response (S) or Browsed Slope of Growth Response (S) parameter
• 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 X

where:

• 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
• X is the Relative Michaelis-Menton Growth - Diameter Exponent or Browsed Diameter Exponent parameter

Whether or not a tree is browsed is determined by the Random browse behavior.

### 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 and the Random browse behavior applied. You can use either the diam with auto height or diam only version.