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

Puerto Rico storm bi-level growth - diam with auto height

Puerto Rico storm bi-level growth - diam with auto height

This behavior increments growth according to two possible growth equations, one to be used in low-light conditions and the other to be used in high-light conditions. This behavior was originally created for the Puerto Rico model.

Parameters for this behavior

Parameter nameDescription
PR Storm Bi-Level - Threshold for High-Light Growth (0 - 100)The threshold between low-light and high-light equations, as a value between 0 and 100.
PR Storm Bi-Level - High-Light "a"The "a" value in the high-light growth function.
PR Storm Bi-Level - High-Light "b"The "b" value in the high-light growth function.
PR Storm Bi-Level - Intercept for Low-Light Growth (a)The intercept of the linear growth function used in low-light conditions.
PR Storm Bi-Level - Slope for Low-Light Growth (b)The slope of the linear growth function used in high-light conditions.

How it works

Light levels come from the Storm Light grid produced by the Storm Light behavior. The threshold between the use of the high-light and low-light functions is set in the PR Storm Bi-Level - Threshold for High-Light Growth (0 - 100) parameter.

The function used in low-light conditions is:

Y = (a + b * diam) * T

where

• Y = amount of diameter growth in cm
• a = PR Storm Bi-Level - Intercept for Low-Light Growth (a) parameter
• b = PR Storm Bi-Level - Slope for Low-Light Growth (b) parameter
• diam = diameter (diameter at 10 cm for seedlings and saplings, DBH for adults)
• T = number of years per timestep

The function used in high-light conditions is:

H = T * a * diam * e(-b * N)

where

• H = amount of height growth, in cm
• a = PR Storm Bi-Level - High-Light "a" parameter
• b = PR Storm Bi-Level - High-Light "b" parameter
• diam = diameter (diameter at 10 cm for seedlings and saplings, DBH for adults)
• N = number of years since the last storm, from the Storm Damage grid produced by the Storm disturbance behavior
• T = number of years per timestep

H is expressed in centimeters of height growth. This is transformed into a number of cm of diameter growth, which is what this behavior passes along. This means that during tree life history stage transitions, the height the tree ends up with is not guaranteed to match the height calculated by the high-light growth function.

How to apply it

This behavior can be applied to seedlings, saplings, and adults of any species. You must also use the Storm disturbance and Storm Light behaviors.