Light behaviors

Light is the key resource for trees in the SORTIE model. Consequently, great care is taken in SORTIE to calculate the amount of light that each tree gets - in fact, these calculations take up more processing time than any other during model runs.

There are two basic light index types used by SORTIE to describe the amount of light a tree receives. The first is the Global Light Index, or GLI. GLI is the percentage of full sun received at a point. The second index is the Sail Light index, which is the proportion of shade seen at a point, from none to total. (The name Sail Light comes from the fact that the shape of shading neighbor tree crowns is approximated by a 2D rectangle, like a sail).

How light calculations work

Behavior	Description
Average Light behavior	Averages GLI values to produce a set of values with a coarser spatial resolution.
Basal Area Light behavior	Calculates light levels as a function of the basal area of trees in a neighborhood.
Beer's law light filter behavior	Simulates a filter that reduces light according to Beer's Law.
Constant GLI behavior	Assigns a constant GLI value to all trees to which it is assigned.
Gap Light behavior	Shortcuts the light calculation process by considering GLI to be binary: either full light or no light.
GLI light behavior	Calculates a Global Light Index (GLI) value for each individual.
GLI Map Creator behavior	Calculates a GLI value for each cell in a grid to create a light map.
GLI Points File Creator behavior	Calculates GLI values for individual points in the plot.
Quadrat-based GLI light behavior	Calculates GLI for grid cells and assigns trees the GLI of their cell.
Sail light behavior	Calculates a Sail Light index value for each individual.
Storm Light behavior	Calculates light levels as a function of number of trees damaged in storms.