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).
| 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. |