Slide 12: Effect of trees on grass
In savannas, the presence of trees has a powerful suppressive effect on grass production, due to competition. This effect is almost always non-linear - the first increments of tree biomass have a greater suppressive effect than the last ones. The degree of curvature depends on site conditions. A form for this curve can be derived from first principles regarding the way trees and grass carve up the space in savannas. Here is a simplified solution for a particular set of assumptions regarding tree canopy radius and rooting radius. In this equation, P is the fraction of grass primary productivity in relation to P0, the productivity of an untreed area, and BA is the total basal area of trees in square metres per hectare.