In forestry, the relationship between the age of a stand of trees and the yield (timber volume) in that stand are described with the following "yield equation":

where

· y = k e (y = yield, e is the base of natural logarithms),
· A = stand age, and
· k and b are constants that depend on the type of stand (species, geography, etc.).

The following graph shows a typical yield curve.

The forester must determine the age at which trees ought to be harvested to sustain the forest and maximize the profitability of land. This optimal age is known as the Mean Annual Increment (MAI).

The forester must graph the MAI and show that the curve does have a maximum at this point.