<P> The mean annual increment (MAI) or mean annual growth refers to the average growth per year a tree or stand of trees has exhibited / experienced to a specified age . For example, a 20 - year - old tree that has a diameter at breast height (dbh) of 10.0 inches has an MAI of 0.5 inches / year . MAI is calculated as M A I = Y (t) / t (\ displaystyle MAI = Y (t) / t) where Y (t) = yield at time t . Because the typical growth patterns of most trees is sigmoidal, the MAI starts out small, increases to a maximum value as the tree matures, then declines slowly over the remainder of the tree's life . Throughout this, the MAI always remains positive . MAI differs from periodic annual increment (PAI) because the PAI is simply the growth for one specific year or any other specified length of time . </P> <P> The point where the MAI and PAI meet is typically referred to as the biological rotation age . This is the age at which the tree or stand would be harvested if the management objective is to maximize long - term yield . The proof of this definition is shown by differentiating MAI (t) with respect to t, and is shown by Husch, Miller, and Beers </P>

Difference between current annual increment and mean annual increment