Age-class structure of forests
The age structure of a forest is the area of the forest consisting mainly of trees of the same age (i.e., by age class) or by proportions of trees in different age classes.
The age-class division used is dependent on the ages of trees of different species. For forest accounting purposes, it is useful to have the age-structure expressed in terms of timber volumes. This may be derived by combining values for the number of trees with data on the average volume of timber for a tree of a given age and species. Since the volume of a mature tree is much larger than for a young tree, the distribution of timber volume may be very different from the distribution of number of trees.
OECD. 2005. Glossary of Statistical Terms. Available here. [Accessed November 2013]