The Trinity of Norms.

The “Normal Forest” is a theoretical condition where the growing stock of trees has a more or less even series of age classes, with an even spread of tree sizes, with full stocking on each site growing with normal increments (AKA –  The Trinity of Norms).

The idea of the normal forest emerged in the 1800s in Germany as a simplified mathematical framework for forest management, particularly to produce timber.  It works best for single aged stands rather than complex multiple aged forests.

For example, in a hypothetical 100-ha forest, where each age class is equally represented in 1ha plots from 0-100 years, and each hectare is fully stocked and grows normally at 1 m3/ha/year, then each plot will carry 100 m3 of timber at age 100. Then if the harvesting rotation is 100 years, a mature 1 ha plot can be cut each year and then replanted, which will yield 100 m3 per year in perpetuity.

A normal forest serves as a doctrine of faith that allows for a balance of growth that matches the area harvested and creates an even and sustained yield of timber. It also serves as a standard to which actual forests can be compared.

The normal forest is possible in managed short-rotation softwood plantations but is not found in Australian native forests, particularly when they have either been heavily harvested in the past, like the Wombat State Forest during the gold rush, or burned by extensive bushfires, such as the ash forests in the Central Highlands which have large stands of uniform, single-aged, 1939 and 1983 regrowth.