Predicting Regeneration Quality

Quality of reproduction is commonly defined in terms of the acceptability of growing stock. Before adequacy of regeneration potential can be assessed, it is necessary to define acceptable growing stock, which requires a consideration of species and tree characteristics. Commonly used tree characteristics are height, diameter, and crown class. Although a qualitative characteristic, crown class is a concept with which most foresters are familiar. It is a widely used descriptor of trees because it facilitates visualization of a tree's social status more easily than diameter or height measurements, per se. For example, the definition of acceptable growing stock may be limited to certain species and trees that occupy only codominant and dominant crown classes. ACORn solves that problem by projecting future diameter and survival of individual trees by diameter and crown classes to stand age 21.

Some foresters may consider only codominant and dominant trees as acceptable growing stock. Others may consider trees that are intermediate or larger as acceptable. To integrate this decision into the regeneration model, a threshold tree diameter is defined that classifies trees into one of the two user-defined crown class categories: acceptable or unacceptable. When acceptable growing stock includes only codominant and dominant trees, tree diameters equal to or greater than 3.8 in. are classified as codominant or dominant at stand age 21. When acceptable growing stock is defined as trees that are intermediate or larger, trees with diameters less than 2.6 in. are classified as suppressed, and those with larger diameters are classed as acceptable growing stock. In this way, ACORn incorporates crown class to project twenty-first-year diameter distributions.