Potential relative increment (PRI): a new method to empirically derive optimal tree diameter growth

Potential relative increment (PRI) is a new method to derive optimal diameter growth equations using inventory information from a large public database. Optimal growth equations for 24 species were developed using plot and tree records from several states (Michigan, Minnesota, and Wisconsin) of the north central US. Most species were represented by thousands of individuals measured across an extensive geographic region that presumably covered a large range of possible environmental conditions. Thus, it was assumed that the individuals growing at the highest rate for each diameter class represented a reasonable estimate of size-specific optimal growth. Comparison of PRI equations among several hardwood and conifer species of differing shade tolerance indicated that unique patterns of optimal diameter growth result. The PRI methodology is similar to other optimal growth models in both shape and trends of predicted growth, but is easier to calculate and offers more flexibility than many other designs.