This article evaluates and compares existing site index equations applicable to redwood and Douglas-fir in California’s north coast redwood forest. The authors find previous site index models for redwood to be biased, particularly in younger age classes. They therefore developed new polymorphic site index equations for this species, using both stem analysis and permanent plot data from Humboldt, Del Norte, and Mendocino counties. The new curves use a 50-year breast-height (4.5-foot) age as a base.

For Douglas-fir, tests showed King’s site index model for Douglas-fir in Washington and Oregon to be unbiased and adequate for Douglas-fir site index estimation in the north coast. Also, for cases in which appropriate site index trees are available for only one species, the authors give equations to predict redwood site index from Douglas-fir site index or to predict Douglas-fir site index from redwood site index.