Over the years, forestry sciences have developed a classification system for quickly summarizing the tree growing potential of a site. Sites may differ significantly in soil quality, nutrients, water availability, and environmental conditions, enabling the same seed to grow far stronger and larger in one location than another.
A Forest Site Index summarizes this concept. The National Resource Conservation Service (NRCS) provides generalized site index information as part of its web survey application (websoilsurvey.nrcs.usda.gov/app). In our area, the most frequently used Site Index represents the anticipated height (in feet) of a Douglas fir tree after 50 years of steady growth from a seedling on the site.
For our property, the Site Index is around 92. This is about an average Site Index number, which is somewhat surprising given the size and health of the trees there. However, a past owner’s proactive thinning has certainly aided the forest, and also the NRCS data is of course generalized at the macro level so there will still be site specific differences at the more micro property level.