Which statement best describes the site index in forest assessment?

• A. A measure of soil quality
• B. A forecast of annual growth without height data
• C. A map of site productivity
• D. A measure of the potential growth of trees in a given area based on the height of the dominant trees at a specified age

Answer: (D)

Site index describes the potential growth of trees in a given area, based on the height of the dominant trees at a fixed reference age. For a particular species, foresters measure how tall the dominant trees are at that chosen age (for example, 50 years), then use species-specific curves to assign a site index. A higher site index means the site is more productive for that species, reflecting favorable conditions like soil, moisture, and climate that allow greater height by the reference age. This concept is distinct from soil quality alone, isn’t a stand-alone forecast of annual growth without height data, and while it can be used to map productivity, its core definition is the height-at-age measure of dominant trees used to indicate potential growth.