Forest Site Quality Evaluation in The United States

This chapter discusses several methods for estimating forest site quality together with the history, present status, and future goals in forest site investigation in the United States. In 1923 a committee of the Society of American Foresters recognized that volume production was the ultimate measure of site quality and recommended construction of yield tables for well-stocked natural forest stands. Site index based on height growth is now the most widely accepted method for estimating site quality in the United States. There are several methods for estimating site quality. Direct estimation of site index is based on height and age measurements from free-growing, uninjured, dominant, or dominant and codominant trees. These measurements are used with a family of height-age (site index) curves to estimate total height of trees at a specified index age. Indirect estimation of site index includes mensurational methods, plant indicators, physiographic site classification, synecological coordinates, soil-site evaluation, and soil surveys. Mensurational methods have been proposed for uneven-aged stands and for stands that lack trees suitable for directly estimating site index using conventional methods. The height growth of free-growing dominant and codominant trees is an indicator of site quality and thus can be considered as an integrator of the forest environmental features important for tree growth.