Soils vary greatly in their ability to produce merchantable volumes of pulpwood, sawtimber, veneer, poles, piling or other wood products in a reasonable period of time. In fact, as with any other crop, the better the land, the more productive the forest. Landowners must be aware of soil factors that affect forest production before investing in forest regeneration or management. The collective influence of soil factors will determine the site index for a particular tree species on a given soil area. Site index is the total height to which dominant trees of a given species will grow on a given site at some index age, usually 50 or 25 years in the Southeast.
Dominant trees are the tallest trees in the stand.
If it is stated that an area has a site index for loblolly pine of 70 feet at 50 years, then we expect loblolly seedlings planted on that area today to be 70 feet tall in 50 years. Index age and tree species must be stated when referring to site index because the site index of one species will be different from the site index of another species growing on the same area. There is a close relationship between site index and timber yield. The depth of the uppermost soil layer is a critical factor affecting tree growth. Topsoil is highest in organic matter and nutrients, is usually well aerated and drained, and allows maximum root growth and root penetration.