A stand density management diagram is a simple biological model relating forest yield to forest density at any stage of a particular forest stand's development. Stand density management diagrams are used in forest management and designed to use a current stand's density to project its future yield. One major reason for the effectiveness of density management diagrams is the relatively low effect of site variance on the diagram’s shape. Density management diagrams have transformed ideas long held in traditional stocking diagrams. In 1967, Samuel F. Gingrich published his idea of comparing basal area per acre, trees per acre, and quadratic mean diameter in one graph. He called this the stocking diagram. These same principles are used to make the stand density management diagram work. Basal a