Growth of Oaks in Southeastern Iowa in Relation to Stand Density and Grazing

High yields of wood depend upon maintaining forest stands of optimum density and providing levels of water, nutrients, light and heat sufficient for the full development of different species as determined by their genetic potentials. European studies of growth in relation to stand density have yielded somewhat contradictory results. Møller (1954) indicates that growth increases with increasing stand density up to about 50 or 60 percent of the maximum attainable density; beyond this there is either no change or a slight decrease in growth depending upon the criterion for growth used. Assmann (1955) and Mitscherlich (1954) have found maximum growth at 80 to 95 percent of maximum stand density with growth decreases at higher and lower densities. Most authors agree, however, that there is at least a narrow range of stand densities over which the differences in growth are small. Heavy grazing in hardwoods often lowers the density of stands and changes the soil, climatic and biotic environment of the trees. The soil is compacted with simultaneous changes in pore-space relationships. Infiltration of water is reduced and aeration affected. Some root injury generally occurs. The original understory vegetation is destroyed and a gradual reduction in the density of the main stand may occur, the results of which are increasing solar radiation within the stand, increasing temperatures and wind movement, higher vapor pressure deficits at the ground line and the transpiring surfaces of leaves, and increasing dryness. The purpose of the present study was to determine the effects of continued heavy grazing and reduction in stand density on the height, diameter and volume growth of trees in the oak-hickory forests of southeastern Iowa