Size-class Structure of Old-growth Forests in Indiana

Stand attributes of 19 old-growth hardwood stands in the midwest are compared; bottomland stands range up to 199 sq ft and upland ones up to 152 sq ft in basal area per average acre. Number of stems per acre when plotted on semi-logarithmic paper according to size-class distribution gave no perfectly straight line, characteristic of a balanced distribution. Four patterns of configuration were recognized: (1) a nearly straight line indicative of relatively little stand disturbance, (2) a sharp break in the line indicative of severe disturbance at the particular size classes, (3) a curve characterized by a plateau indicative of significant recovery after disturbance, and (4) a line with a widely deviating negative slope indicative of a later stage in recovery. A straight line, fitted to the data by the least squares method, was interpreted to represent the overall present condition of the stand. Estimates of the undisturbed condition were made by comparing various portions of the line connecting the plotted points with the regression line. The coefficient of determination was taken as an index of the degree of disturbance in the stand. Comparison of the same stand before and after a 10-year interval supported conclusions derived from comparing different stands.