Why Quadratic Mean Diameter

Quadratic mean diameter is the measure of average tree diameter conventionally used in forestry, rather than arithmetic mean diameter. The historical and practical reasons for this convention are reviewed. West. J. Appl. For. 15(3):137-139. Average diameter is a widely used stand statistic that appears in virtually all yield tables, simulator outputs, stand summaries, and much inventory data. To most people, aver- age is synonymous with the arithmetic mean, defined as arithmetic mean = Z = (E x i) / n where thexi are the individual measurements and n is the total number of measurements. But there are in fact some half dozen different kinds of averages (= means = measures of central tendency), each appropriate to specific uses. One of these is the quadratic mean (Kendall and Buckland 1967, Iles and Wilson 1977), defined as