A Simulation of Equilibrium Diameter Distributions of Sugar Maple (Acer saccharum)

Abstract

Several different types of diameter distributions have previously been proposed as characteristic of forest stands in demographic equilibrium, but the ubiquitous character of natural disturbances makes it unlikely that the form of equilibrium distributions can be determined by field studies. In this study, existing diameter distributions of old growth, uneven-aged stands of sugar maple were projected forward in time using a model based on size-specific growth and mortality functions. Although the initial diameter distributions show deviations from a smooth, steeply descending curve, these deviations do not persist under simulated equilibrium conditions of constant sapling recruitment and no exogenous disturbance. Plots of these equilibrium curves on semilogarithmic and double logarithmic scales indicate that they deviate markedly from both the negative exponential and negative power functions, and most closely resemble rotated sigmoid curves. Major deviations from descending monotonic curves may be interpreted as evidence of past non-equilibrium conditions, but a straight-line diameter distribution on semilogarithmic or log-log scales should not be used as a standard for inferring the occurrence of past disturbance in this forest type.