Simple and reliable models of density decrease with dominant height growth for even-aged natural stands and plantations

Abstract

Regular mortality (or self-thinning) is an integral part of woody plant dynamics, and the mortality model is one of the most important transition functions within dynamic growth models. The main objectives of the present study were to derive one-step stand-level mortality models for estimating the reduction in stand density with stand dominant height growth and to examine the applicability of the models in predicting regular mortality trends in even-aged natural stands and plantations. Four model formulations based on graphical examination of the main trends in the data and on defined desired properties of the selected mathematical functions were proposed and tested in algebraic difference equation form with two datasets from pine plantations and two datasets from natural broadleaved even-aged stands. The mortality patterns of three of the datasets were characterized by reverse sigmoid curves, while the forth dataset exhibited a reverse J-shaped trajectory. The models analyzed adequately represented the density decrease trends of the data through sets of polymorphic curves with multiple asymptotes. The dominant height-dependent mortality equations provide a simple and reliable approach to modeling the regular density decrease trends and can be considered for incorporation as a submodel within the framework of a dynamic Stand Density Management Diagram.