|GUIDELINES for||. . .|
|Developing Stand Density Management Regimes|
A number of different types of planning tools are available to assess stand density management options. These decision support tools range from simple "look-up" tables to sophisticated computer simulation and optimization models. Most models require a starting point or "seed" to define the initial conditions or state of the activities being modelled. In addition to a starting point, they may require an "end" point, or final condition that must be achieved at the end of the planning period.
The accuracy of all decision support tool predictions is determined largely by the quality of the information and data used in the analysis. Shortcomings are often caused by the limitations of each tool, lack of reliable information and inappropriate assumptions, and misuse or misunderstanding by the user. The following discussion describes the tools that are available, the type of analysis they perform, and the information each requires.
Growth and yield models provide stand age or height projections of stand growth parameters, such as height, average diameter, basal area, stocking density and timber volume. The most important model outputs, in terms of utility for stand density management decisions, are stand (tree size distribution) and stock (stand volume distribution) tables. These output tables are helpful for comparing the stand growth responses of several stand density treatment options.
Some of these models may allow the direct or indirect analysis of wildlife habitat as measured by environmental indicators.
Stocking guides represent the generalized output of more sophisticated and detailed growth and yield models. They display information in the form of look-up tables, that allow the user to anticipate the effects of different treatments on stand characteristics. They do not, however, allow the user to modify the background data or model assumptions, or perform sensitivity analysis.
Stand density management diagrams display, on a single graph, the relationships between stand density, top height, quadratic mean diameter and mean tree volume. The data used in their construction are based on average values usually produced by growth and yield models. Users must estimate the relationship between the graphed variables and time using site index curves. A more complete description of stand density management diagrams, and their uses and limitations are available in Farnden (1996).
Stand density management diagrams have the same limitations as the models or data they are based on: they depict only single-species, single layer, even-aged stands, and provide stand average values rather than stand and stock tables.
Copyright 1999 Province of British Columbia