|GUIDELINES for||. . .|
|Developing Stand Density Management Regimes|
The trade-off between stand volume and piece size achieved through espacement, pre-commercial thinning and commercial thinning should be evaluated using stand and stock tables. However, in the interest of brevity, volume per hectare and average diameter (all trees and prime trees) will be used in the following example.
The simulated data in Figure 11a show that natural regeneration densities above about 1500 trees/ha cause only small changes in stand volume per hectare and average diameter at rotation age. Lower stocking regimes result in progressively larger trade-offs as establishment density declines below this threshold. That is, less volume is produced, but it is concentrated on fewer, larger trees. The volume-diameter threshold varies with species, regeneration method (natural regeneration or plantation), utilization standards, as well as other biological and ecological factors. Other information (e.g., economic analysis) is needed to determine the optimum regeneration density.
Figure 11. a) Harvest yield is much more sensitive to changes in regeneration density between 300 and 1500 sph than at higher densities. b) The trade-off between the mean diameter of all trees and stand volume occurs before crown closure. c) Prime tree average DBH is less sensitive to regeneration density than is stand average DBH.
The increase in average diameter resulting from wide inter-tree spacing occurs prior to stand crown closure [Figure 11b] with little or no increase thereafter attributable to establishment density. Since Figure 11 illustrates a stand espacement example, there is no artificial increase in diameter (i.e., chainsaw effect) immediately after treatment. The behaviour of prime trees in Figure 11c is similar, but much less dramatic.
Rotation ages in Figure 11a conform with the culmination of MAI. This ensures maximum sustained volume production. Planners may also use other criteria to determine the age of the final harvest. The attainment of a particular average diameter is a good example. However, they must be aware that technical rotations decrease the long-term stand volume production except in rare cases where the selected rotation age coincides with the culmination of MAI. At the forest level, planners have to consider trade-offs in terms of volume, diameter, rotation length and other relevant variables.
Copyright 1999 Province of British Columbia