|GUIDELINES for||. . .|
|Developing Stand Density Management Regimes|
Density management techniques such as espacement and thinning manipulate the growing space and resources available to each tree. These silviculture treatments control crown and root development, the size and quality of each tree and the productivity of the stand. The following discussion focuses on the concepts underlying espacement and thinning (pre-commercial and commercial).
Plantation espacement in BC since 1940 ranged from about 2 m (2500 trees/ha) to 4 m (625 trees/ha). Tree-to-tree spacing in natural stands covers a much wider range and is much less regular. Full site occupancy is achieved quickly if the establishment density is moderately high and the spatial distribution of trees is uniform. Uniformity increases in importance as establishment density decreases. Site occupation by tree crowns (Figure 4a) and merchantable volume (Figure 4b) decline in response to decreasing establishment density. Any clumping of the same number of stems will reduce the stand yield even further. Holes often reflect microsite limitations or brush competition.
Note that it is the unoccupied growing space or "holes" in the stand canopy that reduce timber yield-not the clumpiness itself. Low density stands produce less volume initially because there are too few trees to exploit the available growing space. The rate of stand growth improves after crown closure.
Theoretically, the growth rate of a low density stand could eventually surpass that of a dense stand, as predicted by yield projection models. This phenomenon, called cross-over, has not been observed in research plots in BC, which are still too young to confirm or reject the theory. Ministry data and models predict that cross-over is not likely to occur until well beyond rotation ages based on the culmination of MAI.
Figure 4. Espacement affects a) site utilization and b) volume production.
Copyright 1999 Province of British Columbia