Finnish Forest Research Institute  Metla

Press release 30.03.2006

Heterogeneous stands should be thinned sooner than homogenous ones

Forest management instructions designed for homogeneous stands are not directly applicable to heterogeneous stands. For example, first thinnings should be carried out in heterogeneous pine stands sooner than current recommendations dictate, but later than recommended in exceptionally homogeneous stands. The findings are a result of a joint study by the University of Joensuu and the Finnish Forest Research Institute.

Thinning schedules based on predominant height of the stand stock and the basal area should be different for homogeneous and heterogeneous stands. A heterogeneous stand may contain groups of trees that should be thinned, even though the basal area of the whole stand may still be below the thinning threshold. This means that heterogeneous stands should be thinned at a lower basal area than homogeneous stands. If a heterogeneous stand contains very sparse areas, the remaining basal area of the stand will also be lower than in homogeneous stands.

The study outlines a method allowing taking into account the heterogeneity of a stand in a forest configuration, i.e. stand density and other within-stand variation, in optimising the cutting schedule. The method was applied to examine how an optimal management schedule of a stand is determined by within-stand variations in spruce and pine stands.

Optimal solutions of heterogeneous stands clearly diverged from results obtained for homogeneous stands. Heterogeneity of the stand brought forward the first thinning and reduced optimal density of the remaining stand, particularly in spruce stands. With spruce, heterogeneity of the original stand also clearly brought forward the second thinning, even though the first thinning considerably reduces the stand heterogeneity. Heterogeneity of the original stand reduced logging revenues and cutting yield of the stand, regardless of efforts to even out within-stand variation at first thinning. The results showed that management schedules drawn up for homogeneous stands are not as such applicable to heterogeneous stands. The results may be used in support of updating current forest management recommendations.

Publication: Pukkala, T. & Miina, J. 2005. Optimising the management of a heterogeneous stand. Silva Fennica 39(4): 525-538.

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