Variable-density thinning in uneven-aged forest management - A case for Norway spruce in Finland

Abstract

Almost all commercial forests of Finland are simultaneously used for timber production, outdoor recreation and biodiversity maintenance. For the past 60 years, the official line of silviculture has been even-aged management. However, uneven-aged management and other forms of continuous cover forestry are gradually gaining popularity and also official acceptance. This study analyzed variable density thinning (VDT) in the context of uneven-aged management of Norway spruce (Picea abies L.Karsten) stands. The aim was to find economically profitable management systems, which would result in forests that are good for recreation and biodiversity maintenance. The stand compartment was divided into cutting segments and only one segment was harvested at a time. When economic profitability was maximized as the sole management objective, 15-year cutting cycle with uniform thinning (UT) was the optimal management system. All trees larger than 19 cm in diameter at breast height (all saw log-sized trees) were removed in the cutting. When a continuous presence of large trees was required, VDT was clearly more profitable than UT. In VDT, all large trees were removed from the thinned places but there were large trees in the segments that will be cut in the next logging operation. The optimal cutting cycle (interval between successive cuttings in the same place) of VDT was 20-30 years when large trees were required in the post-cutting forest. Several combinations of the length of cutting cycle and number of cutting segments were nearly equally profitable. Profitable options were, for instance, to divide the stand into four cutting segments each cut at 20-year interval or three segments each cut at 30-year interval. © Institute of Chartered Foresters, 2011. All rights reserved.