Ertragskundliche Aspekte und Strukturdynamik der Buchen-Lichtwuchsdurchforstung

Abstract

Effects of heavy selective thinnings in beech stands with regard to stand productivity and structural diversity Based on thinning trials in beech stands initiated in the early 1970s, the effects of selective thinnings in favour of 100 to 120 future crop trees were analysed with regard to volume productivity and the stands' structural diversity. The results show that these kinds of thinnings reduce volume productivity by approximately 6% compared to the maximum volume growth. The reduction in volume growth is mostly caused by the fact that the strongly released crop trees have reduced their height growth for the benefit of a lateral crown expansion, while basal area growth was not affected. Calculations indicate that silvicultural systems working with only 50 future crop trees per hectare may decrease the maximum volume production by about 12%. Furthermore, the results show that the intense crown releases caused by selection thinnings increase the horizontal and vertical diversity of beech stands, since the trees in the understorey profit from better light conditions. The indices calculated for diameter and height diversity of the selection thinning plots approach the values being typical for single tree selection forests (“Plenterwälder”). Already after three to four consecutive selection thinnings, the beech stands' diameter distributions displayed an exponentionally decreasing shape typical for single tree selection forests close to equilibrium. Growth simulations revealed that it might even be possible to directly transform beech stands by selection thinnings into single tree selection structures. However, presumably negative effects on timber quality to be expected under single tree selection structures should be considered as a critical aspect with regard to theoretically possible transformation.