Stand density and growth of Norway spruce (Picea abies (L.) Karst.) and European beech (Fagus sylvatica L.): evidence from long-term experimental plots

Berlin

2005

S. 193-205

9 Abb., 5 Tab., 50 Lit. Ang.

Artikel aus einer ZeitschriftUnselbständiges Werk

200136714

On the basis of nine Norway spruce (Picea abies (L.) Karst.) and ten European beech (Fagus sylvatica L.) thinning experiments in Germany, for which both residual and removed stock had been registered first during 1870, I scrutinize how moderate and heavy thinning from below (B-, C-grade) affects the production of merchantable volume compared with light thinning (A-grade). In relation to A-grade, cumulative merchantable volume (CV) of B- and C-grade amounts in average to 103-107 percent in juvenile and to 97-102 percent in mature Norway spruce stands. The corresponding findings for European beech are 101-106 percent and 94-102 percent. CV of individual stands varies between 89 percent and 130 percent for Norway spruce and 73 percent and 155 percent for European beech (CV of A-grade = 100 percent). These findings are substantiated by the relation between stand density (SDI) and periodic annual increment (PAI). On the B- and C-grade plots of spruce and beech, respectively, SDI was reduced down to 41-91 percent and 31-83 percent of the A-grade. When SDI is reduced in young stands, PAI follows a unimodal curve. Norway spruce's PAI culminates in 109 percent if SDI is reduced to 59 percent; European beech's PAI culminates in 123 percent when density is reduced to 50 percent. Whereas Norway spruce's growth reacts most positively on thinning under poor site conditions and with increment reduction on favourable sites, European beech behaves oppositely. With stand development the culmination point of the unimodal relation moves towards maximum density, so that in older stands PAI follows the increasing pattern, which is the left portion of a unimodal curve. A model is presented which apparently unifies contradictory patterns of stand density-growth reactions by integrating relative stand density, average tree size and site fertility effects, and makes the findings operable for forest management.