Gesetzmäßigkeit zwischen bestandesdichte und zuwachs. Lösungsansatz am beispiel von reinbeständen aus fichte (Picea abies [L.] karst.) und buche (Fagus sylvatica L.)

The relationship between stand density and growth is analysed empirically (Fig. 1-3) and modeled mathematically on the basis of long-term thinning experiments for Norway spruce and European beech. The revealed relationship between stand density and periodical volume growth follows a unimodal curve in principle, but depending on, i. a. observed range of density, ontogenetic stage, and site quality of the stand, we perceive only a particular (increasing or culminating) portion of the curve [Equations (4, 5)]. In juvenile phase a halving of stand density may raise current growth of spruce and beech by 9% and 23%, resp. Whereas spruce's growth reacts most positively on thinning under poor site conditions and with increment reduction on favourable sites, beech behaves in opposite. During ontogenesis the culmination point of both species' unimodal relation moves towards maximum density (Fig. 4). By integrating this density-growth-model in an algorithm for whole stand development (cf. Appendix) dependency of cumulative stand growth on different stand density scenarios can be elucidated. Cumulative volume growth achieved by maximum, optimal and long-term stationary density differs considerably, and how the different treatment variants come out depends on the respective time scale (Fig. 5). In juvenile stage cumulative volume growth can be raised to 130%, at age 120 just to 105% of the A-Grade. Optimal density assures maximum current growth period by period, but not necessarily the maximum cumulative volume growth. The reason for that paradox being, that treatment in early stage and reagibility in higher age form a nexus: Reduction of density enhance the growth and transport a stand earlier in an advanced allometric stage, so that its potential to react on thinning with transgressive growth subsides prematurely. Causes and practical consequences of the individual species relationship between stand density and volume production are discussed.