Modelling the demographic sustainability of pure beech plenter forests in Eastern Germany

Abstract

The aim of this study is to scrutinise whether a dynamic equilibrium model based on sustainability of the demography is valid for pure beech plenter forests. Broad-leaved trees in general, and beech in particular react differently to individualisation and to shade than conifers, because of differences in space occupancy and their reaction to shade. Therefore application of the plenter system (or selection system) presents other constraints than for conifers forests. Sustainability must be assessed at stand level, because the plenter system functions without cover interruption and so needs continuous recruitment growing from the stand bottom up. The algorithm used for determination of demographic equilibrium depends on knowledge of the recruitment from below, stem migration over time (dependent on diameter increment), and removal for cultural and harvesting purposes and their dependency from stand density. Data used in this study comes from three permanent research plots in the pure beech plenter forests of Langula (Thuringia basin, Eastern Germany). The determination of the optimal stand density ensuring equilibrium uses an incremental growth model based on a basal area oriented density index (GCUM). It emphasises the phenomenon of growth extinction with increasing stand closure. Equilibrium is gained for a standing volume about 250 m3/ha and Basal area 22 m2/ha. This occurs at a much lower stand density than for classical coniferous plenter forests. The reasons for these differences and the silvicultural consequences are discussed. © INRA, EDP Sciences, 2006.