Diversität und produktivität von wäldern

This contribution focuses on the question how tree species richness is related to forest productivity. Based on long-term experimental plots the effects of the transition from mono-cultures to mixed stands are analysed. Important commercial tree species from temperate and boreal climate zones are considered. Depending on the type of mixture and site conditions the effects from species mixtures on productivity may vary considerably (Fig. 2). Combinations of early and late successional tree species, ontogenetically early and late culminating species, shade-intolerant and shade-tolerant species may raise the efficiency of resource utilisation by up to 30% compared with that in pure stands. By contrast, where ecological amplitudes and functional characteristics are similar, species will compete for the same resources in crown and root system. Antagonistic effects from species interaction and productivity reductions by up to 30% may ensue (Fig. 6). With the occurrence of risk the productivity relationships between pure and mixed stands, related to medium stand densities, may experience a shift in favour of mixed stands (Fig. 7 and 8). The reason being that the combination of several species is synonymous with risk distribution. As a rule, mixed stands are more flexible in the face of changes in site conditions and more resilient to natural disturbances or perturbations on account of silvicultural treatment (Fig. 9). In mixed stands silvicultural removals or severe loss of one species may be compensated for by accelerated growth of the remaining species.