Management of transformation in central Europe

Abstract

The historical background, the management practice, growth and yield aspects of transformation of artificial coniferous stands in central Europe are outlined. Past management has reduced the proportion of natural broad-leaved forests from 66 to 33% of the forest area. The pure stands of planted Norway spruce ( Picea abies) and Scots pine ( Pinus sylvestris) show increased instability and susceptibility to damage by snow and wind. Proposals for transformation go back to the nineteenth century, but the diversity of sites, stand structures and different goals of owners make transformation a variable task. This paper outlines three case studies of transformation and some results of growth research into transforming coniferous stands, based on the situation in south-western Germany which is comparable to other parts of central Europe. The first case study deals with two experimental stands in the southern Black Forest which have been developed from an even- to an uneven-aged structure. Diameter distribution, residual volumes, harvesting results and periodic increments and yields are characterised. The second case study outlines the transformation of pure Norway spruce stands. On stable sites, an uneven-aged mosaic structure with 20–40% beech can be reached by crop-tree oriented thinning from above, target-diameter harvesting, natural regeneration and underplanting of beech if needed. On unstable sites, transformation will be realised either by clearfelling and seeding, conversion to oak by planting or by underplanting of silver fir and single-tree harvesting. The third case study deals with pure Scots pine stands: natural regeneration of Scots pine allows transformation options either rather fast in combination with clearfelling and/or seeding, or delayed with lasting regeneration procedures, or as nearly continuous cover system with low density of overstorey. Some growth and yield problems in transforming coniferous stands are shown using the example of the “Langenbrand-experiment”, started in 1927 in the northern Black Forest. There are effects of differing regeneration periods on growth rates caused by the interaction between the old and the young stands. These have an influence on the growth reactions of the residual trees, their mortality and the pattern of height/diameter ( h/ d) ratios in the natural regeneration. The h/ d relationships of the young stands depend on the length of the regeneration period with longer periods promoting more favourable ratios which should positively influence the stability of future stands.