Effects of Douglas fir on forest biodiversity
Under climate change, forestry in Switzerland promotes the increased cultivation of exotic Douglas fir (Pseudotsuga menziesii), as Douglas fir is more drought-resistant than native spruce. However, nature conservation organisations fear that enhanced planting of Douglas fir will negatively affect biodiversity and that Douglas fir has invasive potential. Based on the existing scientific and grey literature, we compile the present knowledge on the effects on forest habitats and biodiversity and the invasiveness of Douglas fir in Central Europe. The cultivation of Douglas fir does not seem to have any additional negative effects on soils as compared to native conifers, and its effects on biodiversity are diverse and often inconsistent. Overall, there is often a shift in species composition and in the dominance ratio for most studied groups of organisms (e.g. fungi, plants, arthropods, birds) in Douglas fir stands. Although natural regeneration of Douglas fir does occur in many regions of Central Europe, its extent, site-specificity and frequency and, therefore, the invasiveness of Douglas fir are not yet clear. We identified the following knowledge gaps: 1) Douglas fir should be studied along mixture gradients with other tree species, especially beech, in order to determine threshold values at which negative effects of biodiversity begin to appear. 2) The effects of Douglas fir on Red List, priority or characteristic forest species have not yet been thoroughly evaluated. 3) Frequency of natural regeneration and dispersal potential of Douglas fir in Central Europe should be assessed. Filling these knowledge gaps will allow a more reliable and integral assessment of the biodiversity effects of Douglas fir and its invasive potential.
The systems of managing wildlife and forest in central Europe