Priority assessment for conversion of Norway spruce forests through introduction of broadleaf species

Abstract

Serious damage to Norway spruce ( Picea abies L. Karst) in Central and Western Europe together with increasing preference for forests with natural species composition emphasise the necessity to convert Norway spruce plantations on unsuitable sites and outside of its natural distribution. Site related priority assessment of Norway spruce replacement by Fagus sylvatica L., Quercus robur L., Acer pseudoplatanus L. and Fraxinus excelsior L., respectively, was calculated using a geographical information system for a management unit of 1248 ha in Upper Austria. Three matrix overlays combining soil depth with soil skeleton and vegetation type with gleyification resulted in different risk categories for Norway spruce. Further matrix overlay with Norway spruce stocking indicated sites with high conversion priority. Suitability indices of broadleaf species were evaluated using indexing overlay, allowing to weight map attributes of seven site parameters. This calculation was done separately for each species studied. Combination of these suitability indices with the conversion priority of Norway spruce led to site-related introduction priorities. The largest areas were found for Q. robur, followed by F. sylvatica. The higher suitability of Q. robur compared to F. sylvatica was explained by its superior adaptation to the acidic, shallow and partially gleyic soils in the area. The introduction of F. excelsior was generally not found advisable. The advantage of this method over the use of classic site classification was seen in the direct implementation of current stand characteristics into the decision rules.