Is salvage logging a proper tool for restoration of forest ecosystems affected by bark beetle outbreak?

Abstract

Is salvage logging on deciduous forest habitats essential in restoration of forest ecosystems affected by bark beetle outbreak?

Biotic and abiotic disturbances are part of the life cycle of natural forests. They increase the structural and biotic diversity of forests ecosystems. Norway-spruce dominated stands of Central Europe are often affected by outbreaks of Ips typographus, which initiate "stand replacement" pathways of forest regeneration (sensu Veblen 1992). Such processes are difficult to accept from the point of view of forestry. Thus, in forest stands disturbed by the insect outbreaks, salvage logging and tree replanting are usually implemented, while natural processes leading to forest regeneration play the minor role.

We studied two different aspects of forest ecosystem recovery in salvage logged and in unmanaged (not logged) spruce-dominated forests affected by spruce bark beetle: (1) tree regeneration dynamics in the lower mountain zone of the Beskidy Mts. (Silesian Beskids, S Poland), and (2) changes in herb layer composition in the lowlands, in the Białowieża Forest (N-E Poland). Both, in mountains and lowlands, the ratio of spruce in the studied stands was artificially high (50-90% and 20-80%, respectively) due to former rejuvenation planting on sites of broadleaved forests. Otherwise, deciduous trees would naturally dominate in these forest habitats: beech in the mountains and oak, lime and hornbeam in the lowlands. In the mountainous zone we investigated the sites where all dead trees were removed with no successive tree replanting (the reference stands where no trees were logged were not available). Natural tree regeneration process was very dynamic and led to re-establishment of beech-dominated stands. In the lowlands the total species richness of the herb layer was significantly higher in sites with removed dead trees and trees replanted. However, an increase was mainly due to appearance of species characteristic of non-forest, open habitats. Such trends were not observed in sites with untreated sites with standing dead spruce. In contrast, compared to salvage-logged sites, ancient woodland species, typical to mixed deciduous forest maintained higher abundance in unmanaged stands, where salvage logging did not take place. Both forest types studied revealed great potential for natural reestablishment of species composition typical to deciduous forests. Thus, from the conservation point of view post-disturbance salvage logging is needed neither for recovery of beech in the mountain deciduous forests nor for recovery of herb layer of mixed-deciduous forests in the lowlands. Furthermore, in the case of lowland forests investigated such treatements inhibit the spontaneous recovery of herb layer species composition typical to broadleaved forests.

Veblen T.T. 1992. Regeneration dynamics,in: Plant succession: theory and prediction (eds. D.C. Glenn-Lewin, R.K. Peet, T.T. Veblen). Chapman and Hall, London, 152-187.