Saproxylic insect fauna in stumps on wet and dry soil: implications for stump harvest. (Special Issue: Environmental effects of tree-stump harvesting.)

摘要

An increasing demand for bioenergy has stimulated interest in harvesting of tree stumps after felling operations. To reduce the amount of soil disturbance, it is recommended to retain stumps in wet areas. We wanted to evaluate if that strategy is beneficial also for saproxylic (wood-living) insects, which will have less habitat to breed in at stump harvest, and therefore also need mitigation. We tested if stumps in wet positions on a clear-cut harbour fewer species and a different assemblage of saproxylic insects than do stumps in dry positions. Insects were reared out from wood pieces taken from 100 stumps (50 Norway spruce, Picea abies and 50 birch, Betula spp.) sampled in pairs: one stump from wet and one from dry soil in each pair. In the lab 2201 individuals representing 49 beetle and 6 moth species were encountered. Fewer species were found in spruce stumps on wet soil than on dry soil, both when measured per stump or as an accumulated value over all stumps within the categories. No difference was detected between the number of species found in wet and dry birch stumps. However, three beetle species that live mainly in birch were more common in dry stumps than in wet. No species showed an association with wet stumps. We conclude that stumps in wet positions form an inferior habitat to stumps in dry positions, and that this should be considered when making recommendations concerning the harvesting of stumps for bioenergy.