Long and short term effects of stump harvesting on saproxylic beetles and ground flora

摘要

Research on the effects from forest management on biodiversity has been going on for decades but still there are many questions unanswered. With every introduction of a new forestry method there is risk for increased pressure on biodiversity.ud The harvesting of low stumps left after final harvesting is a relatively new method used in forestry. I therefore investigated the importance of low stumps for saproxylic (wood living) species by comparing the species richness, abundance, and species assemblages of beetles in low stumps with the levels in high stumps and logs. Furthermore, I also investigated the long-term effects from stump harvesting on this group of species. I used window traps to collect beetles in young forests that had been stump harvested 25 years prior to the study and compared these stands with stands of the same age that had not been stump harvested. I also wanted to investigate the short-term effects from stump harvesting on the ground flora. This was done by comparing the plot frequency of all bryophytes and vascular plants found on stump harvested clear-cuts with clear-cuts that had not been stump harvested.ud Low stumps on clear-cuts were proved to constitute important habitat for wood living beetles and they produced as many species and individuals of saproxylic beetles as logs and high stumps. Individual species showed preference for certain substrates. For example, the saproxylic fungivore Enicmus rugosus, was mostly found on low stumps. The overall impression after comparing the three substrate types was that low stumps might be an underestimated source of habitat for wood living insects. The long-term experiment indicated that effects of stump harvesting may last two and a half decades on certain groups of beetles. However, the effects from the surrounding landscape explained the patterns in beetle occurrence better than stump harvesting did. Results from the study of short-term effects on the ground flora showed that the effects from stump harvesting were limited to common species of bryophytes and vascular plants. The plot frequency of the common dwarf shrub Vaccinium vitis-idaea was, nevertheless 80% lower on the stump harvested clear-cuts, indicating that the early response of stump harvesting may be strong on individual species.