Ola Atlegrim

Exclusion of birds from bilberry stands: impact on insect larval density and damage to the bilberry

SummaryThe bilberry (Vaccinium myrtillus L.), is the dominant plant in the field layer of many boreal forests in northern Sweden. It is utilized by several herbivorous insect larvae as food (i.e. Lepidoptera: Geometridae, Tortricidae and Hymenoptera: Symphyta). Total density of insect larvae was 63% lower where birds had access to larvae compared to exclosures. Larvae with a feeding behaviour which exposes them to birds (geometrids and sawflies) showed a pronounced reduction in density when exposed to bird predators. Density of larvae with a concealed feeding behaviour (tortricids) was unaffected by birds. The frequency of larval damage to bilberry annual shoots was significantly higher in areas where larval density was high due to exclusion of birds. I concluded that birds have the potential to heavily modify the interaction between bilberry and insect larvae.

Effects of management on coarse woody debris volume and composition in boreal forests in northern Sweden

Forest management practices have led to a reduction in the volume and a change in the composition of coarse woody debris (CWD) in many forest types. This study compared CWD volume and composition in reserves and two types of managed forest in the central boreal zone of Sweden. Ten areas were surveyed, each containing clear-cut, mature managed and old-growth stands, to determine the volume of standing and lying CWD in terms of species composition, decay class and size class. Volumes of CWD on clear-cuts and in mature managed forests were high compared with previous studies. Old-growth forests (72.6 m3 ha−1) contained a greater volume of CWD than mature managed forests (23.3 m3 ha−1) and clear-cuts (13.6 m3 ha−1). Differences were greatest for the larger size classes and intermediate decay stages. Despite stand ages being up to 144 years, CWD volume and composition in managed forests was more similar to clear-cuts than to old-growth forests.

Effects of clear-cutting and single-tree selection harvests on herbivorous insect larvae feeding on bilberry (Vaccinium myrtillus) in uneven-aged boreal Picea abies forests

Abstract In uneven-aged boreal Picea abies forests in north-eastern Sweden, the effects of clear-cutting and single-tree selection on herbivorous insect larvae feeding on bilberry (Vaccinium myrtillus) were studied. Abundance of geometrids and exposed folivorous larvae were significantly lower in clear-cut areas than in selection felled and uncut controls. Significantly lower total abundance of herbivorous larvae were found in clear-cuttings compared to uncut controls. Both stem and leaf damage were significantly higher in selection fellings and controls than in clear-cuttings. The dry biomass consumption per shoot and per larva were significantly higher in selection fellings and uncut controls than in clear-cuttings. Lower availability and quality of bilberry may explain the reduced abundance of larvae and the reduced consumption of bilberry by larvae in clear-cuttings. The entire tree layer is removed when the forest is clear-cut, and drastic changes in abiotic factors are probably the ultimate reason for the observed responses of both bilberry and larvae. Selection felling leaves an intact, although sparser, tree layer following harvest, and abiotic factors are probably only moderately affected. The moderate changes of abiotic factors are probably the reason for small effects on both bilberry and larvae by selection felling. Our results suggest that clear-cutting negatively affects bilberry, herbivorous larvae feeding on bilberry, and their interaction. Contrary to the negative effects of clear-cutting, bilberry, insect larvae and their interaction in selection felling seems to resemble that in uncut forest. Because exposed larvae feeding on bilberry are known to be an important food commonly used by birds during their breeding, it could be of significance that forest harvesting has only moderate effects on bilberry and larvae.

Selective felling as a potential tool for maintaining biodiversity in managed forests

In Sweden one forestry method, the clear-cutting method, has been used all over the country despite differences in climate, topography etc. At present there is a growing interest in using alternative methods such as selective felling, which to a larger extent mimic natural disturbances. In this study we compare virgin forests with stands which have been cut with old selective felling (dimension felling), new selective felling (single tree selection felling), and clear-cutting with respect to frequency of characters important to biodiversity (mainly dead wood). The frequency of different types of dead wood decreases with increasing intensity of the cutting method in the following order: old selective felling, new selective felling, and clear-cutting. New selective felling had higher amounts and quality of dead wood compared to clear-cutting. New selective felling also showed less differences compared to virgin forests than clear-cutting. Dead wood in new selective felling compared to clear-cutting may offer substrate for different types of faunas because of the environment surrounding the dead wood. Even if the new selective felling method seems to provide higher amounts of dead wood compared to the clear-cutting method, further studies of organisms utilising the dead wood are needed. New selective felling does not seem to solve the problem of decreasing availability of dead wood in managed forests and there is still a need to preserve unmanaged forest patches in a landscape perspective in order to offer habitats with a high amount of dead wood.

Lepidoptera larvae as food for capercaillie chick (tetrao urogallus): A field experiment

Lepidoptera larvae are important prey for capercaillie chicks {Tetrao urogallus), but utilization varies among habitats. This field experiment investigates the effects of larval feeding behaviour, abundance and the density of bilberry (Vacciniwn myrtillus) on utilization of larvae by a group of four capercaille chicks and also tests whether chick utilization differs between wet and dry coniferous forest. In fenced plots, four hand‐raised chicks were released for a 15 min feeding period. Reduction of geometrid larvae was correlated positively with their abundance but correlated negatively with bilberry density. Geometrids had a much higher predation risk than pyralids and tortricids, probably because they are exposed while feeding, in contrast to pyralids and tortricids. Total reduction of lepidoptera was higher in wet than dry forest, probably due to a higher proportion of geometrid larvae, and lower density of bilberry in the wet forest. The manner of insect feeding and habitat type (e.g. wet and dry for...