Response of bilberry (Vaccinium myrtillus) to clear-cutting and single-tree selection harvests in uneven-aged boreal Picea abies forests

The aim was to analyse the short-term effects (0-4 years) of selection fellings and clear-cutting on bilberry (Vaccinium myrtillus), one of the dominant field layer plants in the Swedish boreal coniferous forests. Bilberry is a major source of food for many herbivores. The effects of forest harvesting were studied on bilberry characteristics of potential importance for herbivores. Five characters of bilberry growth (vegetative investment, shoot survival, ground cover, shoot weight and production of current annual shoots), two of reproduction (reproductive investment and success) and four of chemical composition (water, nitrogen, carbon and phenol content) were measured. Sunlight reaching the field layer was also measured. Significantly more sunlight reached the field layer, while vegetative investment and shoot survival of bilberry were significantly lower in clear-cuttings than in selective fellings and uncut controls. Ground cover of bilberry was significantly higher in control forests than in selection fellings and clear-cuttings. Production of current shoots are significantly higher in uncut controls than in clear-cuttings. Water content was significantly lower, while carbon and phenol content was significantly higher in bilberry shoots growing in clear-cuttings than in uncut controls. Nitrogen content, reproductive investment and reproductive success were not affected by the different practices. Bilberry was severely affected by clear-cutting. Low vegetative investment, shoot survival, ground cover and production of current annual shoots suggests a poor performance of bilberry following clear-cutting. Thus, in clear-cuttings, herbivores feeding on bilberry have a lower amount of shoots available to them and, as indicated by the increased phenol content, the quality of the bilberry also may be reduced. In selection fellings, bilberry ground cover was reduced and spatial distribution was more patchy than in controls. However, vegetative investment and shoot survival of bilberry in selection fellings did not differ from uncut control, but were significantly higher than in clear-cuttings. In contrast to clear-cuttings, phenol content of bilberry shoots did not increase following selection felling. Therefore, over the 4-year term of our study, selection felling seems to provide herbivores with a bilberry vegetation similar to that of the uncut controls. Our results suggest that selective felling, compared with clear-cutting, results in a bilberry field layer of higher availability and quality, which might influence the ecology of many herbivores in the boreal coniferous habitats.