Digestibility and N-concentration of bilberry shoots in relation to berry production and N-fertilization

Abstract

This study aims to assess relationships between berry production, digestibility and nitrogen (N) availability in the ericaceous dwarf shrub ( Vaccinium myrtillus), which is a key-stone species in spruce forests across northern Eurasia. The study is based on a combination of monitoring and experimental approaches. First, we measured berry production, in vitro dry matter digestibility and N-concentration of bilberry shoots collected in autumn during a 10-year period from 10 different sites in southern Norway. Second, N-fertilization and flower removal experiments were performed during a three-year period at one site. The annual levels in digestibility and N-concentration of bilberry shoots were significantly correlated only for the period 2000–2006, when both were positively related to mean berry production. In the experimental plots, only the N-concentration was affected by the treatments. It increased with fertilization and flower removal. For plots that produced berries, N-concentration decreased with berry production. Much of the annual variation in digestibility and N-concentration could be explained by weather variables that may also affect berry production. Autumn population density of bank vole ( Myodes glareolus) peaked one year after peaks in berry production, but was not correlated with digestibility or N-concentration. We conclude that the correlation found in the time series is due to the impact of some common factors, presumably weather, on both berry production and chemical composition of bilberry shoots.