Pollen limitation of Vaccinium myrtillus along an elevational gradient

Plant dependence on pollinator-aided reproduction may decrease with colder and more unstable climates, for example at higher elevations. Correspondingly, plant populations may also be more pollen limited in alpine than in lowlands or under more optimal conditions. However, such expectations have largely been investigated across species, and rarely among populations within a species. The findings of such studies may have implications for predictions of plant sexual reproduction in a changing climate. We combined a bagging experiment of Vaccinium myrtillus (bilberry) flowers with a supplemental pollen experiment at three sites along an elevational gradient at 100, 500 and 900 m a.s.l. in a mild boreal climate, by the Sognefjord, Norway. Our goal was to investigate the variation in reproductive success and pollen limitation in a functionally important plant species, V. myrtillus, and to test whether the outcomes may be dependent on insect flower visitation and climatic context (i.e. temperature related to elevation). Our experimental treatments clearly affected reproductive success of V. myrtillus. Bagging of flowers reduced the fruit set close to zero, whereas supplemental pollination resulted in 30% higher fruit set. However, fruit set effects appeared to be independent of elevation in the current study. Total number of seeds was highest at the optimal mid-site location, but here the proportion of mature seeds was also lowest. Our results clearly showed that the reproductive success of V. myrtillus depends on pollinator visitation and benefits from extra pollen supply, but that these effects appeared to be independent of the climatic context.