Plant-pollinator interactions along an elevational gradient in Central European forest understorey

Abstract

Elevational gradients provide a framework for understanding how environmental filtering reorganises communities and interactions, but plant-pollinator interactions along temperate forest elevational gradients remain overlooked. We studied early-spring understorey communities at four forest sites spanning the foothills towards the timberline (450-1,000 m a.s.l.) in the Krkono[s]e Mountains, Czechia. Across six transects per elevation, we quantified flowering plant species richness, floral resources and traits, and video-recorded flowers, yielding 4,003 pollinator visits. We analysed elevational patterns in species richness, community composition, floral traits, and quantitative network characteristics. Visitation frequency and flowering plant and pollinator species richness peaked at intermediate elevations. The contribution of dipteran relative to hymenopteran pollinators increased towards higher elevations, principally because of non-hoverfly flies, whereas individual bee groups showed no uniform response. Floral resources and traits showed no uniform elevational responses, although total nectar sugar availability peaked at the highest site because of the dominant Vaccinium myrtillus. Most notably, both network-level specialisation and mean species-level specialisation were generally greater at the two higher elevations, whereas nestedness was lower and other network characteristics showed no consistent patterns. These findings suggest that shifts in pollinator composition and dominant floral resources potentially shaped interactions along the gradient. The increasing specialisation with elevation contrasts with the generalisation often expected under reduced partner availability and indicates that forest networks may follow elevational patterns not predicted from open habitats. Despite limited site-level replication, this study provides, to our knowledge, the first community-wide characterisation of plant-pollinator interactions along a temperate forest elevational gradient and identifies patterns requiring evaluation across replicated gradients.