Pollen food resources to help pollinators. A study of five Ranunculaceae species in urban forest

The degradation and scarcity of floral resources represent one of the greatest threats to pollinators on a global scale. In a 2-year study, we aimed to assess the food resources in five members of Ranuculaceae family (Hepatica nobilis Mill., Anemone nemorosa L., A. ranunculoides L., Ranunculus cassubicus L., R. lanuginosus L.), which are common to the ground layer of the deciduous forest habitat in the temperate climatic zone and grow in oak-limehornbeam forest. We assessed the blooming phenology, quantified the amount of nectar and pollen produced in flowers and per unit area, and the proportion and abundance of insect visitors foraging on flowers. The flowers of the analyzed species are multi-staminate and produce pollen but almost no nectar (< 0.05 mg in ca. 20 % of A. nemorosa and A. ranunculoides flowers). The amount of pollen in the flowers differed significantly among the species and years of study. The flowers produced on average 0.64 mg (H. nobilis) ? 2.92 mg (R. lanuginosus) of pollen. The pollen yield per unit area was 0.12?1.36 g/m2 (R. cassubicus ? A. nemorosa, respectively). The protein content in the pollen was 13.2 % (H. nobilis) ? 25.3 % (A. nemorosa), on average. A broad spectrum of pollinators from six taxonomic groups foraging on the Ranunculaceae species was identified, with the great majority of honeybees and bumblebees (41.6 % and 29.5 % of the total individuals noted, respectively). The Ranunculaceae species are potentially suitable to fulfill the hunger gap for pollinators between approx. mid-March and the first decade of May and should be considered in development of strategic conservation protocols to preserve or restore foraging habitats supporting healthy pollinator populations.

Automated summary

The study revealed that Ranunculaceae species in oak-limehornbeam forests in temperate climates are important food resources for pollinators, with rich pollen and protein content in their flowers attracting a variety of pollinators for foraging, especially honeybees and bumblebees.