Effects of plant community composition and flowering phenology on honeybee foraging in Mediterranean sylvo-pastoral systems

Questions: Which are the most effective plant communities for honeybee foraging
and honey production in Mediterranean sylvo-pastoral systems? What is
the relationship between flowering phenology and pollen occurring in honey
sediments?
Location: Mediterranean sylvo-pastoral systemin Gallura, Sardinia, Italy.
Methods: Phytosociological and phenological surveys were performed in a circular
area of 1.5 km radius with a small apiary placed in the centre. Polleniferous
and nectariferous values of plant communities were assessed based on the cover
and the polleniferous and nectariferous value of each constituting species.
Honey production was quantified during the main flow (March–June) and
subjected to melissopalynological analysis. Data were evaluated by ordination
through principal components analysis and principal coordinates analysis. The
latter utilized a new index, developed for calculating the phenological distances
based on the individual distributions of flowering frequencies.
Results: Plant communities richest in species providing pollen and nectar were
Rhamnus hedges. There was a close correlation between polleniferous and nectariferous
values, suggesting that plant communities are important for honeybee
foraging of both resources. The temporal flowering sequence ensured the supply
of nectar and pollen throughout the spring season. Pollen foraged from 12 Trifolium
species with different flowering phenology was the most abundant. Salix
purpurea and Rhamnus alaternus were productive at the beginning of the season,
followed by Lavandula stoechas, Echium plantagineum and E. italicum.
Conclusions: Plant communities vary in importance for honeybee foraging
mainly due to differences in floristic composition and flowering phenology.
Communities characterized by human presence (e.g. semi-natural grasslands
and hedges) are the most relevant. Some target species (e.g. Trifolium spp.)
favoured by grazing livestock ensure foraging for honeybees throughout the season.
Plant communities of wild areas, such as the garrigue vegetation, provide
foraging for unifloral valuable honey (i.e. ‘Lavandula’ honey).