Data from: Phenology of farmland floral resources reveals seasonal gaps in nectar availability for bumblebees

Floral resources are known to be important in regulating wild pollinator
populations and are therefore an important component of agri‐environment
and restoration schemes which aim to support pollinators and their
associated services. However, the phenology of floral resources is often
overlooked in these schemes – a factor which may be limiting their
success. Our study characterises and quantifies the phenology of nectar
resources at the whole‐farm scale on replicate farms in Southwestern UK
throughout the flowering season. We quantify the corresponding nectar
demands of a subset of common wild pollinators (bumblebees) to compare
nectar supply and pollinator demand throughout the year, thereby
identifying periods of supply‐demand deficit. We record strong seasonal
fluctuations in farmland nectar supplies, with two main peaks of nectar
production (May and July) and a considerable ‘June Gap’ in‐between. March
and August/September are also periods of low nectar availability.
Comparing the phenology of nectar supply with the phenology of bumblebee
nectar demand reveals ‘hunger gaps’ during March and much of
August/September when supply is unlikely to meet demand. Permanent pasture
and woodland produced the greatest share of farmland nectar because of
their large area, however linear features such as hedgerows and field
margins provided the greatest nectar per unit area. 50% of total nectar
was supplied by just three species (Allium ursinum, Cirsium arvense and
Trifolium repens), but some less productive species (e.g. Hedera helix and
Taraxacum agg.) were important in ensuring phenological continuity of
nectar supply. Synthesis and applications. By comparing the phenology of
farmland nectar supply with the phenology of pollinator demand, we
demonstrate that the timing of nectar supply may be as important as total
nectar production in limiting farmland pollinator populations. Considering
phenology in the design of agri‐environment or restoration schemes is
therefore likely to improve their suitability for pollinators. Plant
species which flower during periods of resource deficit (early spring and
late summer) should be prioritised in schemes which aim to conserve or
restore pollinator populations. Maintaining a range of semi‐natural
habitats with complementary flowering phenologies (e.g. woodland,
hedgerows and field‐margins) will ensure a more continuous supply of
nectar on farmland, thereby supporting pollinators for their entire flight
season.