Nectar values from: Quantifying nectar production by flowering plants in urban and rural landscapes

Floral resources (nectar and pollen) provide food for insect pollinators
but have declined in the countryside due to land use change. Given
widespread pollinator loss, it is important that we quantify their food
supply to help develop conservation actions. While nectar resources have
been measured in rural landscapes, equivalent data are lacking for urban
areas, an important knowledge gap as towns and cities often host diverse
pollinator populations. We quantified the nectar supply of urban areas,
farmland and nature reserves in the UK by combining floral abundance and
nectar sugar production data for 536 flowering plant taxa, allowing us to
compare landscape types and assess the spatial distribution of nectar
sugar among land uses within cities. The magnitude of nectar sugar
production did not differ significantly among the three landscapes. In
urban areas the nectar supply was more diverse in origin and predominantly
delivered by non-native flowering plants. Within cities, urban land uses
varied greatly in nectar sugar production. Gardens provided the most
nectar sugar per unit area and 85% of all nectar at a city scale, while
gardens and allotments produced the most diverse supplies of nectar sugar.
Floral abundance, commonly used as a proxy for pollinators’ food supply,
correlated strongly with nectar resources, but left a substantial
proportion of the variation in nectar supply unexplained. Synthesis. We
show that urban areas are hotspots of floral resource diversity rather
than quantity and their nectar supply is underpinned by the contribution
of residential gardens. Individual gardeners have an important role to
play in pollinator conservation as ornamental plants, usually non-native
in origin, are a key source of nectar in towns and cities.