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.

Data: floral abundance, and nectar production scaled to site level

[N.B. See 'Related Works' for data on nectar production of individual plant taxa (available from 01 August 2022)]

Floral_abundance.xlsx - floral counts obtained by quadrat sampling (conducted by Baldock et al. 2015, 2019).

• Tab 1 = ‘Q1_Three_landscapes’ - number of floral units of each taxon recorded in urban, farmland and nature reserve landscapes, with rows representing a single occurrence of a plant taxon in a quadrat (3701 rows).​​​​
• Tab 2 = ‘Q2_Nine_land_uses’ - number of floral units of each taxon recorded in nine urban land uses, with rows representing a single occurrence of a plant taxon in a quadrat (16888 rows).

Site-level_Q1_Three_landscapes.xslx - pooled site-level nectar mass and diversity values for the comparison of urban, farmland and nature reserve landscapes.

• Tab 1 = ‘All_plants’ - nectar sugar mass and floral abundance (number of floral units) per sampling site for all plants (36 sites).
• Tab 2 = ‘Native_plants’ - nectar sugar mass and floral abundance (number of floral units) per sampling site for native plants (36 sites).
• Tab 3 = ‘Non-native_plants’ - nectar sugar mass and floral abundance (number of floral units) per sampling site for non-native plants (36 sites).
• Tab 4 = ‘Diversity_index’ - nectar source diversity (Shannon index) per sampling site for all plants (36 sites).

Site-level_Q2_Nine_land_uses.xlsx - pooled site-level nectar mass and diversity values for the comparison of nine urban land uses.

• Tab 1 = ‘All_plants’ - nectar sugar mass and floral abundance (number of floral units) per sampling site for all plants (360 sites).
• Tab 2 = ‘Native_plants’ - nectar sugar mass and floral abundance (number of floral units) per sampling site for native plants (360 sites).
• Tab 3 = ‘Non-native_plants’ - nectar sugar mass and floral abundance (number of floral units) per sampling site for non-native plants (360 sites).
• Tab 4 = ‘Diversity_index’ - nectar source diversity (Shannon index) per sampling site for all plants (360 sites).