Turnover in floral composition explains species diversity and temporal stability in the nectar supply of urban residential gardens

Tew, Nicholas E., Baldock, Katherine, Vaughan, Ian P., Bird, Stephanie and Memmott, Jane (2021) Turnover in floral composition explains species diversity and temporal stability in the nectar supply of urban residential gardens. Journal of Applied Ecology. ISSN 0021-8901 (In Press)

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1. Residential gardens are a valuable habitat for insect pollinators worldwide, but differences in individual gardening practices substantially affect their floral composition. It is important to understand how the floral resource supply of gardens varies in both space and time so we can develop evidence-based management recommendations to support pollinator conservation in towns and cities. 2. We surveyed residential gardens in the city of Bristol, UK, at monthly intervals from March to October. For each of 472 garden surveys, we combined floral abundances with nectar sugar data to quantify the nectar production of each garden, investigating the magnitude, temporal stability, and diversity and composition of garden nectar supplies. 3. We found that individual gardens differ markedly in the quantity of nectar sugar they supply (from 2 g to 1662 g), and nectar production is higher in more affluent neighbourhoods, but not in larger gardens. Nectar supply peaks in July (mid-summer), when more plant taxa are in flower, but temporal patterns vary among individual gardens. At larger spatial scales, temporal variability averages out through the portfolio effect, meaning insect pollinators foraging across many gardens in urban landscapes have access to a relatively stable and continuous supply of nectar through the year. 4. Turnover in species composition among gardens leads to an extremely high overall plant richness, with 636 taxa recorded flowering. The nectar supply is dominated by non-natives, which provide 91 of all nectar sugar, while shrubs are the main plant life form contributing to nectar production (58). Two thirds of nectar sugar is only available to relatively specialised pollinators, leaving just one third that is accessible to all. 5. Synthesis and applications. Our study demonstrates that pollinator-friendly management, affecting garden quality, is more important than the size of a garden, giving every gardener an opportunity to contribute to pollinator conservation in urban areas. For gardeners interested in increasing the value of their land to foraging pollinators we recommend planting nectar-rich shrubs with complementary flowering periods and prioritising flowers with an open structure in late summer and autumn.

Item Type: Article
Additional Information: Funding information: This work was supported by the Natural Environment Research Council through the NERC GW4+ Doctoral Training Partnership (NE/L002434/1) and by the Royal Horticultural Society. We thank the members of the public who gave us permission to survey their gardens, field assistant Joanne Morten for help quantifying the nectar production of plants in the field and Mathilde Baude for methodological advice and data sharing.
Uncontrolled Keywords: Floral resources, Flowering phenology, Gardens, Landscape, Nectar, Pollinators, Pollinator conservation, Urban ecology
Subjects: F800 Physical and Terrestrial Geographical and Environmental Sciences
Department: Faculties > Engineering and Environment > Geography and Environmental Sciences
Depositing User: John Coen
Date Deposited: 05 Nov 2021 14:58
Last Modified: 05 Nov 2021 15:00
URI: http://nrl.northumbria.ac.uk/id/eprint/47651

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