There is considerable concern over declines in insect pollinator communities and potential impacts on the pollination of crops and wildflowers1,2,3,4. Among the multiple pressures facing pollinators2,3,4, decreasing floral resources due to habitat loss and degradation has been suggested as a key contributing factor2,3,4,5,6,7,8. However, a lack of quantitative data has hampered testing for historical changes in floral resources. Here we show that overall floral rewards can be estimated at a national scale by combining vegetation surveys and direct nectar measurements. We find evidence for substantial losses in nectar resources in England and Wales between the 1930s and 1970s; however, total nectar provision in Great Britain as a whole had stabilized by 1978, and increased from 1998 to 2007. These findings concur with trends in pollinator diversity, which declined in the mid-twentieth century9 but stabilized more recently10. The diversity of nectar sources declined from 1978 to 1990 and thereafter in some habitats, with four plant species accounting for over 50% of national nectar provision in 2007. Calcareous grassland, broadleaved woodland and neutral grassland are the habitats that produce the greatest amount of nectar per unit area from the most diverse sources, whereas arable land is the poorest with respect to amount of nectar per unit area and diversity of nectar sources. Although agri-environment schemes add resources to arable landscapes, their national contribution is low. Owing to their large area, improved grasslands could add substantially to national nectar provision if they were managed to increase floral resource provision. This national-scale assessment of floral resource provision affords new insights into the links between plant and pollinator declines, and offers considerable opportunities for conservation.
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This research was supported by the UK Insect Pollinators Initiative (IPI) ‘AgriLand: Linking agriculture and land use change to pollinator populations’ project, funded by the Biotechnology and Biological Sciences Research Council (BBSRC), Wellcome Trust, Scottish Government, Department of Environment, Food and Rural Affairs (DEFRA) and Natural Environment Research Council (NERC) under the auspices of the Living with Environmental Change partnership: grant BB/H014934/1 (http://www.agriland.leeds.ac.uk). Land Cover and Countryside Survey data are owned by NERC – Centre for Ecology & Hydrology (http://www.countrysidesurvey.org.uk).
Extended data figures
Extended data tables
This file contains Supplementary Table 11, which shows plant traits, flowering phenology, flower density, nectar productivity at the flower scale and nectar sugar productivity at the vegetative scale for the list of 260 species.
This table contains a reference list for flower-visiting insects of the four main nectar providers nationally. It lists sources and data used to investigate the visiting insects of the main nectar providing plant species (Extended Data Table 2). This combines published and unpublished plant-pollinator interactions data from Memmott’s group and a review of literature of insect species visiting flowers of Trifolium repens, Calluna vulgaris, Cirsium palutre and Erica cinerea.
This table contains a reference list for published sugar potential values in kg/ha /year. It lists sources and data used to compare our nectar values (in kg/ha cover/year) to those found in literature (Extended Data Figure 6g). Published values of sugar potential are available for 128 species at the time of writing. Where values were available from more than one source, an average was calculated. Where values were given only as honey potential in the literature, these values were multiplied by 0.8 to give sugar potential. This ratio has been reported in the majority of the published sources (References 1, 5-17).