The first Britain-wide assessment of the value of wild flowers as food for pollinators shows that decreasing resources mirror the decline of pollinating insects.
The study, by researchers at the University of Leeds and University of Bristol supported by the Centre for Ecology and Hydrology and Fera Science Ltd, combines vegetation surveys taken over the last 80 years with modern-day measurements of nectar to provide the most comprehensive assessment ever published.
An article published in the journal Nature today provides new evidence to support the link between plant and pollinator decline.
It reports substantial losses to nectar resources in England and Wales between the 1930s and 1970s – a period closely linked with agricultural intensification.
By 1978, the researchers discovered that nectar resources had stabilised and actually increased from 2000. The findings fit nicely with a similar pattern in recent pollinator trends: two recent papers have suggested that declines in pollinator diversity in the mid-20th Century slowed down or partially reversed over recent decades.
Professor Bill Kunin, Professor of Ecology in the University of Leeds’ Faculty of Biological Sciences, said: “Wild bees and other insect pollinators are vital to the success of many important food crops and wild plants. It is therefore really important that we understand the relationships between floral resources and pollinating insect populations. Despite the stabilisation seen recently, our research shows significant long-term declines in the diversity of nectar sources mirrored in a fall in the diversity of pollinator species. We are at a point where only four plant species account for more than half the nectar in Britain.”
Professor Jane Memmott, Professor of Ecology at the University of Bristol, said: “Over the last few decades despite stabilisation, the diversity of nectar sources has declined – a trend seemingly mirrored in the diversity of pollinator species.”
The study also looked at the type of habitats most beneficial for pollinators, highlighting arable land as the poorest source of nectar: both in terms of amount and the diversity of sources. Improved grasslands could however contribute the most to national nectar supply if management favoured greater flowering of plants such as white clover.
Lead author Dr Mathilde Baude said: “Nationally, a small number of plants contribute massively to nectar provision including clover, heather and thistles. These very common species are very important to ecosystem functioning, yet they are often disregarded.”
Professor Kunin added: “Farmers on Agri-environment schemes can plant wild flowers to help improve the value of their land for pollinators, but the areas involved have been small and thus the contribution to floral resources at the national scale is still low. On the other hand, there are vast areas of improved grasslands, and small changes in management to increase wild flowers could make a huge contribution nationally.”
This study provides new evidence for policy makers to help restore national nectar supplies for our important insect pollinators.
The Insect Pollinators Initiative is joint-funded by the Biotechnology and Biological Sciences Research Council (BBSRC), Defra, the Natural Environment Research Council (NERC), the Scottish Government and the Wellcome Trust. It is managed under the auspices of the Living with Environmental Change (LWEC) partnership.
Image information: The bag placed over the bell heather's flowers excluded pollinators, allowing researchers to collect nectar over 24 hours. Photograph credit: Dr Mathilde Baude.
Further information: Contact Chris Bunting, Senior Press Officer, University of Leeds, at 0113 343 2049 or c.j.bunting@leeds.ac.uk
The full paper: Mathilde Baude et al., "Historical nectar assessment reveals the fall and rise of Britain in bloom," is published in Nature (DOI: 10.1038/nature16532)