A new study funded by Rowse Honey Ltd, conducted by researchers at the University of Sussex, has shown that weeds are far more valuable in supporting biodiversity than we give them credit for. It compares the biodiversity value of plants classified as 'injurious weeds' to the biodiversity value specified by DEFRA for pollinator-targeted agri-environmental options.
Findings of Research:
The results show that the abundance and diversity of pollinators visiting weed species is far greater than that of DEFRA-recommended plants. Dr. Nicholas Balfour and Professor Francis Ratnieks compared the biodiversity value of plants classified as 'injurious weeds' to the biodiversity value specified by the Department for Environment, Food and Rural Affairs (DEFRA) for pollinator-targeted agri-environmental options such as red clover and wild marjoram.
Their findings, which were published in the Journal of Applied Ecology, show that the abundance and diversity of pollinators visiting weed species are far greater than that of DEFRA-recommended plants.
The 1959 Weeds Act classifies five species of native wildflowers as "injurious" in the United Kingdom. Many species of bees and other insects frequent three of them: ragwort (Jacobaea vulgaris) and two thistles (Cirsium arvense, C. vulgare). The other two are docks (Rumex crispus and R. obtusifolius), which have wind-pollinated flowers.
Dr. Balfour and Professor Ratnieks conducted a field study in East Sussex, where they quantified and identified insects visiting three of these species, which included the flowers of ragwort, thistles, and other wildflowers, including those recommended by DEFRA, growing in six pasture or ex-pasture sites.
Their findings, which revealed that pollinators visited weed species in greater numbers than DEFRA-recommended plants, were corroborated by a subsequent review of scientific literature.
The three insect-pollinated weeds have been visited by four times as many pollinator species and five times as many conservation-listed species, according to the Database of Pollinator Interactions. Weeds ranked fourth (C. arvense), sixth (J. vulgaris), and thirteenth (out of 387 plant species examined in the database) in terms of pollinator species recorded (C. vulgare). Similarly, the Database of Insects and their Food Plantsshowed that twice as many herbivorous insect species are associated with the five weed species.
"There is now a substantial body of evidence that shows that weeds are a vitally important resource for pollinators," said Dr. Nicholas Balfour, Post-Doctoral Researcher at the Laboratory of Apiculture and Social Insects (LASI) at the University of Sussex.
"The three insect-pollinated species have open flowers that allow access to a wide variety of pollinator species, and they produce four times more nectar sugar on average than the DEFRA recommended plant species."
"Pollinators are critical to the preservation of global biodiversity, ecosystem resilience, and agricultural output." However, there are serious concerns about pollinator declines, and the long-term decline of flowers in our landscapes is regarded as a major contributor.
"We recognize that agricultural weeds can reduce yields in arable and pastureland. However, we've shown that they can be extremely beneficial to both flower-visiting and herbivorous insects, and they shouldn't be overlooked when it comes to preserving our natural biodiversity."
Francis Ratnieks, Professor of Apiculture at the University of Sussex's Laboratory of Apiculture and Social Insects (LASI), stated: "Unfortunately, many common native plant species that are important for wildlife conservation are underappreciated. The importance of ragwort and thistles to flower-visiting insects is demonstrated here. LASI has previously demonstrated the importance of bramble and ivy, plants that are frequently referred to negatively, such as thugs or parasites."
(Source: University of Sussex)
