Weeds valuable to pollinators and biodiversity

The so called ‘injurious’ weeds are actually more valuable to pollinators and biodiversity than previously thought and now researchers are calling policymakers to take another look at how existing policies are implemented and reconsider the role of weeds in future agri-environmental policy.

The study by researchers in the UK at the University of Sussex found that weeds are far more valuable in supporting biodiversity than we give them credit for. Published in the Journal of Applied Ecology, the study puts forward evidence that show that the abundance and diversity of pollinators visiting weed species are far higher than Department for Environment, Food and Rural Affairs (DEFRA) recommended plants.

According to researchers, five species of native wildflowers are classified as “injurious” in the 1959 Weeds Act. Three of them are frequently visited by many species of bees and other insects – ragwort (Jacobaea vulgaris) and two thistles (Cirsium arvense, C. vulgare). The other two are docks (Rumex crispus and R. obtusifolius), whose flowers are mainly wind-pollinated.

Field studies were carried out in East Sussex where researchers quantified and identified insects visiting three of these species – the flowers of ragwort, thistles, and other wildflowers, including those recommended by DEFRA – growing in six pasture or ex-pasture sites.

Their results, which found that pollinators were visiting weed species in higher numbers than DEFRA recommended plants, were mirrored by a subsequent analysis of scientific literature.

In the Database of Pollinator Interactions, four times as many pollinator species and five times more conservation-listed species have been recorded visiting the three insect-pollinated weeds. Of the 387 plant species analysed in the database, in terms of pollinator species recorded, the weeds were ranked 4th (C. arvense), 6th (J. vulgaris), and 13th (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.