Wildlife friendly refuges around the edges of farmers’ crops have been credited with slowing biodiversity declines, but new research shows their success ultimately depends on what’s growing next to the field.

The new study by Rothamsted Research shows that conservation areas sited directly adjacent to areas of grassland, or even other conservation measures such as grass margins, end up with a predominance of the wrong type of weeds.

Rather than enhance biodiversity, this could smother beneficial arable plants.

The authors of the research say their results show that such conservation measures need very careful placement if they are to be successful and not over-run by less beneficial plants, such as grasses.

Dr Helen Metcalfe, who led the new study, said: “The location of these wildlife refuges is key in determining how successful they are in supporting important plant species, which provide food for farmland birds and habitats for pest-eating insects.

“By creating unsprayed strips of land away from sources of problematic weeds, we not only provide a refuge for the beneficial plants we want to protect, but we also reduce the risk of the wrong type of weeds invading the field and becoming a problem for crop production.”

Weeds can spring up in fields either from seeds that persist in the soil ‘seedbank’, or through ‘spill-over’ of seeds from adjacent areas, and its long been recognised that the diversity of weeds is much greater at the field edge than at its centre.

What wasn’t known was whether this was mainly because these margins typically receive less pesticides, or if it was due to colonization from nearby natural habitats.

The new study shows that it is predominantly the spill-over from the habitat on the other side of these ‘conservation headlands’ that is crucial in determining whether or not they will be a success.

The researchers analysed a dataset of almost 300 fields from across the UK’s main crop growing areas, to study the impact of the immediate landscape on the weeds in and around arable fields growing sugar beet, maize and oilseed rape.

They found 181 species of plants ranging from typical arable weeds such as field pansy, shepherd’s purse and fat hen, to perennial species typical of grasslands, like creeping bentgrass and red fescue.

Fields adjacent to grasslands had the greatest number of problematic weed species at their edges, whilst fields adjacent to bare ground had very low numbers of species.

Dr Metcalfe said: “Creating conservation headlands at the edges of fields near built up areas or water courses where there are few problem weeds nearby would reduce the spill over of these weeds from adjacent habitats and give the beneficial seeds already in the field the best chance to grow."