Agri-environmental schemes have changed Britain’s landscape – but there is a mixed picture of environmental winners and losers, said a survey which is directing DEFRA policy.

The Countryside Survey 2007, commissioned by DEFRA and the Natural Environment Research Council (NERC), cost £10m. It revealed that farmland has become much less trimmed and less-intensively managed in the past 30 years – especially in the last nine years.

This has caused nettles, hawthorn and brambles to flourish in farm margins.

But while these big weeds have provided a habitat for dormice, hedgehogs and caterpillars, they are killing off small plants like harebell and wild strawberry.

Broad-leaved woodland areas have increased by 7% in 1998-2007 – but the overall length of hedgerows has fallen by 6%.

Lead author Peter Carey, from the Centre of Ecology and Hydrology, said that schemes such as ELS and HLS had mostly been effective.

“If one species flourishes, another must suffer,” he said. “But creating small wildlife habitats in farm margins is vital for the environment and needs more funding.”

He noted concern about the uplands landscape, however. The national sheep flock has halved since 1988, leaving many areas of moor overgrowing into tall weeds.

“63% of eligible farmland is covered by an agri-environment scheme – which shows that farmers are making a big commitment to the countryside environment,” said Diane Mitchell, the NFU’s chief environment adviser.

The survey is the biggest of its kind. There have been five such DEFRA surveys since 1978, which Ms Mitchell says are an “invaluable tool” to monitor climate change.

Ms Mitchell also said that the data could give farmers guidance on how to meet the production demands of a growing population sustainably.

Paul Temple, the NFU’s vice-president, praised farmers for their environmental management – saying that many farmers do extra environmental work voluntarily.

“The mixed picture …demonstrates the complexity and number of differing factors affecting our countryside,” he said.