The largest ever review of wildlife and organic farming has concluded that, on average, organic farms support 34 percent more plant, insect and animal species than conventional farms. Scientists from Oxford University examined data going back thirty years and found that this is a trend which has remained stable over time, and shows no signs of decreasing.

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For pollinators such as bees, the number of different species was 50 percent higher on organic farms.

Plant scientist Sean Tuck commented, "Our study has shown that organic farming, as an alternative to conventional farming, can yield significant long-term benefits for biodiversity. Organic methods could go some way towards halting the continued loss of diversity in industrialised nations."

Researchers examined the species richness of different farms – that is, the number of different species, rather than the individual plants and animals present. Tuck, the study's lead author added, "There are many ways to study biodiversity and species richness is easy to measure, providing a useful starting point. Broadly speaking, high species richness usually indicates a variety of species with different functions. Taking the example of bees, species richness would tell us how many different species of bee were on each farm but not the total number of bees."

The study, published this week in the Journal of Applied Ecology, looked at data from 94 previous studies covering 184 farm sites dating back to 1989. Researchers from Oxford University, working with colleagues from the Swedish University of Agricultural Science then re-analysed the data using satellite imagery to estimate the land use in the landscape surrounding each farm site to see if this had an impact on species richness.

They found that organic farms had a bigger impact on species richness when the land around them was more intensively farmed, particularly when it contained large tracts of arable land.

Dr Lindsay Turnbull, who led the research, commented, "We found that the impacts of organic farms on species richness were more pronounced when they were located in intensively-farmed regions. This makes sense because the biodiversity benefits of each organic farm will be diluted in clusters of organic farms compared to an organic 'island' providing rich habitats in a sea of pesticide-covered conventional fields.

"This effect was weakest in pollinators, which may be because pollinators are likely to visit neighbouring farms and could be affected by pesticides there."

However, the data suggested that the impact of organic farming varies (the average species gain was between 26 percent and 43 percent), which the researcher believe could be down to a number of factors including regional variation in farming practices and definitions of 'organic'. Dr Turnbull added, "Some conventional farms will intensively spray pesticides and fertilisers whereas others will use mixed methods of crop rotation and organic fertilisers with minimal chemical pesticides."

She continued, "The majority of the studies in our data were in developed nations with long histories of farming such as those in Western Europe. There, some wildlife have thrived in extensively managed farmland but are threatened by agricultural intensification.

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"However, in developing nations there is often great pressure on the land to provide enough food for local people, resulting in the conversion of natural habitat to farmland," Dr Turnbull said. "In such cases the benefits of organic farming are less clear, as this may require more land to achieve the same yield as conventional farming."

The researchers concluded that further study is needed to build a clearer picture of the situation in developing and sub-tropical countries and in soil biodiversity. Even so, they were confident enough in their findings so far to state that, "organic methods could undoubtedly play a major role in halting the continued loss of diversity from industrialised nations."

Organic farm groups in Europe have welcomed the investigation, which was supported by the Natural Environment Research Council (NERC) and published in the Journal of Applied Ecology on Monday. Louise Payton, policy officer at the Soil Association in the UK said, "This is fantastic news for wildlife and confirms what we have been saying for years. Our food systems are being threatened by the declines of bees and other pollinators - necessary for a third of the food that we eat. This research shows there is a clear solution for pollinators with a known outcome – support organic farming and we can have 50 percent more species of pollinators in our countryside."

Payton continued, "Yet in return for this, and many other benefits, UK organic farmers currently receive the lowest payments across the whole of the EU. We are urging the Government to redress this balance and ensure organic farmers in the UK are adequately supported in the new Common Agricultural Policy."