Estimating the independent effects of different components of organic farming on biodiversity

Agriculture is currently the largest threat to biodiversity of birds globally and is likely to be a major threat to other taxa. Thus understanding how to integrate farming and wildlife together successfully is a major goal for conservation ecologists. Organic farming is one method that increases biodiversity relative to conventional methods of agriculture. Developed countries have seen huge growth in organic farming over the last 20 years owing, to a large extent, to consumers' perceptions of the perceived environmental benefits of organic farming. By promoting biodiversity and reducing chemical inputs, organic farming could deliver important ecosystem services, including higher pollinator abundance and cleaner waterways. Many studies have compared biodiversity on organic and conventional farms or focussed on individual components of organic farms (e.g. on the effects of spraying or non-cropped habitats on biodiversity). Both recent reviews of the two agricultural methods concluded that there is more biodiversity on organic than conventional farms; however, neither could identify which features of organic farming are of particular benefit to biodiversity. We propose a meta-analysis to disaggregate the effects of different components of organic farming, thereby identifying which of those components are responsible for the observed increases in biodiversity (plants, invertebrates, birds, mammals) on organic farms relative to conventional farms. This is the next logical step in understanding the relationship between increased biodiversity levels and organic farming practices. Further reviews of biodiversity on organic and conventional farms may be carried out, but it is unlikely that they will reveal which components of biodiversity are driving the observed relationship. Similarly, more empirical, hypothesis-driven studies of individual components could also be conducted. However, they would necessarily be expensive, time consuming and potentially, assuming the data already exist to infer which organic practices contribute most to biodiversity, unnecessary. Only once our meta-analysis is complete does it seem sensible then to carry out hypothesis driven research on individual organic management components or combinations of components. Thus the results of our review will be an important step forward in our understanding of what drives increased biodiversity on organic farms, and will have implications for policy and for the direction of future scientific work on organic farming. Previous studies have reported that organic farms have taller and wider hedgerows, more grass margins, a greater area of woodland and more heterogeneous cropping than conventional farms. All of these features have been positively related to abundance/diversity of some or all of the wildlife groups that we intend to study; however, they do not form part of the incentive schemes for organic farming. Thus, there is the potential that the biodiversity benefits of organic farming are decoupled from the payments made to farmers under organic farmer schemes (currently twice those made to farmers for environmentally sensitive stewardship of conventional farms). In this project, we aim to analyse existing data to examine how the different component parts of organic farming contribute to the observed increase in biodiversity on organic farms (relative to conventional farms) by estimating effect sizes for each component part. In this way, we aim to identify whether more targeted schemes can yield the same biodiversity benefits as organic farming, without a wholesale change in management. Modern agriculture faces a conflict between demand for increased production and awareness of the environmental need for reduced intensity. If policy makers are to resolve this conflict, it is essential that scientists are able to provide estimates of the costs and benefits of individual agricultural policies. The work that we propose is a necessary step towards that goal.