Letter: Case for GM trials

Sir: I have been away from the UK and have only just received a copy of Natasha Walter's article "In the fields of conflict" (2 August). Ms Walter criticises the government-funded experiments that will study the environmental consequences of field-scale cultivation of herbicide- tolerant GM crops. She accuse them of being unscientific because they do not include baseline measurements of diversity and because the sites are open to long-range movements of organisms between the GM and control fields.

I chair the scientific steering committee that will oversee these studies. They will be carried out at a number of different paired sites, in order to make the comparisons statistically valid. The fact that we are studying differences between paired sites (GM and non-GM) makes it unnecessary to have baseline measurements of diversity, and replicate sites will, of course, be exposed to the same influences from broad-foraging organisms. Although the aim of this study is specifically to examine the influence of GM on biodiversity within current intensive farming systems, the data will be compatible with those accruing from parallel studies on diversity in other systems.

My committee, selected on the grounds of the expert knowledge of its members across the range of ecological, statistical and environmental issues relevant to the study, is independent of both the sponsoring departments and the contractors. We deplore the attempts to prevent the study from going ahead by damaging experimental sites.

The essence of the studies, which encompass three cropping systems (spring- and winter-sown oilseed rape and forage maize) is to measure the abundance of a range of indicator species within field-scale plots. This will permit us to compare the values between GM crops grown according to the seed producer's recommendations and non-GM varieties grown according to current farming practice. The publication of the results will be a useful contribution to the debate about the role of GM crops in UK agriculture.

Professor CHRIS POLLOCK

Chair, GM Crop Farm-Scale Evaluation Steering Committee

Aberystwyth, Ceredigion