Seeds of conflict

Over the coming few weeks scientists will be poring over the results of one of the most important field experiments ever conducted in the UK. The findings will largely determine whether Britain will go ahead with the commercial growing of genetically modified (GM) crops. These "farm-scale trials" will be keenly scrutinised by a biotechnology industry keen to promote the introduction of genetically modified food to the UK, and by environmentalists who are equally keen to stop it - activists have mounted unsuccessful attempts to sabotage the trials.

Over the coming few weeks scientists will be poring over the results of one of the most important field experiments ever conducted in the UK. The findings will largely determine whether Britain will go ahead with the commercial growing of genetically modified (GM) crops. These "farm-scale trials" will be keenly scrutinised by a biotechnology industry keen to promote the introduction of genetically modified food to the UK, and by environmentalists who are equally keen to stop it - activists have mounted unsuccessful attempts to sabotage the trials.

Both sides of the debate agree that there has been a dire lack of research into the environmental impact of GM technology. This may be surprising given the thousands of square miles of farmland in America, China and elsewhere being planted with GM crops. But reading the first report of the government's GM Science Review, it quickly becomes apparent that there is very little hard experimental information about how exactly GM technology can affect wildlife and biodiversity. This, after all, is why the farm-scale trials were set up in the first place.

The trials are investigating the effects of just one type of genetic modification - the engineering of crops to be resistant to a broad-spectrum weedkiller. These herbicide-tolerant crops are grown extensively in America because they allow farmers to use a weedkiller that kills virtually every other plant in the field.

In the UK, three different crops are being studied - sugar beet, oilseed rape and maize - the trials involve planting between 60 and 75 fields with the GM and non-GM versions of each crop. An important feature of the experimental design is to grow GM and non-GM crops in the same field so that a direct comparison can be made when scientists look at the weeds, insects and other invertebrates that live in and alongside the cultivated area.

It is important to know what the trials do not address. The farm-scale evaluations (FSE) are not about the safety of GM food and human health. Nor do they address the issue of gene flow from GM to non-GM crops - a huge concern to organic farmers worried about GM pollen contaminating their plants. Neither do they directly measure the effect of GM crops on larger farmland animals, such as songbirds.

Essentially, the FSEs are testing a "null hypothesis": that there is no difference between GM and non-GM crops on the diversity of arable plants and invertebrates. If a difference exists, then the experiment is designed to identify and measure it - but only for these particular herbicide-resistant crops. Separate farm-scale trials will be needed for other GM crops in the future, such as pest-resistant plants engineered with a gene for a bacterial toxin.

The scientific consortium in charge of the FSE - led by Les Firbank of the Centre for Ecology and Hydrology in Cumbria - fears that some vested-interest groups may see too much into the outcome of the present trials. "Despite our efforts, we remain concerned that the findings will be over-interpreted, that they will be used as arguments for the widespread adoption, or rejection, of GM crops in general," the consortium wrote in a scientific paper published earlier this year in the Journal of Applied Ecology.

Dr Firbank says that these FSEs should be the start, not the end, of a much wider process of investigation into GM crops. "Our experiment deals with social and environmental issues that are relevant to Britain and, regardless of what we find here, that may not tell you anything valuable about what might be appropriate in other parts of the world," he insists.

Professor Chris Pollock of the Institute of Grassland and Environmental Research, who is helping to oversee the trials, is equally concerned about the public's misconceptions. "This is not about discussing agrochemicals poisoning birds," he says. "This is about share. What share of the agricultural resources is left [for wild animals and plants]?"

The GM Science Review has documented the overwhelming evidence showing that biological diversity within the British countryside has declined precipitously within the last 50 years or so. Ecologists blame this primarily on the loss of natural habitats accompanied by the increasing efficiency of British farmers.

"The decline of biological diversity within crops is not by and large caused by the toxicity of herbicides and pesticides, but by an increase in efficiency," Professor Pollock explains. "We can demonstrate that by seeing exactly the same phenomenon in grassland where herbicides and pesticides are not used. If you grow efficient grass varieties, you get fewer seed-bearing plants of other types and you impoverish the natural environment."

If Britain allowed the widespread commercial growing of herbicide-tolerant crops - which logic says would only be grown if farmers sprayed the appropriate broad-spectrum herbicide - there could, in theory, be a marked increase in the efficiency of farming. It stands to reason that this could continue the trend towards fewer wild animals and plants in the British countryside.

"We're trying to answer the question: 'will herbicide tolerance have an adverse effect on the environment because it increases the share that the farmer takes and decreases the share that's left?'" says Professor Pollock. He and the other scientists in the FSE consortium are concentrating on the weeds, beetles, bees, butterflies and snails that try to live alongside farm crops.

"This is all about how the lower part of the food web is going to divide and drive the diversity we desire so much," he explains. "This is a very European study because it is in Europe that farming and landscape go hand in hand."

Supporters of herbicide-resistant GM crops point to a couple of smaller studies that could indicate a positive environmental benefit of growing such genetically-engineered plants. One study, published earlier this year by scientists at the Broom's Barn research station in Suffolk, indicated that biodiversity could be increased within a GM sugar beet field if spraying was delayed until later in the season, allowing weeds to sprout, grow and set seed. In non-GM sugar beet, such a luxury is not allowed because conventional weedkillers have to be used as soon as weeds sprout.

However, as the GM Science Review points out in its assessment of this study, the experiment was small, complex and limited. It did not, for instance, look at the impact of herbicide spraying on subsequent weed populations within the field. The apparently beneficial results - the study showed that biodiversity was as high if not higher in GM sugarbeet fields - also depended on how farmers used the herbicide.

Again, this is why the larger, farm-scale trials are so important. They are designed to take farmers and their individual preferences and differences into account. "We went to real farms with real farmers. The difference between how they manage the crops is as important a part of the study as the effects of the herbicides themselves," says Dr Firbank.

Ultimately, he says, the null hypothesis will be tested and an answer found to one of the most pressing environmental issues of the day. "We have potential benefits and potential harm but no way of assessing the two without undertaking some formal studies," he says. "And that's what we're trying to do."