Jan 20, 2012
Does the cultivation of GM crops affect biodiversity?
Species diversity on farmland
Does the cultivation of GM plants affect biodiversity? This is a topic that has been discussed many times over the years. It is a fact that global biodiversity is shrinking and agriculture is one of the main causes. Monoculture and the use of pesticides and herbicides destroy large numbers of natural habitats, which reduces species diversity on agricultural land. Critics of plant biotechnology fear that this development will be exacerbated by the cultivation of GM crops. Numerous scientific studies have investigated how the cultivation of GM crops actually affects species diversity in fields.
One of the pests controlled with the help of genetically modified Bt maize is the European corn borer. Its larvae chew through maize stalks.
Ladybirds are also found on maize fields. They feed mainly on aphids and coccids and are therefore regarded as beneficial insects. Bt maize is not supposed to harm them or other non-target organisms.
Maize without weed control in the Üplingen display garden: certainly better for biodiversity on the field, but not for the growth of the crop plants or for field management.
Biodiversity or biological diversity refers to the variability of all living organisms. Biodiversity includes
- species diversity
- diversity within speci
- genetic diversity
- the diversity of ecosystems
The 1992 Convention on Biological Diversity set itself the target of protecting biodiversity and ensuring the sustainable use of its components. A supplementary agreement, the Cartagena Protocol, entered into force in 2003. It governs the handling of genetically modified organisms and contains measures to protect genetic resources and biological diversity against potential risks that may be associated with the release of GMOs.
Pest control using Bt plants: No danger to insects or soil-dwelling organisms
Ever since the first GM crops were planted that produce Bt protein to target specific pests, there have been fears that these proteins might also affect other insects and soil-dwelling organisms. All species that live on fields or in the soil and are not regarded as pests are referred to as non-target organisms.
A large number of separate studies have investigated the impact of Bt plants on various species and groups of non-target organisms, always in comparison with the cultivation of conventional varieties with and without the use of insecticides.
It has been demonstrated in principle that the cultivation of Bt plants does not have any negative consequences for non-target organisms. The use of insecticides had a much greater impact on species composition and abundance. In addition, field trials showed that the abundance and activity of the pests’ natural enemies were as high on fields with Bt plants as they were on fields with conventional plants. In 2007, an analysis of 42 field trials established that there was generally a greater abundance of insects and spiders in fields with Bt plants than in fields with conventional crops that had been treated with insecticides.
Other species, like predatory insects and insect-eating birds, can benefit from a greater abundance of insects and spiders because they feed on species that live on fields. A greater supply of food can promote biodiversity because food is available for a large number of species. A meta study conducted in 2008 found greater numbers of predatory species on fields with Bt plants than on fields with conventional plants that had been sprayed with insecticides.
Another 2008 study, which summarised the results of 70 scientific articles on soil organisms, showed that the cultivation of insect-resistant Bt plants had few or no effects on organisms in the soil, such as earthworms, nematodes and mites.
Weed control: Unavoidable reduction in species diversity
Weed control is a necessary farming activity that unavoidably hinders the promotion of species diversity. A high diversity of weeds on the field means competition for the crop plants and potential harvest losses.
The use of herbicide-resistant GM crops is a relatively new weed-control concept. The complementary herbicide to which the crop plant is resistant can be applied at any time during the growth phase without harming the crop.
In Britain, Farm Scale Evaluations were conducted from 2000 to 2003 to assess the impacts on biodiversity of cultivating herbicide-tolerant GM varieties. The evaluations covered 60 fields growing sugar beet, maize and oilseed rape. The results varied depending on the crop plant in question. Fields of GM sugar beet and GM oilseed rape were found to have fewer weeds and weed seeds than fields growing conventional sugar beet and oilseed rape varieties. This leads to a lower food supply for insects that feed on these plants. This in turn had an effect on the next predators in the food chain: fewer butterflies and bees were observed than on comparable conventional fields. By contrast, when it came to maize fields, conventional weed control was found to be more efficient: fields containing GM maize had more weeds and more insects than conventional maize fields.
A large-scale study with herbicide-resistant sugar beet in Denmark showed that species diversity on fields is significantly higher when herbicides are applied in doses that do not eliminate all weeds. The timing of the herbicide application is also important. In this study, researchers succeeded in selecting the herbicide dose and timing of the application in such a way as to produce a positive impact on the biodiversity of the agricultural ecosystems.
One positive effect on biodiversity of cultivating herbicide-tolerant GM crops is the associated reduction in soil tillage. When weeds are controlled in the conventional manner by ploughing, it entails a risk of soil erosion, reduces soil quality and threatens biodiversity. Various studies have shown that the cultivation of herbicide-tolerant GM plants brought with it a significant reduction in, and sometimes a complete absence of, tillage activities. This led to an improvement in the soil quality and to the protection of biodiversity both in the soil and above it.
Cultivation of high-yielding varieties can protect ecosystems
The biggest negative effect that agriculture has on biodiversity is caused by the loss of natural habitats when natural ecosystems are turned into agricultural land. The cultivation of new high-yielding varieties can reduce the pressure to find new land for agriculture because it enables more agricultural produce to be grown on existing fields to meet the rising demand. Above all, however, GM plants reduce harvest losses caused by pests, diseases and weed pressure, as was confirmed in a literature analysis conducted in 2010. Another 2010 study estimates that 2.64 million additional hectares would need to be found for cereal and oilseed rape worldwide if farmers were to stop growing GM crops. This means, they say, that the cultivation of GM plants helps ensure that fewer natural habitats are lost and that natural ecosystems are conserved.
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- Carpenter (2010) Impact of GM crops on biodiversity. GM crops 2:1, 7-23
- Marvier et al. (2007) A meta-analysis of effects of Bt cotton and maize on nontarget invertebrates. Science 316: 1475-1477
- Wolfenbarger et al. (2008) Bt crop effects on functional guilds of non-target arthropods: a meta-analysis. PLoS ONE 3:2118
- Icoz & Stotzky (2008) Fate and effects of insect-resistant Bt crops in soil ecosystems. Soil Biology and Biochemistry 40:559-586
- The Farm Scale Evaluations of spring–sown genetically modified crops (2003). Philosophical Transactions of the Royal Society B Vol.358(1439)
- Givens et al. (2009) Survey of tillage trends following the adoption of glyphosate-resistant crops. Weed technology 23: 150-155
- Sanvido et al. (2007) Ecological impacts of genetically modified crops: Ten years of field research and commercial cultivation. Adv Biochem Eng Biotechnol 107: 235-278
- Brookes et al. (2010) The production and price impact of of biotech corn, canola and soybean crops. AgBio Forum 13:25-52