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Environnement

The benefits of biodiversity

 
 
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Experimental site at Silwood Park (UK) - Demonstrating the fundamental role of diversity.

Some fifty European researchers have observed, measured and compared the effects of biodiversity and the consequences of its loss. This large-scale project covered all climates and all latitudes of the continent. Their conclusions contradict the growing trend to promoting single-crop farming. Their meticulous work shows that the most uniform areas are also the poorest and that there are many facets to the richness of biodiversity.

  "Despite the results of the forced techniques of modern farming, our instincts continued to tell us that biodiversity had an impact on the total resources of ecosystems and that this simplifying

agricultural model did not apply in reality. But this had never been confirmed. We wanted to demonstrate that, in a rich community of species, different varieties spontaneously occupy a particular niche and use resources differently, with the result that a mixed field produces more than a monoculture," explains John Lawton of the NERC Centre for Population Biology (CPB) at the Imperial College of Science, Technology and Medicine, coordinator of the Biodepth project and Chief Executive of the UK's National Environmental Research Council (NERC).

A continental experiment

This vast project brought together about 50 researchers from 11 universities in 8 European countries. The teams observed, measured and analysed the effects of biodiversity - and its absence - over a three-year period (1996-1998). Their field of observation consisted of 480 sites each covering 4 m2, located along two major axes running diagonally across the continent from the north-west to the south-east (Ireland, United Kingdom, Germany, Switzerland, Greece) and from the north-east to the south-west (Sweden, Portugal) in order to be able to take into account the continent's different environments, climates and latitudes. This scientific experiment - the most extensive of its kind anywhere in the world - was particularly interesting as it was conducted across an entire continent.

  • The field sites were first sterilised to eradicate all plant life so as to guarantee the purity of the experiments. Each site was then planted in a specific way ranging from a single species to a varied mix. Native species were used and their combination was determined with reference to strict criteria of biodiversity, taking account not only of the number of species but also of the functional groups to which they belong - legumes, grasses or herbs.

The entire process was studied, from germination to decomposition. Productivity was measured, the vegetation was weighed on maturity, soil samples were taken, insects listed (like other animals, insects have a mutually dependent relationship with the plants), plant decomposition and soil composition analysed, and soil humidity and water retention measured.

Productivity, complementarity, interaction

"We showed that a more diverse community has better productivity without adding fertiliser. No doubt the plants are better able to absorb the nitrogen. There is therefore less nitrate in the water, which has a beneficial effect on human health", comments John Lawton. However, the benefits of biodiversity are more than quantitative. When biodiversity breaks down or is lost, the ecosystem as a whole is disrupted. Plant resistance and health is reduced. Insects decrease in number and variety. Invertebrate populations change, resulting in potentially negative impacts on soil chemistry and the recycling of mineral elements. Researchers recorded these effects at all the field sites, despite differences in climate, soil type and plant species.

  • The Biodepth project also indicated the importance of complementary riches within a rich plant community. Different species occupy a particularly niche and use different resources. Some plants draw on nutrients near the surface, whereas others take their sustenance from deeper down in the soil. When grouped together, these different species can therefore use more nutrients in total - such as nitrogen and phosphorous - than if they were planted as a monoculture. This is why biodiversity is so important to the food chain and why the concept has major implications for agriculture.

In addition to the notion of complementarity, there are a number of other hypotheses relating to the beneficial effects of mixed plant communities. One notion is that of positive interactions by which one species effectively "encourages" a different species and is thus in itself a factor for biodiversity. In extreme situations, such as drought, one plant can create shade that helps a new plant to become established. There could also be other types of very specific mutually beneficial interaction.

"We want to conduct experiments of the same type, this time studying the impact of biodiversity in an environment which changes over time", comments Michel Loreau, Profession of Ecology at the Université Pierre et Marie Curie (Paris VI), and responsible for developing the mathematical theories and models used in the Biodepth project. "By subjecting this environment to different phenomena - drought, frost, fire, or added nitrogen - we will try to show the importance of biodiversity under these conditions and also its potential significance in the event of climate or environmental change, for example."

By artificially creating heat or cold, European researchers will therefore be able to improve their knowledge of complementarities and interactions between species in order to better identify the true implications of biodiversity - a biodiversity shown by their research as playing a fundamental role in ecosystems.

   
 
Title
Bio-Diversity and Ecological Processes in Terrestrial Herbaceous Ecosystems: experimental manipulations of plant communities (BIODEPTH)

Programme
Environment and climate
(ENV 2C)

Reference
ENV4-950008

Contact
Phil Heads
Centre for Population Biology - Imperial College at Silwood Park, Ascot (UK)
Fax : +44-1344-873173
E-mail: p.heads@ic.ac.uk
http://forest.bio.ic.ac.uk/cpb/
cpb/biodepth/contents.html

Partners
- Imperial College of Science, Technology and Medicine, Ascot, United Kingdom (coordinator)
- Instituto Superior de Agronomia, Lisbon, Portugal
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield, United Kingdom
- Laboratoire d'Ecologie, Université Pierre et Marie Curie, Paris, France
- Institut für Umweltwissenschaften, Universität Zürich, Zurich, Switzerland
- National University of Ireland, Cork, Ireland
- Department of Environmental Studies, University of the Aegean, Lesbos, Greece
- The Swedish University of Agricultural Sciences, Umea, Sweden
- Lehrstuhl für Pflanzenökologie, Universität Bayreuth, Bayreuth, Germany

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The crop, before weighing.
Measuring productivity.

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