The loss of biodiversity in European grasslands will make them less productive, reducing the amount of energy available to the rest of the food chain and threatening the overall health of the ecosystem, say results from one of the world's most extensive ecological studies (Science 5 November 1999).
BIODEPTH (Biodiversity and Ecological Processes in Terrestrial Herbaceous Ecosystems) is an EU-funded programme as part of the Terrestrial Ecosystem Research Initiative (TERI). A team of 34 scientists from 8 European countries participated in this study, establishing a network of European field sites in natural and semi-natural plant communities along a North-West to South-East (Ireland to Greece) and a North-East to South-West (Sweden to Portugal) gradient through Europe. The German measuring site near Bayreuth was co-ordinated by Prof. Dr. E.-D. Schulze, Max Planck Institute for Biogeochemistry, Jena, and his team from the Max Planck Institute and the University of Bayreuth.
Within BIODEPTH - a multinational collaboration to perform the same standardised experiment at a continental scale - experimental grassland communities were established that mimicked the gradual loss of biodiversity seen throughout Europe by creating replicate plant communities with reduced species richness. On each site, effects of reduced biodiversity on key ecosystem processes and structural characteristics were determined and quantified. The German site at Bayreuth focused on effects on productivity, nutrient cycling, soil nitrate leaching, decomposition, canopy architecture, competition and population biology of species involved.
The experimental manipulation of plant species diversity significantly changed the dynamics of those ecosystem processes. It affects ecosystem functioning and population dynamics. The productivity decreased linearly with decreasing species richness – plant communities grow better in species-rich teams. Harvest yields were found to increase when there was a range of plants with different characteristics growing together. Similar patterns occurred in a broad range of European grasslands, making the findings applicable on a continental scale. Concentrations of soil water nitrate were higher than the European official limit for drinking water under situations of low diversity. Functional characteristics of plant species - especially the ability to fix nitrogen - play a major role for several ecosystem processes and are at least as important as their number per se. Ressource-use complementarity in more diverse systems could explain the higher productivity and lower nitrogen losses.
These findings represent the latest development in the scientific debate about how the loss of biodiversity affects the way in which ecosystems function - recently a major focus of ecological research. The BIODEPTH evidence provides a vital contribution to the debate by demonstrating that both numbers of species and the types of plant play important roles in ecosystems.
The authors claim that their experimental evidence should send a clear message to European policy makers: that preserving and restoring biodiversity is beneficial to maintaining grassland productivity - particularly if reductions in fertiliser and pesticide usage are to be achieved. About half of Europe’s farmland is grassland (60 million hectares), used as grazing pastures, hay meadows, and as set-aside land. The loss of species is playing a key role in the gradual erosion of the quality of our environment. "In addition to moral and aesthetic reasons to conserve biodiversity, our results now provide strong scientific reasons, too," says Dr Andy Hector of Imperial College, lead author of the group’s report in Science. "These results provide the type of general ecological principles needed for European conservation and agricultural policies". This project signals the beginning of a new era by demonstrating the power of "big ecology" to underpin environmental policymaking.
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