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Contact details:
GCTE Focus 4
Pablo Inchausti (Scientific Officer)
Laboratoire d'Ecologie
Ecole Normale Superieure
46 rue d'Ulm
Paris 75005
France
Tel: (+33) 1.44.32.23.16
Fax: (+33) 1.44.32.38.85
Research Highlights


Loss of biodiversity decreases biomass production in European grasslands

 Michel Loreau [loreau@ens.fr]
Leader of GCTE Focus 4 and Diversitas Core Program Element 1

 


The debate about the relationship between biodiversity and ecosystem functioning has been intensively investigated over the last few years. The main hypothesis is that loss of species diversity will be detrimental to key ecosystem processes such as primary productivity. The implication is that the continuous loss of biodiversity due to human intervention will cause loss of ecosystem services fundamental for the human enterprise and well-being. The hypothesis is highly controversial and has been proved by some studies and rejected by others.

 

To test this hypothesis a major effort has taken place in Europe under the umbrella of BIODEPTH (BIODiversity and Ecosystem Processes in Terrestrial Herbaceous ecosystems: experimental manipulations of plant communities), a project funded by the European Union with eight experimental sites in seven countries (Germany, Greece, Ireland, Portugal, Sweden, Switzerland and United Kingdom) and a modelling component in France. The team of scientists used standardized protocols in all experiments to assemble grassland communities with different plant richness levels ranging from monocultures to high diversities that match natural background levels.


Figure 1. Productivity declines with the loss of plant diversity. (A) Overall log-linear reduction of aboveground biomass with the simulated loss of plant species richness. (B) Linear reduction with the loss of functional group richness at different species richness levels. Copyright Science.

After two years of the newly established communities, the results show an overall reduction of aboveground biomass production with loss of species, supporting the above hypothesis (Figure 1A). The relationship was best described by a linear relation between productivity and the logarithm of the number of plant species. In addition, for a given species richness, communities with fewer functional groups were less productive (Figure 1B). The functional groups were categorized in three types: graminoids (grasses), nitrogen-fixing legumes, and other herbaceous species (herbs).


Figure 2. Biomass patterns at each site (displayed with species richness on a log2 scale for comparison with Fig. 1A). Best-fit models from individual sites based on adjusted R2 are as follows: log-linear in Switzerland and Portugal; linear (untransformed species richness) in Germany and Sweden; quadratic in Sheffield; ANOVA with five species richness levels (significant treatment effects with no simple trend) in Ireland and Silwood; and no significant effect in Greece. Copyright Science.

The results also highlight the importance of considering scaling issues when analyzing the relationship between biodiversity and ecosystem functioning. When all sites were analyzed together, the best fit was a log-linear regression with parallel slopes (Figure 1A), and the interaction between location and species richness was not significant. However, when the analyses were done for each site independently, the best fit was achieved by a variety of different models (Figure 2). This apparent contradiction shows the higher statistical power of multi-site experiments as opposed to individual-site experiments with lower replication, stronger contingency and, therefore, lower statistical power to detect overall treatment differences across sites. The experiment also reveals the relative effects of other variables on overall biomass production: plant species richness, location, and species composition explained approximately 18, 28, and 39% of variations in aboveground productivity.

For further information on BIODEPTH results, please refer to Hector et al. (1999) Plant diversity and productivity experiments in European grasslands. Science 286: 1123-1126.