Print PageRecent experimental studies have provided evidence that greater species richness can increase the ability of plant communities to support multiple ecosystem functions. If biodiversity-ecosystem function research is to improve understanding of how and when ecosystem services depend on biodiversity, it will be necessary to achieve a broader scope of study than experimental systems. To assess whether plant diversity may improve the capacity of plant communities in agroecosystems to simultaneously sustain levels of multiple ecosystem services, an observational study was conducted in fallow fields of smallholder farms in western Kenya. Fallows in the study area provide multiple ecosystem services; here the focus was on wood production, livestock forage production, and soil formation. In 18 grazed fallows and 21 ‘improved’ fallows, stem diameter of trees and cover and height of shrub and herb species were measured, and were used to estimate biomass. Near infrared spectroscopy was used to predict soil properties (organic carbon, base cations, sand content), and steady infiltration rates were derived from asymptotic regression of ring infiltrometer data. For four ecosystem functions directed related to the focal ecosystem services (wood biomass, forage biomass, soil base cations, infiltration rates), we investigated whether plant species richness and functional diversity (FD) co-varied significantly with the proportion of functions above 50% of function maxima.
Results/Conclusions
In grazed fallows, the proportion of ecosystem functions above 50% of maxima increased with plant diversity, and declined at higher grazing intensity. At moderate grazing intensity, diversity effects appeared to be independent of grazing effects. In ‘improved’ fallows, the proportion of functions above 50% of maxima varied little, and was not explained by the plant diversity or abiotic conditions. Thus, apparent diversity effects on multiple ecosystem functions depended on fallow type. Differences between grazed and improved fallows may result from variation in disturbance, edaphic factors, and the diversity of fallow species and their functional traits. Diversity effects in grazed fallows may have occurred through complementary effects of species with different functional traits on different ecosystem functions, and through effects of some species on more than one ecosystem function. The observed patterns indicate that plant diversity may conditionally improve the ability of fallows to provide moderate levels of multiple ecosystem services to smallholder farmers, although effects are likely to vary with management and abiotic factors.
