Scaling-up agroecological research to investigate tradeoffs in ecosystem services

Background/Question/Methods

Biologically-based diversified farming systems, defined as systems that maintain plant and animal functional diversity across spatial and temporal scales, may promote the regeneration of ecosystem services such as soil fertility, pest control, and water quality.  They may thereby enhance sustainability and reduce negative externalities often associated with chemically-intensive monocultures, such as pesticide poisoning and eutrophication. However, the regeneration of ecosystem services that provide essential inputs to agriculture may come at the expense of short-term crop yields.  We evaluated the fundamental tradeoff between provisioning (i.e. food production) and regulating ecosystem services under different types of farm management by scaling-up from on-farm studies, which are typically limited both in spatial and temporal extent, and in the number of ecosystem services they target. We used both classic meta-analysis (analysis of effect sizes from multiple studies) and quantitative synthesis (analysis of original data from multiple studies) to draw generalizable conclusions on how biologically diversified versus simplified, chemically-intensive farming affect different ecosystem services and their tradeoffs.  

Results/Conclusions

For example, for pollination services, we found that local-scale diversification, organic management and high-quality habitats surrounding farms, each additively increased pollinator (bee) community abundance and richness, supporting the concept that multi-scale diversification is needed to promote some ecosystem services.  Further, synthesizing across published meta-analyses and quantitative syntheses, we found evidence that biologically-based and/or diversified farming systems supported significantly greater regulating ecosystem services than chemically-intensive agriculture, although not always at the economic levels required by growers.  Enhanced regulating services may trade off with provisioning services; a recent meta-analysis concluded that organic crop yields were lower than conventional by 25% (+4% CI).  However, we re-analyzed the data to better account for its hierarchical structure, finding that the results were quite sensitive to specific studies, which suggests greater uncertainty regarding the assessment of the yield gap than previously estimated. Further, we found that some organic management practices reduced the yield gap.  These results suggest that further agroecological research is needed, both to assess the magnitude of the yield gap, and to identify agronomic techniques that contribute substantially to food production without trading off ecosystem services and thus the essential resilience and sustainability of the agricultural enterprise.