Tradeoffs and synergies of ecosystem services in diverse and non-diverse agroecosystems

Background/Question/Methods

Diverse agroecosystems are important providers of ecosystem services. Although many studies have investigated the individual ecosystem services provided by these systems, there is a need to quantify whether tradeoffs or synergies exist between individual ecosystem services. We considered several ecosystem services, including biocontrol and yield.  We hypothesized that more diverse agroecosystems would have a lower yield than less diverse agroecosystems, yet would also have higher rates of other ecosystem services. We conducted a meta-analysis to address the relationship between agricultural diversity and ecosystem services. We used research articles that reported the effects of increasing plant diversity, or landscape complexity in agroecosystems on yield and at least other ecosystem service (e.g. biocontrol, pollination). Each article reported both the yield and some quantitative measure of other ecosystem service (e.g pest damage on crops, pollination rates) in both diverse and non-diverse agroecosystems (e.g. monoculture vs. polyculture). Here we report the results obtained for biocontrol and yield.  We calculated effect sizes in terms of the logarithm natural of the ratios of yield and biocontrol measures in diverse and non-diverse agroecosystems and performed analyses to determine whether there was a synergy, tradeoff, or lose-lose relationship between yield and biocontrol.

Results/Conclusions

We found a slight, yet significant tradeoff between yield and biocontrol, with more diverse agroecosystems recording a lower yield but higher biocontrol effect (p- value=0.001). When separating the results by region-tropical vs temperate- the tropical studies did not show a difference in yield (p>.05), indicating benefits to biocontrol without a cost in yield in more diverse agroecosystems.   The overall result suggests that more diverse agroecosystems provide enhanced natural pest control services compared to non-diverse agroecosystems, but that these services may be accompanied by yield reductions. However, in the tropics it appears that more diverse agroecosystems do not present a tradeoff since pest control services are obtained without suffering yield reductions. We caution that an observed tradeoff does not signify benefits to intensive agriculture: when considering the overall benefits of diverse agricultural systems, farmers must consider a much broader scope than yield, including the overall financial costs of inputs and the potential gain from other ecosystem services, such as biocontrol, provided by diverse agroecosystems.