Category: Valuation

More from a participant at the 6th Henry A. Wallace/CATIE Inter-American Scientific Conference on “Agrobiodiversity in Mesoamerica — From Genes to Landscapes” at CATIE in Costa Rica.

The ecologists at the Wallace Symposium today waded deeply into the functional role of diversity in agricultural systems. How much diversity do we need in order to get the full benefit of ecosystem services? Is some diversity redundant? What is the trade-off between a world of all things bright and beautiful and one of increased yields, healthy children and growing economies?

Prof. Teja Tscharntke of the Georg-August University in Göttingen presented numerous studies to illustrate the importance of at least a certain amount of wild biodiversity within or in close proximity to agricultural systems. In Andean potato systems, simpler landscapes, lacking heterogeneity in natural habitats, led to higher levels of the pestilential tuber moth and reduction in yields. Coffee systems in Indonesia near natural forest had higher bee species diversity and higher levels of seed set. Hand pollination of cacao had remarkably higher impacts on yields compared to the effects of other major variables, indicating the supreme importance of the near invisible midges that pollinate one of the most revered crops in the world.

But just how much of this wild biodiversity we need, and in what form, are just two of the many questions that are being posed. Teja brought up the SLOSS debate, dating back to the 1970s, of whether single, large or several small reserves will conserve more biodiversity. His findings suggest that many small habitats capture more heterogeneity. Fabrice DeClerck was back with a study of the relationship between species richness and function, using food crops as a model. In a study of households in Sauri in Kenya, he categorized food crops according to the nutrient services they provided — whether high in carbohydrates or proteins or specific vitamins, etc. Not surprisingly, functional richness (i.e. provision of all the major nutrients) was not necessarily associated with the highest species richness. You don’t have to grow everything to get your daily needs of protein and carbs, and for some nutrients (e.g. vitamin C) there is more species redundancy than others (e.g. folates). Well, I guess you had to be there!

The functional role of agrobiodiversity changes as you move from species to landscapes, and few principles can be transported across scales or systems. But that doesn’t stop a little healthy application of diversity when it’s needed. There was a nice case study of the use of plant diversity in and around Costa Rican farms of Dracaena to reduce pest populations that were causing exports of the ornamental plants to be held up by the US quarantine service. Secondary forest or certain types of cover crop can host populations of natural predators to the cicadellid pests. Consequently, the healthy plants passed through quarantine without a hitch and increased Costa Rica’s export revenues.