Abstract
We hypothesize that biological diversification across ecological, spatial, and temporal scales maintains and regenerates the ecosystem services that provide critical inputs-such as maintenance of soil quality, nitrogen fixation, pollination, and pest control-to agriculture. Agrobiodiversity is sustained by diversified farming practices and it also supplies multiple ecosystem services to agriculture, thus reducing environmental externalities and the need for off-farm inputs. We reviewed the literature that compares biologically diversified farming systems with conventional farming systems, and we examined 12 ecosystem services: biodiversity; soil quality; nutrient management; water-holding capacity; control of weeds, diseases, and pests; pollination services; carbon sequestration; energy efficiency and reduction of warming potential; resistance and resilience to climate change; and crop productivity. We found that compared with conventional farming systems, diversified farming systems support substantially greater biodiversity, soil quality, carbon sequestration, and water-holding capacity in surface soils, energy-use efficiency, and resistance and resilience to climate change. Relative to conventional monocultures, diversified farming systems also enhance control of weeds, diseases, and arthropod pests and they increase pollination services; however, available evidence suggests that these practices may often be insufficient to control pests and diseases or provide sufficient pollination. Significantly less public funding has been applied to agroecological research and the improvement of diversified farming systems than to conventional systems. Despite this lack of support, diversified farming systems have only somewhat reduced mean crop productivity relative to conventional farming systems, but they produce far fewer environmental and social harms. We recommend that more research and crop breeding be conducted to improve diversified farming systems and reduce yield gaps when they occur. Because single diversified farming system practices, such as crop rotation, influence multiple ecosystem services, such research should be holistic and integrated across many components of the farming system. Detailed agroecological research especially is needed to develop crop- and region-specific approaches to control of weeds, diseases, and pests. © 2012 by the author(s).
Highlights
While modern, industrialized agricultural systems in theory produce sufficient food to feed the world’s current population, they have accomplished this feat with significant ecological and social externalities (Hazell and Wood 2008)
We found that compared with conventional farming systems, diversified farming systems support substantially greater biodiversity, soil quality, carbon sequestration, and water-holding capacity in surface soils, energy-use efficiency, and resistance and resilience to climate change
Seufert et al attributed their finding of a larger yield gap in developing countries to the atypically high conventional yields found in those studies, relative to local averages
Summary
While modern, industrialized agricultural systems in theory produce sufficient food to feed the world’s current population, they have accomplished this feat with significant ecological and social externalities (Hazell and Wood 2008). We define a diversified farming system as a system of agricultural production that, through a range of practices, incorporates agrobiodiversity across multiple spatial and/or temporal scales (Altieri 2004, Pearson 2007, Jackson et al 2009, Tomich et al 2011, Kremen et al 2012). Across spatial scales, diversified farming systems promote agrobiodiversity through practices located within field (e.g., composting, intercropping, insectary strips, agroforestry), across the whole field (e.g., crop rotations, cover cropping, fallowing), around field perimeters (e.g., hedgerows, border plantings, grass strips), across multiple fields (mosaics of crop types and land-use practices), and at Ecology and Society 17(4): 40 http://www.ecologyandsociety.org/vol17/iss4/art40/
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