Enhancing agroecosystem performance and resilience through increased diversification of landscapes and cropping systems

Over the past two decades, ecologists have gained a considerable amount of insight concerning the effects of biological diversity on how ecosystems function. Greater productivity, greater carbon sequestration, greater retention of nutrients, and greater ability to resist and recover from various forms of stress, including herbivorous pests, diseases, droughts, and floods, are among the effects of increased biological diversity noted in a recent review by Cardinale et al. (2012). The latter effect, often called resilience, is particularly important in managed social-ecological systems, including agroecosystems (Walker and Salt, 2006). In addition to being better able to withstand and recover from disturbances due to pests, weather, and other biophysical factors, resilient agroecosystems can be less susceptible to fluctuations in production costs and market prices (National Research Council, 2010; Kremen and Miles, 2012). In general, the relationship between biological diversity and ecosystem function resembles an asymptotic hyperbola (Cardinale et al., 2012). That is, increases in the number of species present in an ecosystem from a very low level to some intermediate level engender large changes in ecosystem function, whereas increases in species richness above some intermediate, and undetermined, value engender smaller effects. Another way to look at biodiversity-ecosystem function relationships is through the lens of losing species diversity. Professor Shahid Naeem of Columbia University uses the following analogy to examine how many species might be lost from an ecosystem before critical functions are no longer available: Imagine you have a computer on your desk that works well. Now open it, reach in with a needle nose pliers and randomly remove five of the many parts of the motherboard. Do you expect the computer to continue to function well after the loss of those parts? The development of modern, industrial agriculture has been characterized by large reductions in biological diversity, both across landscapes and within farming systems (DeFries et al., 2004; Vandermeer et al., 2005). This loss of biodiversity is particularly evident in the U.S. Corn Belt. Where species-rich prairie grasslands, wetlands, and oak savannas once grew, corn and soybean now dominate (Klopatek et al., 1979). Farming systems that once contained small grains, hay, and pasture in addition to corn and soybean now contain almost exclusively the latter two crops (Hatfield et al., 2009; Brown and Schulte, 2011; Johnston, 2013). In Iowa, which has lost proportionally more area of its native vegetation than any other U.S. state (Klopatek et al., 1979), corn and soybean now occupy 63% of the state’s total land area and 82% of its cropland (National Agricultural Statistics Service, 2014). Simplification of crop and non-crop vegetation in the Corn Belt has been a strategy pursued through decisions and actions of individual farmers and through federal and state policies, with a goal of producing huge amounts of corn, soybean, chickens, cattle, hogs, ethanol, and farm revenue (Durrenberger and Thu, 1996; Secchi et al., 2009; Nassauer, 2010; McGranahan et al., 2013). It has also been concomitant with simplification of management strategies and increases in scale ( Johnston, 2013; McGranahan, 2014). Nonetheless, despite impressive gains in farm productivity and revenue, Corn Belt agricultural systems and the region’s residents are threatened by a number of emerging and continuing challenges, including soil erosion, water quality degradation by nutrient and pesticide emissions, greater prevalence of herbicide-resistant weeds, volatility in production costs and crop prices, loss of knowledge and infrastructure to support diverse markets, and declines in rural community vitality (Tegtmeier and Duffy, 2004; Alexander et al., 2008; Sullivan et al., 2009; Brown and Schulte, 2011; Sprague et al., 2011; Mortensen et al., 2012; Heathcote et al., 2013). Perhaps most Domain Editor-in-Chief Anne R. Kapuscinski, Dartmouth