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Agricultural Systems: balancing ecological, economic, energetic, and social tradeoffs
Ecosystem definitions encompass spatial entities, the interactions between biotic and abiotic elements in a given region, as well as the functional connections between organisms and the physical environment and among resident organisms (Ehrenfeld et al., 1997). Agricultural systems are ecosystems that are managed to provide goods and services, primarily for human consumption. Most agricultural expansion requires conversion of land from native ecosystems (i.e. forests or savannahs) in order to grow crops and raise livestock. Land-use change to intensively managed agroecosystems involves tradeoffs: increasing food production capacity to meet human demand may come at the expense of shifts (or losses) in the functional connections of native ecosystems. Ecologists have described these tradeoffs in terms of phases of ecosystem development and quantified them as the relationship between primary production and biomass. Assessment of social, economic, energetic, and ecological tradeoffs provides an effective framework for evaluating agroecosystems. Contrasting agricultural extensification at the global scale and with the regional management focus of agroecosystems in California’s Sacramento Valley demonstrates distinct management approaches and their global- and regional-scale impacts.
- 1 Ecosystem development theory
- 2 Global-scale agriculture and land-use change
- 3 Change in ecosystem function and positive feedbacks
- 4 Population growth, increased production demand
- 5 Economic drivers of agricultural expansion; commodity exports
- 6 Energetically inefficient agroecosystems
- 7 Regional case study: California’s Sacramento Valley
- 8 Literature Cited
Ecosystem development theory
Eugene Odum (1969) described a fundamental conflict between production strategies seen in native ecosystems and intensively managed agroecosystems in The Strategy of Ecosystem Development. Agriculture and intensive forestry strive for high productivity of harvestable crops, with little of the landscape’s biomass left unharvested. This can be illustrated as a high productivity to biomass ratio (Figure 1, lower graph). Native ecosystems exhibit the reverse strategy: a high biomass to production ratio (Figure 1, upper graph). Phases of ecosystem development, or succession, demonstrate the same concept (Odum, 1969). Developing and maintaining an ecosystem’s early successional phases, frequently in a monoculture, has been the industrialized approach to achieving large harvests (Odum, 1969); post Green Revolution agricultural management typifies this method. Native ecosystems, when left unmanaged and undisturbed, tend towards greater diversity and biomass, which can be seen in transitions between early successional phases, such as grasslands, to later phases with denser, woody plants (however, progression among phases need not always be linear and unidirectional (Egerton, 1973)).
Odum observed that the additional services rendered by ecosystems (beyond food and fiber) such as water filtration, gas exchange, and nutrient cycling are often best provided by less productive landscapes. In these areas harvestable productivity remains low, but biomass and diversity are high (note in Figure one R, community respiration, is higher in the native forest ecosystem (upper graph) than the intensively managed microcosm (lower graph). Historically ecosystem services have been undervalued in comparison with production capacity, perhaps due to their spatial and temporal separation from harvested goods (Chapin, 2006).
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Figure 1: Comparison of the time scales and bio-energetics in a forest system (top) and laboratory microcosm (bottom) succession. PG is gross production; PN is net production; R is total community respiration; and B is total biomass (adapted from Odum, 1969).
However, more emphasis is currently being placed on weighing immediate costs and benefits against long-term impacts and hidden expenses. Measurements are being used to assign economic values to the ecosystem services necessary for sustained production at global, national, and regional scales. Odum’s ecosystem development framework called for objective evaluations of intensive ecosystem management, with a focus on answering the question of how much production is necessary and assessing the costs incurred at high production levels. Integrated consideration of the social, economic, energetic, and ecological tradeoffs that drive agricultural production levels provides an effective framework for this evaluation.
Global-scale agriculture and land-use change
DeFries et al. (2004) calculated that 83 percent of the earth’s land surface is affected by human influences, both direct and indirect. Agricultural production accounts for approximately one third of this use; 12 percent is dedicated to cropland and pastureland covers the remaining 21 percent (DeFries et al., 2004). Agricultural extensification is a major driver of land-use changes, which are often accompanied by ecological costs such as loss of biodiversity, reduced watershed health, and climate change feedbacks (DeFries et al., 2004). Matthews et al. (2000) estimated the conversion of native ecosystems for agricultural use has reduced previously forested lands by 20 to 50 percent over the past three centuries.
Change in ecosystem function and positive feedbacks
Agricultural production increases the share of primary production allotted for human consumption while decreasing the share available for other ecosystem functions (DeFries et al., 2004). This ecological tradeoff associated with land-use change is further complicated by positive feedbacks, processes that describe how small changes build one upon the next in a self-reinforcing cycle. Positive feedbacks are typically destabilizing and can make it difficult to maintain ecosystem services and functions, and it is nearly impossible to recover them once lost. The Amazon basin is exemplary of this type of effect.
Much of Amazon wild land is rainforest that is being transformed through clear-cutting to make way for grazing area and field plantings. The loss of dense vegetation is linked with reduced precipitation, cloudiness and rainwater cycling. Once these climatic factors have changed, regeneration of the original vegetation is often impossible (Werth et al., 2001). Without dense vegetation, precipitation and rainwater cycling is further reduced, and the problem intensifies (Figure 2). The Amazon is an example of one of many zones where agriculture is rapidly expanding and ecosystems are intensively managed for production; regional availability of land, water, and favorable climatic conditions are common among areas of high exploitation. Increased yields available through clear cutting come at the expense of eliminating diverse, high-biomass systems and successional stages as well as the ecological services they support.
Insert Figure Two here
Figure 2: Amazon forest mosaic. Clockwise from top left: forested area; clear-cut area for soy planting; clearcut area with several unremovable trees. The loss of dense vegetation for crop planting has been linked with reduced rainwater cycling, precipitation, and cloudiness. Changes in these factors over a large area may make regeneration of the original vegetation impossible.
Population growth, increased production demand
Environmental costs are intrinsically interrelated with human social and demographic considerations; agricultural extensification is among the leading causes of native ecosystem conversion and habitat loss. The global population is projected to increase 50 percent by 2050; this population growth, as well as demand by wealthy nations for diets rich in meat, is expected to contribute to a doubling of global food demand in the next half-century (Tilman et al., 2001).
If present extensification rates continue, pastureland is anticipated to increase by 5.4 x 108 hectares prior to 2050 and cropland would expand by 3.5 x 108 hectares, making the combined total agricultural land base 18 percent larger than today, an area roughly the size of the continental United States. Due to regional land availability, much of the land-use change is expected to take place in Latin America and Sub-Saharan central Africa (Tilman et al., 2001).
The Green Revolution has been credited with doubling grain production within the first 35 years of its inception. Although this dramatic production increase reduced food shortages (an achievement from a socio-political perspective), it did not address distribution dilemmas and came at high ecological cost. Previously self-sustaining ecological services, such as soil fertility, had to be supplemented with chemical and energetic inputs due to overexploitation (Pollan, 2006). Loss of biodiversity exemplifies the negative ecological consequences of managing a large portion of the land surface in monoculture and preventing it from moving beyond early successional stages (Odum, 1969). Biodiversity loss has been correlated with loss of ecosystem services such as carbon storage, flood control, forage production, and water provision, (Chan et al., 2006).
Economic drivers of agricultural expansion; commodity exports
Economic incentives of expanding production capacity are major drivers of extensification, particularly in agricultural export commodities. Viticulture expansion in South Africa’s Cape Floristic Region typifies economic and ecological tradeoffs. Wine grape production is the fastest-growing and most economically lucrative agricultural business in the Western Cape since trade sanctions were lifted in 1992 (Cape Wine Academy, 2002; Fairbanks et al., 2004). The Cape Floristic Region is the smallest of the six floral kingdoms found throughout the world; the 90,000 km2 region in southwestern South Africa is considered a global conservation priority due to its “extreme endemic floristic biodiversity among the world’s Mediterranean ecoregions” (Myers et al., 2000; Fairbanks et al., 2004).
Predictive land use modeling has indicated that more than 14,849 hectares of the most threatened habitats are considered particularly suitable for vineyards (Fairbanks et al., 2004). However, the native vegetation that is most frequently converted, breede fynbos/renosterveld, is considered irreplaceable to conservation priorities (Margules et al., 2000). The negative ecological impacts of this habitat loss are expected to amplify as the industry expands (Osvaldo et al., 2000; Fairbanks et al., 2004). Growers and managers in some areas are adopting strategies that take into account the economic benefits of increased production as well as cost of ecological tradeoffs, such as the loss of water filtration capacity and soil fertility, which pose long-term expense to managers when they must be mechanically or chemically replaced.
NGOs and tradeoff assessment
Non-governmental organizations (NGOs), such as the South African-based Biodiversity in Wine Initiative facilitate land-use decision making that balances human needs and maintaining ecosystem integrity and function. Their emergence underscores the need to resolve the paradox of simultaneously attempting to conserve biodiversity, and maintain ecological services, and maximize the economic benefits of agricultural commodity exports.
Positive economic feedbacks
Economic incentives can be viewed as positive feedbacks, in which the monetary gains from exports create a greater incentive to further expand agricultural production. As production expands, the short-term gains spur further extensification, particularly in internationally competitive commodity markets such as wine grapes. Monitoring agencies may be able to mitigate the intensity of positive economic feedbacks by quantifying the costs and benefits of foregoing some production capacity to conserve areas of high diversity and unharvested biomass. Mitigation measures include educating land managers and policy makers of the long-term value of maintaining ecosystems that are not intensively managed for production and harvest.
Energetically inefficient agroecosystems
At the global scale, agricultural systems operate on a program of increasing inefficiency. For instance the United States currently exports 78 million tons of pistachios to Canada, while simultaneously importing 32 million tons of Canadian pistachios (Costa, 2007). This cycle of international trade belies the large energetic costs associated with commodity export agriculture and an additional tradeoff of selecting for high production at the expense of all other considerations. Ecological and energetic tradeoffs are often hard to measure because they are removed from the ecosystems they impact, or they have impacts that are geographically dispersed such as global climate change (Chapin et al., 2006).
Michael Pollan’s Botany of Desire emphasized the disproportionate amount of petroleum energy used to grow, package, and ship food commodities coast to coast. Pollan estimated that “the strawberry has five food calories of energy and requires 435 fossil fuel calories to ship it from California to New England” (Pollan, 2001). The ratio of petroleum energy to food calories is exceptionally high for specialty fruits and transnational agricultural commodities, but, on the whole, U.S. farms expend far more fossil fuel energy than the food calories they produce. Estimates made on the amount of food calories produced per calorie of fossil fuel energy used are between 2.3 and 3 in 1940. In 1974, the ratio was even (1:1), and today the ratio is near 3:1 for the average farm and as high as 10:1 for meat production or highly processed cereal grains (Manning, 2004).
Wes Jackson emphasized that drivers of high production are intrinsically linked to farmers’ need to achieve large volume harvests in order to recoup capital invested and other expenditures. As Odum’s framework suggested, exponentially increasing production capacity has associated ecological costs. According to Jackson et al. (1996) each bushel of Iowa corn produced costs us roughly one and a half bushels of top soil as a result of the tilling necessary for monocropping systems, a quantification of Odum’s observation regarding the interrelationship between losing ecosystem services when biomass, diversity, and later successional stages are eliminated.
Regional case study: California’s Sacramento Valley
Agricultural management in the Sacramento Valley increasingly emphasizes the importance of small locally owned farms, niche market for organics, and consumer education. Advocates use the term sustainable agriculture to distinguish economic, ecological and social approaches that are distinct from global-scale commodity agriculture. Many of the socio-economic arguments for the efficacy of a regional focus on agroecosystem management rest on “the assumption that sustainable agriculture is more labor-, information-, and management intensive…it is thought to favor smaller, family run farms over larger corporate farms” (Brodt et al., 2004: 76). Small and midsized farms are “more anchored to place by social and economic relationships” (Tolbert et al., 1998: 404; Jackson et al., 1996). These relationships may help to alleviate geographical separation from the ecological and energetic tradeoffs put forth by Chan et al. (2006), ultimately reducing long-term costs and losses of functional ecosystem connections.
Social capital in regional-scale agriculture
Social capital facilitates norms of reciprocity and trust, helping to link farmers with the broader community. Putnam (1995) and Coleman (1990) define social capital as “the set of resources inherent to interpersonal relationships and social organization that can be used to enhance cooperation and trust.” Consumers that have direct experience of agriculture or personal interactions with farmers can help build “communities of interest” around regional or local agriculture (Benbrook, 2001). In the Sacramento Valley, NGOs such as the Community Alliance for Family Farmers (CAFF) have facilitated education initiatives by tapping into communities of interest. CAFF’s “ Buy Fresh, Buy Local” campaigns emphasize the area’s unique attributes and educate consumers that their purchases help to sustain the local food shed. Feenstra (2004) highlights the Valley’s >100 area farmers’ markets and community supported agriculture (CSA) programs as cornerstones of the local food shed, which can be described as “a natural geographic area from which food comes and goes” or “the flow of food in a region.”
Advocates argue that maintaining viable markets for smaller, local farms and “eating within the food shed” reduce the need for conversion of native ecosystems for farmland by reducing consumer demand for international commodity products; the energetic inefficiencies and ecological costs transnational shipping incurs are also curtailed (Feenstra, 2004; Pollan, 2006). Regulatory policies, such as mitigation of development of agricultural land, are quantifiable effects of social capital and regional approach to agroecosystem management. Yolo County, CA, has a 2:1 mitigation requirement for the development of agricultural land; for every acre of agricultural land that is developed for other uses, two must be conserved. Helping to stem the conversion of native ecosystems into intensively managed agroecosystems on the county level (by assuring that farmland remains locally available) is one method of reducing the aggregate rate of land-use change at the global scale. The regional management focus underpinned by social capital may help to achieve the integrated reevaluation of perceived production needs Odum argued for. Future research may focus on identifying indicators that provide reliable, widely applicable guideposts to objectively assess and quantify the tradeoffs between ecosystems managed for production capacity and those managed for levels of biomass and diversity needed to sustain native ecosystems’ functional connections and services.
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