Agriculture, water, and ecosystems: avoiding the costs of going too far
Managing agriculture for multiple outputs. Increasing attention to ecosystem services provides an opportunity to emphasize multifunctionality within agroecosystems and the connectivity between and within agroecosystems and other ecosystems. It is often assumed that agricultural systems are managed only for optimal (or maximum) production of one ecosystem service, food, or fiber (figure 6.4). But agricultural systems can generate other ecosystem services, and we need to improve our capacity to assess, quantify, and value these as well. Encouraging multiple benefits from these systems can generate synergies that result in the wider distribution of benefits across more people and sectors. Ecosystem- based approaches to water management need not constrain agricultural development but can be points of convergence for social equity, poverty reduction, resource conservation, and international concerns for global food security, biodiversity conservation, and carbon sequestration (see chapter 15 on land). Ecosystem-based approaches aim to maintain and where possible enhance diversity and to build the ecological resilience of the agricultural landscape as well as of ecosystems altered by agriculture (box 6.11).
e concept of multifunctional agriculture is not new; it has long been practiced in
many forms and combinations. Integrated pest management is one way to manage a whole landscape in order to sustain an ecosystem service (pest control) that enhances agricultural production. is type of regional management requires integrated approaches based on an ecological understanding of fragmentation and landscape heterogeneity (Cumming and Spiesman 2006). Hydrological understanding is also important. Studies have shown that it is possible to control insect outbreaks by timing irrigation events (Lansing 1991) and that
Some basic principles for maintaining ecosystem resilience
The resilience perspective shifts from policies that aspire to control change in systems assumed to be stable to policies to manage the capacity of social-ecological systems to cope with, adapt to, and shape change (Berkes, Colding, and Folke 2003). Managing for resilience enhances the likelihood of sustaining development in changing environments where the future is unpredictable.
Variability, disturbance, and change are important components of an ecosystem. For example, when variability in river ows is altered, marked changes in ecosystem functions can be expected (Richter and others 2003). Wetting and drying of soils can be important for the resilience of ecosystem functions, such as pest control and nutrient retention in wetlands. Exactly what level of variability to maintain and when variability is site specic are areas of intense research (Richter and others 2003). Maintaining diversity has been shown to be important for building ecosystem resilience, in particular for maintaining functional and response diversity (Elmqvist and others 2003; MEA 2005c). Responses should therefore seek to maintain and enhance diversity in ecosystems and across broader land- scapes while maintaining food production.
The driving variables behind the functioning of ecosystems tend to have slower dynamics than those that support the ecosystem services generated from that system (Carpenter and Turner 2000). Therefore, the monitoring of long-term ecosystem performance should cover the productivity of the ecosystem and the crucial variables that enable production. This is particularly evident when monitor- ing the productivity of croplands. Harvested yields are an important measure, but they may not tell the full story. Long-term productivity likely depends on slower variables, such as the accumulation and decomposition of soil organic matter.