Agriculture, water, and ecosystems: avoiding the costs of going too far
Resilience and the increased risk of rapid regime shifts in ecosystems
Ecosystems change and evolve, with disturbance now seen as an inherent component of ecosystem processes [well established]. The speed of change in many ecosystems has, however, increased rapidly, and there is now concern that large-scale changes will increase the vulnerability of some ecosystems to water-related agricultural activities. Ecosystems are complex adaptive systems (Levin 1999), with nonlinear dynamics and thresholds between different “stable states.” Nonlinear changes are sometimes abrupt and large, and they may be difcult, expensive, or impossible to reverse. The increased likelihood of nonlinear changes stems from drivers of ecosystem change that adversely affect the resilience of an ecosystem, its capacity to absorb disturbance, undergo change, and still retain essentially the same function, structure, identity, and feedbacks (Gunderson and Holling 2002; Carpenter and others 2001) and provide components for renewal and reorganization (Gunderson and Holling 2002).
Variability and exibility are needed to maintain ecosystem resilience. Attempts to stabilize sys- tems in some perceived optimal state, whether for conservation or production, have often reduced long-term resilience, making the system more vulnerable to change (Holling and Meffe 1996). While today’s agricultural systems are able to better deal with local and small-scale variability, the simpli-
cations of landscapes and reduction of other ecosystem services have decreased the capacity of
agricultural systems and other ecosystems to cope with larger scale and more complex dynamics through reduced ecosystem resilience locally and across scales (Gunderson and Holling 2002).
Little is yet known about how to estimate resilience and detect thresholds before regime shifts occur (Fernandez and others 2002). Better mechanisms to monitor regime shifts include the iden- tication and monitoring of slowly changing variables (Carpenter and Turner 2000) and measurable “surrogates of resilience” (Bennett, Cumming, and Peterson 2005; Cumming and others 2005).
Societal responses and opportunities
e negative effects of past agricultural management on ecosystem services and the need
to produce more food for growing populations provide an unparalleled challenge. Meet- ing this challenge requires large-scale investments to improve agricultural management practices, increase the availability of techniques to minimize adverse ecological impacts, enhance our understanding of ecosystem-agriculture interactions, and reduce poverty and social inequities, including issues of gender, health, and education that affect ecosystem management decisions.
In presenting possible responses for meeting this challenge, we emphasize several ecological outcomes that we consider to be critical in this effort: maintenance or rehabili- tation of the ecological connectivity, heterogeneity, and resilience in the landscape, which in turn implies maintenance or rehabilitation of the biodiversity that characterizes the landscape. We focus on integration and awareness of the negative consequences of choices in terms of the tradeoffs between food production and other ecosystem services. We do not propose specific responses for specific ecosystems or locations, although we aim to help national and local decisionmaking with a framework for addressing some of these issues. Many of the responses outlined are dependent on effective governance measures and policies that support sustainable development with a balance of ecological and social