Policymakers and resource managers often frame ecosystem services management challenges as a matter of protecting natural areas outside of cities. Assuring good stewardship of nature’s services in rural areas is indeed crucial but is only part of the solution. Over 50 percent of the world’s human population now resides in urban areas, a figure projected to grow to 66 percent by 2050, with huge impacts in developing countries. The New York Times reported in 2007 that, “from now to 2030, the world will need to build the equivalent of a city of one million people in developing countries every five days.”1
This unprecedented demographic shift concentrates pressure on ecosystem services in and around urbanizing regions. Such higher-density development presents challenges and opportunities for management of the ecosystem services that sustain healthy living environments and vibrant commerce. For example, growing cities concentrate large amounts of water pollution and other wastes, but that centralization may result in lower treatment costs than if the damages accumulated in rural areas with vulnerable natural ecosystems. Understanding the dynamics and feedback effects of these systems that span human and natural components is paramount. In this article we suggest a transdisciplinary approach to effectively manage ecosystems that support urbanizing areas.2–5
Our framework posits that ecological functioning declines across a continuum from natural ecosystems, such as wilderness areas; to intermediate services, such as urban green spaces; to built replacement services, such as wastewater treatment plants (see Figure 1).6 Natural ecosystems provide important services if left largely unaffected by human development; these services often are uncounted by markets and in policy decisions.7 Intermediate and replacement services require modifications of formerly natural ecosystems with diminished ecological value. While several studies have examined ecosystem services in natural environments, few have examined to what degree those services in nonhuman-dominated landscapes are needed to complement or substitute for those lost from human-dominated environments, such as urbanizing areas. To do so, the social and economic dimensions of ecosystem services values should be integrated with ecological values as discussed below.
Ecosystem Fundamentals
Ecological systems deliver a variety of ecosystem services to human society, including provisioning (e.g., timber), supporting (e.g., soil formation), regulating (e.g., water filtration), and cultural (e.g., recreation) services.8 For example, a natural soil formed over centuries has the ability to adsorb air- and waterborne contaminants, reduce rainfall acidity, moderate the impact of high-intensity storms on streams, and act as a fertile substrate for plants that provide animal habitat as well as food and fiber for human populations. Human impacts on ecosystems include harvesting biological populations (e.g., logging, fishing) and converting landscapes through alterations of substrate (e.g., paving, trawling).9 Human impacts can exceed most natural disturbances in magnitude, especially when ecosystem surfaces are altered to the extent that natural successional and recovery processes are no longer possible, resulting in a loss of system resilience. Agricultural or aquacultural conversions of landscapes often result in substitution of ecosystem services, where one service is enhanced (e.g., provisioning gains in crops or fisheries) at the expense of other ecosystem services (e.g., losses of supporting soil formation or of buffering coastal habitats) (see Box 1 for a freshwater case). Urbanization conversions of landscapes often result in outright losses of ecosystem services (see Box 2).
Effective ecosystem services management depends on how well humans work in concert with how ecosystems naturally function. Ecosystems require continuous inputs of energy via photosynthesis in plants and naturally occurring material inputs such as nitrogen and calcium. Also, ecosystems naturally experience change, known as succession, spanning from recently disturbed areas (i.e., early succession) to mature areas (i.e., late succession, characterized, for example, by old-growth forests). A key question in management is how much of the original natural functioning and resultant services provided by an ecosystem are maintained or at least substituted (see Figure 1). As the case studies indicate (see Boxes 1–4), preserving a net positive balance requires a careful assessment of ecological function along with consideration of social and economic factors. A critical challenge in effective ecosystem services management, particularly in urban areas, is a better synthesis of socioecological relationships and a more transdisciplinary approach, as discussed in the next section.10
Box 1: Restoring a Natural Ecosystem
Clean Water Services (CWS), a public water resources utility in a rapidly urbanizing region within metropolitan Portland, Oregon, operates four wastewater treatment facilities, releasing treated effluent into streams within the Tualatin River watershed.1 The effluent from the treatment plants enters the river at temperatures high enough to impair resident fish species downstream. The environmental quality authority, the Oregon Department of Environmental Quality (DEQ), requires that CWS reduce the temperature of its discharges. CWS’s permits to discharge into the river depend on its ability to meet the proscribed temperature reductions. The utility’s service population and the regional economy served by CWS are projected to grow dramatically in the next 20 years, with consequent growth in demands on CWS to treat wastewater. This growth, not surprisingly, adds to the need to find ways to combat increasing water temperatures in the river.
As CWS managers were deciding how to achieve the necessary temperature reductions, they were also confronted with environmental issues of preserving/restoring endangered and threatened salmon habitat and meeting Oregon’s land-use requirements. The complexity of dealing with these interacting issues prompted management to consider the water temperature issue from a systems perspective. Instead of simply trying to find ways to mechanically cool the effluent as it entered the river—the traditional method of addressing this problem—CWS personnel considered the real goal of the regulations: to create water conditions that meet the needs of fish and humans downstream from the treatment plants. With this in mind, CWS staff considered their options. To comply with temperature requirements, CWS could construct a new concrete and metal cooling facility, or it could restore the ecosystem above the two treatment plants and use naturally occurring regulating ecosystem services. This latter option entailed planting shade trees, shrubs, and native grasses along the banks of the river for natural cooling downstream. Either option would provide the cooling necessary to meet the needs of the fish and the requirements of DEQ, enabling CWS to obtain the permits needed to operate its wastewater treatment facilities.
In analyzing these two feasible options, the utility examined costs and benefits through both a financial and an environmental lens. The capital cost of building the required cooling plant for the expected demand exceeded U.S.$60 million, with annual operating costs of over U.S.$2 million. The present value total cost of the cooling plant computed to at least U.S.$70 million. There was a clear environmental cost as well, from the carbon footprint of building and operating the plant. The benefits from the cooling plant would be effective cooling of the effluent, resulting in acceptable review by the governing authorities and a relatively risk-free issuance of a permit to practice. There were no other environmental benefits identified.
The cost of planting native shrubs and trees along approximately 35 miles of upstream riverbank, plus the annual payments to landowners for conservation easements to guarantee that the plantings would not be damaged by agricultural use, was estimated at a present value of about U.S.$5 million. For businesses such as CWS, the risk of losing permits creates considerable concern, which translates into a real, but intangible, cost. In this case, CWS worked with the governing authorities to demonstrate that improving the ecosystem above the treatment plants would be effective. The utility convinced the authorities that the plantings and management of the upstream lands would provide the required shading to the river, cooling it sufficiently, in a measurable manner, and thus would meet the permitting requirements. The resulting plantings and additional ecosystem improvements have in fact resulted in a variety of additional ecosystem services benefits that continue to accrue.2 More than 1.6 million native trees and shrubs were planted between 2004 and 2008, generating total thermal credits of 295 million kilocalories per day.
In addition to the significant cost savings of restoring a native ecosystem rather than constructing a mechanized fix to the wastewater temperature problem, the restored ecosystem provides services such as salmon habitat, upland scrub habitat, carbon sequestration, increased biodiversity, and recreation opportunities. Although functioning markets for many of these services are currently embryonic or nonexistent, the market mechanisms and protocols are being created and piloted by the utility and affiliated organizations. The critical roles of these overlooked and neglected ecosystem services will exert more influence on public and private management decisions as we improve our capacity to value them via markets or by other means.3
