METHODSDefining and classifying ecosystem services for decision making
Introduction
Ecosystem services research has become an important area of investigation over the past decade. The number of papers addressing ecosystems services is rising exponentially (Fig. 1). The significance of the concept is witnessed by the publication of the Millennium Ecosystem Assessment (MA), a monumental work involving over 1300 scientists. One of the key results of the MA was the finding that globally 15 of the 24 ecosystem services investigated are in a state of decline (MA, 2005), and this is likely to have a large and negative impact on future human welfare. One of the clarion calls of the MA was for increased and concerted research on measuring, modeling and mapping ecosystem services, and assessing changes in their delivery with respect to human welfare (Millennium Ecosystem Assessment, Carpenter et al., 2006, Sachs and Reid, 2006).
The 1300-plus scientists have moved ecosystem services science considerably forward. One of the key MA documents subtitled “A Framework for Assessment,” clearly indicates that it is not intended to be a static document. Additionally, several lead authors have acknowledged the need to keep this as an evolving concept (see Carpenter et al., 2006, Sachs and Reid, 2006). To do this, the scientific community needs to frequently check the validity of early concepts, including how ecosystem services are defined, and how the concept can be utilized by a wide range of stakeholders including scientists, economists, practitioners, policy makers, land managers and environmental educators.
This requires a clear and consistent definition of what ecosystem services are and a wider understanding of key characteristics of ecosystems and the services they provide.
The MA opened a wider understanding and use of ecosystem services and offered an excellent heuristic and classification system. Despite its recent publication date, the MA classification of supporting, regulating, provisioning and cultural services is one of the most widely used. This classification is understandably not meant to fit all purposes, and this has been pointed out for contexts regarding environmental accounting, landscape management and valuation, for which alternative classifications have been proposed (Boyd and Banzhaf, 2007, Wallace, 2007, Fisher and Turner, 2008).
However, underlying the multiple ways in which ecosystem services can be packaged or classified, we suggest that there needs to be a clear, consistent and operational definition of what ecosystem services are. This is because a functional definition, widely agreed upon, would allow for meaningful comparisons across different projects, policy contexts, time and space (Boyd, 2007, Barbier, 2007). Such a definition would also provide us with boundaries for the characteristics we are interested in. For example, if we use the MA definition, i.e. benefits people obtain from ecosystems, then the characteristics of import include things outside of ecological systems such as imputed cultural meanings, recreation, and spiritual fulfillment.
However, if ecosystem services are defined as ecological phenomena, as below or as in Boyd and Banzhaf (2007), then the first role of science, to deliver information to society, becomes much more clear. In this vein, the first duty is to understand and relate the behaviors and characteristics of ecological systems. Some of the identified characteristics, along with the decision context or motivations for mobilizing ecosystem services, will inform an appropriate classification system for use, or rather a meaningful and transparent way to organize ecosystem services for use.
This paper argues that a classification system should be informed by 1) a clear and robust definition 2) the characteristics of the ecosystem or ecosystem services under investigation and 3) the decision context or motivation for which ecosystem services are being considered.
Fig. 2 demonstrates how we suggest that these various issues connect. First and foremost we suggest that clearly defining what ecosystem services are is important, at the very least so that (as stated above) meaningful comparisons and synergies can be made across projects, researchers etc. As pointed out by Boyd and Banzhaf (2007), GDP accounting was slow to deliver a consistent set of definitions and accounting methods, and to this day we still talk about production within national boundaries (GDP), and production by nationals of a country regardless of where it happens in political space (GNP). This type of evolution is likely to be the case with the ecosystem services concept.
Once we define ecosystem services then we can consider their characteristics and the characteristics of the systems from which they derive that are important for understanding their link with human welfare. Fig. 2 also suggests that we need to know something about the decision context or motivations for mobilizing ecosystem services research (e.g. spreading awareness, accounting systems, landscape management…). A brief example following Fig. 2 is such: we define ecosystem services to be about ecological phenomena (e.g. not cultural services which we see as very valuable benefits derived from ecosystems and services); we know that some ecosystems and functions can behave nonlinearly (characteristic); we are trying to decide how much upland forest to convert to a ski resort (decision context); we can classify our ecosystem services based on any (un)certainty about their functional response to this land conversion. Perhaps, at certain initial levels, a list of services that will behave in as linear response include genetic storage, pollination, carbon sequestration. A list of services that may change nonlinearly could include soil retention and water regulation. By classifying services in this way they can feed back into the decision process and perhaps suggest a precautionary approach or management strategy for soil retention and water regulation. The rest of this paper is used to flesh out Fig. 2 and expand its implications.
First we suggest a broad, yet operational, definition of ecosystem services (Section 2); identify some of the characteristics of ecosystems and the services they provide that might be important for classification schemes (Section 3); and provide examples of decision-making contexts which illustrate how any classification scheme needs to fit the end use for an investigation into ecosystem services (Section 4). We then offer some concluding thoughts on the future of ecosystem service research.
Section snippets
Defining ecosystem services
Humanity's reliance upon nature for welfare and survival is complete. The history of civilization is, at its most basic, a story of people trying to access resources and seek protection from the elements. Around 10,000 years ago when we began to domesticate nature, the story changed a bit. Through husbandry and agriculture we were managing nature's services more directly in order to increase productivity. In this way humans have always recognized the importance of what we now call ecosystem
Characteristics of ecosystems and ecosystem services
Once we have clearly defined ecosystem services, we can consider their characteristics, and the characteristics of the ecosystems that produce them. By understanding key characteristics we can better manage, maintain, restore or evaluate ecosystem services. For example by knowing that there are seasonal fluctuations in stream flows needed for irrigation we can prepare for this variability though water collection or better irrigation management. Below we discuss a few broad characteristics that
Classifications, decision contexts and motivations
There have been several efforts to classify ecosystem services (e.g. de Groot et al., 2002, Millennium Ecosystem Assessment, Wallace, 2007). The dynamic complexity of ecosystem processes and the innate characteristics of ecosystem services (some noted above) should have us thinking about several different types of classification schemes (Costanza, 2008). Any attempt to come up with a single or fundamental classification system should be approached with caution. Also, ecosystem services are
Conclusions
Ecosystem services research is a rapidly evolving field, and while the term itself may be relatively new, an understanding that nature provides services for human welfare goes back to the myth of Eden. In some respects it is still early days for concerted scientific research into ecosystem services. However, consistent and robust means of measuring, mapping, modeling, and valuing ecosystem services are beginning to emerge (Ricketts et al., 2004, Naidoo and Ricketts, 2006, Chan et al., 2006,
Acknowledgements
The initiation of this work came out of the Valuing Wild Nature workshop (University of East Anglia March 12–16th 2006) sponsored by the Royal Society for the Protection of Birds, Natural England, and the UK Government's Department for Environment, Food and Rural Affairs. Brendan Fisher was supported by RSPB and the Leverhulme Trust. We would like to thank Jim Boyd and Shuang Liu for commenting on earlier versions of the manuscript, and two anonymous referees for their suggestions which greatly
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