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Capacity, Pressure, Demand, and Flow:
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A conceptual framework for analyzing ecosystem service provision and delivery
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Amy M. Villamagnaa*, Paul L. Angermeierb, Elena M. Bennettc
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Department of Fish and Wildlife Conservation, Virginia Tech, Blacksburg, VA 24061-
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0321, USA *Corresponding author, amv@vt.edu; b U.S. Geological Survey, Virginia
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Cooperative Fish and Wildlife Research Unit1, Virginia Tech, Blacksburg, VA 24061-
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0321, USA biota@vt.edu; c Department of Natural Resource Sciences and McGill School
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of Environment, McGill University, Montreal, Quebec, CANADA
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elena.bennett@mcgill.ca
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ABSTRACT
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Ecosystem services provide an instinctive way to understand the trade-offs associated with
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natural resource management. However, despite their apparent usefulness, several hurdles have
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prevented ecosystem services from becoming deeply embedded in environmental decision-
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making. Ecosystem service studies vary widely in focal services, geographic extent, and in
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methods for defining and measuring services. Dissent among scientists on basic terminology and
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approaches to evaluating ecosystem services create difficulties for those trying to incorporate
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ecosystem services into decision-making. To facilitate clearer comparison among recent studies,
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we provide a synthesis of common terminology and explain a rationale and framework for
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distinguishing among the components of ecosystem service delivery, including: an ecosystem’s
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capacity to produce services; ecological pressures that interfere with an ecosystem’s ability to
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provide the service; societal demand for the service; and flow of the service to people. We
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discuss how interpretation and measurement of these four components can differ among
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provisioning, regulating, and cultural services. Our flexible framework treats service capacity,
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ecological pressure, demand, and flow as separate but interactive entities to improve our ability
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to evaluate the sustainability of service provision and to help guide management decisions. We
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consider ecosystem service provision to be sustainable when demand is met without decreasing
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capacity for future provision of that service or causing undesirable declines in other services.
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When ecosystem service demand exceeds ecosystem capacity to provide services, society can
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choose to enhance natural capacity, decrease demand and/or ecological pressure, or invest in a
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technological substitute. Because regulating services are frequently overlooked in environmental
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assessments, we provide a more detailed examination of regulating services and propose a novel
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method for quantifying the flow of regulating services based on estimates of ecological work.
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We anticipate that our synthesis and framework will reduce inconsistency and facilitate
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coherence across analyses of ecosystem services, thereby increasing their utility in
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environmental decision-making.
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KEYWORDS: ecological pressure, ecosystem services, inventory and assessment, regulating
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services, service capacity, service demand, service flow
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1. Introduction
Ecosystem services (ES) have great potential to influence environmental decisions
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because they link ecosystem functions and conditions to anthropocentric interests that resonate
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with a broad spectrum of people. ES provide new currencies, often not represented in markets,
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for understanding the tradeoffs associated with natural resource management (Raudseppe-Hearne
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et al., 2010; Chan et al., 2012). Because of this, efforts to assess and inventory ES have been
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extensive (Peterson et al., 2003; MA, 2005; Tallis and Polasky, 2011; Burkhard et al., 2012);
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however, several hurdles have prevented ES from becoming deeply embedded in environmental
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decision-making (Daily et al., 2009; de Groot et al., 2010). However, a fundamental hurdle in
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using ES in decision-making is the inconsistency with which scientists have conceptualized
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delivery of ES to society (Tallis et al., 2012). Recent strides towards greater consideration of ES
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have been made in the European Union (TEEB, 2010; European Commission, 2011; Hauck et
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al., 2013); however, use of the ES concepts in policy-making remains limited (Fisher et al.,
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2009) and many questions persist over how ES relate to each other, how ecosystems produce
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services, how to consistently quantify ES flows, and how changes in landscapes are likely to
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affect future delivery of ES (Chan et al., 2006; Carpenter et al., 2009; de Groot et al., 2010;
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Hauck et al., 2013).
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Despite real differences, few researchers distinguish among the capacity of an ecosystem
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to produce a service, actual production or use of that service, societal demand for that service,
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and the natural and anthropogenic pressures on the service (Burkhard et al., 2012; Nedkov and
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Burkhard, 2012; van Oudenhoven et al., 2012). For example, the capacity of an ecosystem to
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generate services differs from the actual services delivered to society. A farm may produce less
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food than it could under different management choices, or a wetland may have greater capacity
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to filter nitrogen than is ultimately needed in the system. The benefits actually delivered depend
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not only on an ecosystem’s capacity to provide services, but also on demand for these services,
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which is, in turn, driven by biophysical setting, population size, cultural preferences, and the
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perceived value of the service. Demand for an ES can change independently of capacity, and
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vice versa. Thus, measurements of any one component of ES delivery cannot capture the full ES
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dynamic from production to benefit (Fig. 1). Despite this, studies that measure only one or two
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components of ES provision are common (Tallis et al., 2012).
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Frameworks for conceptualizing and analyzing ES are rapidly evolving (Boyd and
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Banzhaf, 2007; Wallace, 2007; Costanza, 2008; de Groot et al., 2010; Nedkov and Burkhard,
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2012; van Oudenhoven et al., 2012), with little consensus on which framework or analytical
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products are most useful for environmental decision-makers. Some recent conceptual
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frameworks distinguish components of ES delivery (e.g. demand; Tallis et al., 2012), but
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definitions of components and relations among them differ widely across authors. For example,
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capacity has also been referred to as potential supply (Burkhard et al., 2012), ecosystem potential
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(van Oudenhoven et al., 2012), stocks of nature, and ES per se (Norgaard, 2009; Layke, 2009),
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yet the basic concept behind each term is the same. In contrast, there seems to be weaker
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consensus on how service flows, the benefits actually delivered to people, are measured or
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defined (Fig. 1). Terminology often differs along an ecology-economics continuum, ranging
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from economic concepts such as benefits (Wallace, 2007; Balmford et al., 2008) or supply (Hein
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et al., 2006) to ecological concepts like performance indicators (de Groot et al., 2010) or flow
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(Beier et al., 2009; Layke 2009). Moreover, some studies focus on the mechanics of ES delivery
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(Bagstad et al., 2012) while others emphasize the ecosystem properties and processes that
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influence the service production (de Groot et al., 2010; van Oudenhoven et al., 2012). While the
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breadth of approaches has surely furthered the exploration of services and has likely enhanced
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our ability to evaluate services, the disparate terminology and subtle differences among
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frameworks can inhibit managers and decision-makers from choosing an approach appropriate to
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their needs. To enhance our ability to quantify, map, and ultimately make ES information more
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accessible to decision-makers, we must acknowledge the inherent differences among ES types
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(Table 1), the dynamic process by which ES are produced (Fig. 1), and how ES benefit people
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(Carpenter et al., 2009; Bagstad et al., 2012; Chan et al., 2012). The key is finding a flexible and
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adaptive approach that still allows consistency while avoiding rigid, one-size-fits-all frameworks.
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Ecosystem services are categorized in multiple ways, with different categories being
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amenable to different analytical approaches and providing distinctive societal benefits (MA,
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2005). However, incorporating differences among service categories in ES assessments while
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acknowledging their interconnectedness has been difficult. Some researchers group ES based on
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their contribution to human well-being: services that directly benefit people (e.g. water supply)
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are considered final or end services while many regulating and supporting services that
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contribute to provision of final services are considered to be intermediate services. Intermediate
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services are often excluded from economic valuations to avoid double counting (Boyd and
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Banzhaf, 2007; Fisher and Turner, 2008; Wallace, 2008), but, in some cases, changes in
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intermediate service provision are central to the potential societal trade-offs associated with
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environmental management decisions. Limiting ES assessments to final services precludes
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considering environmental and economic trade-offs, often resulting in the undervaluation of
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services across the board (Keeler et al., 2012). Improving ES assessments requires development
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of methods for quantifying intermediate or regulating service capacity, demand, and flow in
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biophysical terms (Layke, 2009; Chan et al., 2012; Keeler et al., 2012).
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To help advance a common language associated with ES assessments and further the
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application of ES frameworks, we reviewed and synthesized the literature on basic components
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of ES delivery. From this synthesis we promote a framework in which an ES delivery model
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comprises four distinct components: capacity (i.e. the potential to provide a service), ecological
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pressures (i.e. anthropogenic and natural stressors on ES provision), demand (i.e. the amount of
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service required or desired by society), and flow (i.e. the actual production of a service
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experienced by people). Second, we discuss how the interpretation and measurement of these
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components of ES differ among provisioning, regulating, and cultural ES and how measures of
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each can be used to evaluate sustainability. Third, we discuss a new approach to evaluate
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capacity, ecological pressure, demand, and flow specifically for regulating services (RS), which
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are often left out of ES assessments due to complexities associated with quantifying them. To
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strengthen the methodology for assessing RS, we describe how to quantify RS flow using
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estimates of ecological pressure and environmental quality.
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2. Distinguishing service capacity, pressure, demand, and flow
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Separately measuring the components of ES delivery adds clarity to ES analyses and can
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enhance integration into environmental planning and development. By distinguishing among ES
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capacity, demand, ecological pressures, and flow we can 1) assess the current and future
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biophysical capacity of an area to produce ES, 2) evaluate the sustainability of ES use under
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different scenarios of ES demand, pressure, and capacity, and 3) examine how ES demand and
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ecological pressures influence biophysical capacity via feedback loops in which pressure may
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exceed ecological thresholds (Carpenter et al., 2009). By comparing measures of current and
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future capacity, ecological pressures, demand, and flow planners can evaluate whether a) the
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needs of people can be met by existing ecosystem properties and processes, b) technological
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substitutes are needed to supplement service production, c) ES flows will be equitable, and d) the
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flow of services is sustainable (i.e. doesn’t degrade ES capacity).
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2.1. Service capacity
Service capacity is an ecosystem’s potential to deliver services based on biophysical
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properties, social conditions, and ecological functions (Cairns, 1997; Chan et al., 2006; 2011;
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Egoh et al., 2008; Daily et al., 2009; van Oudenhoven et al., 2012). ES capacity is site- and time-
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specific, but not static; capacity responds to natural or anthropogenic changes over time and
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space. Land use and human population changes have an acute effect on ES capacity as well as
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ES demand, ecological pressures and ES flows (Fig. 2; also Burkhard et al., 2012; van
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Oudenhoven et al., 2012). Capacity can be measured and mapped by integrating the natural and
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anthropogenic factors that influence the ecological properties and functions that provide services
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regardless of how many people use or benefit from the services in question (Table 1).
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Provisioning service capacity is typically measured directly by ecosystem properties (e.g.,
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volume of water supply). Although more difficult to measure, cultural service capacity depends
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on a mix of biophysical (e.g. climate, topography, presence of key species) as well as
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anthropogenic conditions (e.g. accessibility by humans, site management actions; Villamagna et
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al., in review). Capacity of an ecosystem to provide regulating services is also challenging to
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measure. Regulating service capacity tends to comprise several interconnected ecosystem
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processes that each rely on a suite of ecosystem properties (Fig. 3). Thus measuring regulating
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service capacity requires extensive knowledge of ecological processes, understanding of
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ecological and hydrologic processes, process-based models and their limitations (e.g. Revised
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Soil Loss Equation), and/or extensive field data .
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2.2. Ecological pressure
Ecological pressures are biophysical influences that interfere with an ecosystem’s ability
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to provide the service. They do so by increasing the work (i.e. effort) needed to provide the
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service or by reducing an ecosystem’s capacity to deliver service (MA, 2005; WRI, 2012).
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Ecological work includes the processes that generate the service and are discussed further in
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sections 2.4 and 4.2. Pressures make it more difficult for an ecosystem to meet societal demand
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for that service (see section 2.3) and sustained or extreme pressures can alter the future capacity
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of an ecosystem to deliver services (Carpenter et al., 2009). Pressures on ES can be natural, like
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periodic weather fluctuations, or anthropogenic, like increases in impervious surfaces. The
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source of the pressure can be related to overuse, like overfishing or crowding in recreation areas
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(Fig. 1), or it can be a by-product of ES trade-offs, like aquatic nutrient inputs from agricultural
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production. The World Resources Institute (WRI) manages an online database on ES indicators
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including direct and indirect drivers and service pressures (WRI, 2012). Our use of “pressure”
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varies slightly from that of the WRI in that we include direct drivers as service pressures if they
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are measured in the same units as the flow of the service (e.g. nutrient inputs conveyed through
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fertilizers and changes in land cover).
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2.3. Service demand
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Demand for ES, the amount of service desired by society, has been measured by a variety
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of indicators (Table 1). Human population density combined with average consumption rates is a
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common indicator (Burkhard et al., 2012; Nedkov and Burkhard, 2012), especially for services
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that directly impact human well-being, such as water supply or crop production. For many
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provisioning services, demand is concisely represented by market prices. For experience-based
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cultural services, the number of people wanting to experience the ES (e.g. visitors to a park) can
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indicate demand. Since RS produce or maintain desirable environmental conditions, societal
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demand should be expressed as the amount of regulation needed to meet a desired end condition
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(e.g. the percentage reduction needed to meet numeric criteria for a pollutant). Estimating RS
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demand is inherently challenging because it requires information about desired end conditions as
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well as the ecological pressures or inputs needing regulation. To date, few assessments have
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quantified RS demand biophysically. Instead, RS demand has been measured in terms of human
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population (Burkhard et al., 2012; Nedkov and Burkhard, 2012), which is weakly related to the
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amount of regulation actually occurring.
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For all ES, demand -- an outcome of socio-cultural preferences -- can exceed capacity,
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but capacity ultimately sets the limit on long-term service provision. Burkhard et al. (2012) and
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Nedkov and Burkhard (2012) found that demand for services as measured by population density
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of beneficiaries largely exceeds service capacity in urban areas, whereas the opposite is true in
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less-populated rural areas. While demand for provisioning and cultural services can be met by
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moving resources or people, demand for RS must often be met locally. Sometimes this demand
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can be met by a technological substitute, but often the substitute meets a single demand rather
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than the suite of demands that might be met by natural systems. For example, ecosystems with
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high capacity to purify water provide clean drinking water, healthy aquatic habitats, and sources
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of aquatic recreation (Keeler et al., 2012), but water treatment plants may only address the
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drinking water demand.
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2.4. Service flow
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We consider service flow to be the service actually received by people, which can be
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measured directly as the amount of a service delivered, or indirectly as the number of
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beneficiaries served. Total service flow can be quantified as the service delivery per beneficiary
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multiplied by the number of beneficiaries (Table 1). Like other components of the ES delivery
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process, we suggest incorporating differences among ES types into measurements of service
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flow (Table 1). For provisioning services, the conventional metric of service flow is the
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equivalent of the end good (e.g. timber production). Cultural services are similar to provisioning
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in that the flow of cultural service is conventionally measured in terms of the duration and
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quality of the experience with nature. Although inherently challenging to analyze because they
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are individualistic, difficult to aggregate, and sometimes influenced by social or moral factors
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(Chan et al., 2012), many cultural service flows are estimated using market and non-market
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techniques. In contrast, regulating services lack a clear end product that is tractable or
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commonly represented in markets. Instead, environmental quality has been adopted as a
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convenient metric of service flow and ecosystem state (Dale and Polasky, 2007; Martinez et al.,
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2009). However, simply measuring environmental quality does not necessarily convey the
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amount of ecological work or regulation that has occurred because the amount of ecological
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pressure on the ecosystem itself and the capacity to regulate also play a role. Environmental
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quality is the result of multiple services, regulating and provisioning, working against ecological
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pressures. Instead, we propose that the flow of a regulating service be measured in terms of the
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ecological work required to mitigate pressures and deliver the service demanded. We further
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discuss ecological work in measures of regulating service flow in section 4.2.
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While service capacity is site-specific, service flow is not limited to the site of
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production. Consider downstream benefits of clean water from upstream soil or nutrient
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retention. Where benefits can be experienced, given natural and anthropogenic pathways, is the
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benefit zone (Bagstad et al., 2012) and the people within the benefit zone are potential
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beneficiaries (Hein et al., 2006; Boyd and Banzhaf, 2007; Johnston and Russell, 2011; Martin-
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López et al., 2011). The proximity and capacity of ES sources and pathways defines the potential
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benefit zone, but natural and anthropogenic connectivity across landscapes influences
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spatiotemporal patterns of ES flow (Fig. 4; also Fisher et al., 2008; Bagstad et al., 2012).
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Moreover, some services are passively delivered to beneficiaries (e.g. clean air), while others
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require additional capital inputs on the part of the beneficiary (e.g. financial or physical capacity
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to access recreation services). Sometimes long-distance ES flows are fundamentally
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asymmetrical, creating social inequity in terms of the human well-being derived from ES
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management (Carpenter et al., 2009; Tallis et al., 2012).
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The terms and methods used to describe ES flow are especially wide-ranging relative to
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other components of ES delivery (Fig. 1). Although service flow represents the actual delivery of
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services and capacity represents the potential production of services, these concepts are
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sometimes used interchangeably (Layke, 2009), which can lead to misinterpretations of ES
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condition that affect decision-making. Service flow is an important measure of current ES
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delivery, whereas capacity provides a measure of the potential of the system. Flow and capacity,
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and their measures, must be consistently distinguished in order to accurately evaluate changes in
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service delivery over time and to identify areas of potential ES production in the future.
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Recognizing the differences between ES capacity and ES flow is an important step towards
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better understanding how changes in policy and management can affect ES values accruing to
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beneficiaries.
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3. Service delivery and sustainability
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The benefit of the conceptual framework we have laid out here is that distinguishing
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among measures of ES capacity, demand, pressure, and flow enables assessment of ecological
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sustainability and identification of key trade-offs (McDonald, 2009). Given that areas of high ES
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capacity and flow are often spatially mis-matched and that ES demand is influenced by many
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factors extraneous to service production (e.g. technological substitutes for ES, cultural values,
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and behavioral norms), quantifying ES components separately is an important step towards
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enhancing the ability of ES assessments to inform environmental decision-making. Spatially
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explicit ES budgets, the comparison of ES demand and capacity, can identify areas where
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technological substitutes or additional capital inputs will be needed to meet demand, and,
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likewise, areas where greater development and ES flow can be supported. ES flow is sustainable
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when demand is met by flow without decreasing capacity for future provision of that service
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(Fig. 1). ES flow is not sustainable when demand cannot be met by current capacity or when
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meeting demand causes undesirable declines in other services or in the future provision of the
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same service. For example, the flow of water purification services from a watershed would be
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considered unsustainable if the quality of the water produced consistently failed to meet stated
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criteria or the only way to meet those criteria was to significantly reduce food production.
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Trade-off analyses (Rodríguez et al., 2006; Daily et al., 2009; Raudsepp-Hearne et al.,
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2010) can help assess landscape-level ES sustainability. Prolonged periods of excess ecological
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pressure or overuse may shift ecosystem functions in ways that permanently alter ES capacity
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and delivery (Scheffer and Carpenter, 2003; MA, 2005). For example, protracted over-
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exploitation of tree, fish, and game populations decreases stocks and regenerative capacity of
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provisioning services (Hilborn et al., 1995; Larkin, 2000). When ES demand exceeds ecosystem
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capacity to provide services, society generally has three choices to avoid environmental damage
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and decreases in human well-being. First, people can enhance the system’s natural capacity to
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provide the services demanded, for example by applying fertilizers to increase food production.
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Second, people can recognize that supply is limited and reduce their demand appropriately.
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Third, people can invest in technology to help avoid the outcomes of diminished services. For
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example, we build dams, levees, and seawalls to reduce flood damage when landscapes cannot
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adequately modulate flood magnitude and frequency. While some technological solutions
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address a single service (e.g. water treatment plant) and fail to restore all potential benefits from
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a non-degraded system (e.g. habitat provision), others create novel ecosystems that enhance
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multiple services (e.g. a reservoir provides water supply, flood regulation, and recreation). In
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contrast, management choices can negatively impact the capacity of other services (Bennett et
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al., 2009) and a change in the flow of one service can greatly influence the ecological pressures
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on another service (Rodríguez et al., 2006; Barbier, 2009). Given the complex interactions
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among services, understanding ES trade-offs based on analyses that quantify capacity, demand,
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pressure, and flow are potentially valuable contributions of ES science to environmental
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decision-making.
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4. Moving forward with regulating services
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We suggest that distinguishing among the four components of ES delivery will provide
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planners with better information for decision-making. To successfully integrate this multi-
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component framework into ES assessments, we must enhance our understanding of how RS
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function and develop stronger methods for quantifying the demand for and flow of RS.
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Regulating services are integral to the delivery of provisioning and cultural services, yet RS are
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declining globally (MA, 2005; Carpenter et al., 2009). Regulating services are process-driven
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and, unfortunately, the data needed to directly measure their condition are often unavailable at
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scales large enough to support policy-making (Layke, 2009). Below, we review how RS differ
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from other service types and how this impacts the way we should quantify the components of
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RS.
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4.1. Regulating services are inherently different
Regulating services are distinct in that they often exert significant influence on the
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capacity to provide other services (de Groot et al., 2002; Boyd and Banzhaf ,2007), but direct
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impacts of RS on human well-being can be difficult to measure (Keeler et al., 2012). Even
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though RS provide important benefits for humans (e.g. water and air purification, drought or
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flood control, and regulation of disease), they tend to change slowly and are thus less amenable
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to typical scientific study. Few comprehensive and reliable ecological indicators are monitored
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for RS (Layke, 2009), which makes their value difficult to express in biophysical or monetary
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units. In addition, without market prices as indicators of their supply and demand, changes in
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capacity may go largely unnoticed (Cairns, 1997). Often, the value of RS is not apparent until the
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declines cause problems for other, more commonly measured services (e.g. floods or droughts
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affecting agricultural production). Together, the lack of economic and biophysical evaluations
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leads to the general undervaluation of RS and their absence in many planning decisions.
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4.2. Measuring demand for and flow of regulating services
Regulating services help maintain environmental quality within socially desirable
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ranges. The amount of RS delivered will vary among ecosystems depending on ecological and
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social pressures and capacities. Based on our four component framework, measuring regulating
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service flow requires information about both ecological pressures on the ecosystem providing the
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service and societal demand for the service itself. However, environmental quality (e.g. water
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quality) is often used as an indicator of regulating service flow (Dale and Polasky, 2007;
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Martinez et al., 2009; Shibu, 2009). Key strengths of using environmental quality as a proxy for
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some RS is that it is readily measured, meaningful to society, and changes in quality can be
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expressed in economic terms through market and non-market valuation (Farber et al., 2006).
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However, environmental quality is not equal to the capacity, pressure, demand, or flow of the
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service; instead it depends on the service capacity, relative pressure on the ecosystem and service
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processes, and for some, the flow of other services (e.g. nitrogen regulation is affected by
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stormwater regulation).
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In real landscapes, high environmental quality may be the result of high capacity to
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regulate anthropogenic stress or weak ecological pressures. High-capacity systems are capable of
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greater ecological work to regulate pressures, resulting in slower or less change in environmental
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quality (i.e. more regulation). A system with no (or very low) capacity to regulate (Fig. 5A)
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experiences quick decline in environmental quality (y axis) with increases in ecological pressure
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(x axis), while systems with higher capacity (Fig. 4B) can maintain acceptable environmental
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quality under great ecological pressure. Similarly, systems with identical capacity can differ in
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environmental quality due to differences in ecological pressures. Consider two watersheds in
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which water quality is equal and meets societal standards (i.e. demand), but differ in contaminant
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loading. One receives heavy nutrient loading as it flows through a mixed crop-forest landscape
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with fertilizer inputs while the other flows through a similar landscape mosaic without fertilizer.
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Although downstream nutrient concentrations are similar, ecological pressures differ markedly
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and the ecological work occurring is greater in the fertilized watershed. Simply using ambient
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water quality as a surrogate for RS flow cannot distinguish these two systems since it not only
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ignores the relationship between ES capacity and pressure, but does not differentiate among the
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multiple processes that affect water quality (e.g. filtration, sedimentation, volatilization, plant
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uptake; Fig.3).
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Instead of using environmental quality as an indicator of RS flow, we propose estimating
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the ecological work performed as the difference between ecological pressures and measured
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environmental quality. For example, the flow of sediment filtration services can be estimated by
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calculating the difference between ambient sediment concentrations (e.g. total suspended solids)
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and cumulative sediment loading throughout the watershed. Likewise, the flow of carbon
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sequestration should be measured as the amount of carbon taken up and stored in vegetation,
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rather than the amount of atmospheric carbon. Ecological work provides a measure of RS flow
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that cannot be deduced from environmental quality measures alone. Ecological pressures, like
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sediment loading, can be quantified in several ways, including direct field monitoring or
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estimated by widely accepted models, like the Revised Universal Soil Loss Equation (RUSLE)
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or Soil and Water Assessment Tool (Sahu and Gu, 2009). Since absolute values may not exist for
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all ecological pressures or for environmental quality in all areas, relative measures can be used.
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Where neither relative measures nor appropriate models exist, expert judgment is an alternative
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(MA, 2005; Burkhard et al., 2012; Nedkov and Burkhard, 2012). The analytical goal is to
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incorporate spatiotemporal variability in ecological pressures to better evaluate RS flow. By
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evaluating ecological pressures in conjunction with environmental quality, we get a more reliable
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estimate of RS flow which can be compared to estimates of capacity to assess the state of the
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ecosystem, the condition of the service, and sustainability of current land practices.
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Our approach to estimating RS flow is designed to provide information to avoid
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ecological degradation, but may also be helpful in developing mitigation strategies to reduce
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existing degradation. Once areas of high ecological pressure and low capacity are known,
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degradation can be avoided by reducing pressures, increasing capacity (e.g. via restoration or
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best management practices), or enhancing the capacity of other services that influence pressures.
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Identifying which ecosystem properties and processes contribute to RS capacity and which land
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use practices influence ecological pressure (Fig. 2) can help managers develop strategies to plan
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for or mitigate changes in environmental quality.
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5. Conclusions
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Our approach to assessing ES, using separate measurements of ES capacity, pressure,
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demand, and flow, is useful and innovative in that it quantifies the components of ES delivery
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rather than merely measuring final services or environmental quality. By so doing, we can more
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accurately characterize service delivery, sustainability, and ES trade-offs across space and
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through time. Using information about all four aspects of ES, planners can more effectively
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evaluate whether the needs of people can be met sustainably (i.e. without degradation) by
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existing capacity or if alternative measures are needed (e.g. restoration or technological
384
substitutes). This multi-component ES approach also enables scientists to assess regulating
385
services more accurately by measuring RS flow as the regulation of ecological pressures, rather
386
than measures of environmental quality. Measuring the actual flow of services provides a metric
387
for assessing ES equity, while capacity measures inform decisions about future development and
388
management. Collectively, our multi-component framework offers a more comprehensive
389
assessment of ES delivery, sustainability, and the trade-offs associated with land use. Our
390
approach also accounts for temporal variability in all components of ES provision, especially
391
ecological pressures and societal demand, which are likely to change through time.
392
To facilitate widespread use of ES knowledge in environmental management and
393
conservation planning, we need a more flexible, coherent, and informative framework that
394
accounts for spatiotemporal differences in how ES are produced and delivered (de Groot et al.,
395
2010; Chan et al., 2012). This framework should distinguish between potential service
396
production and the flow of services and be applicable across a wide range of ecosystems and
397
services (de Groot et al., 2010; Tallis et al., 2012). Our approach for analyzing ES represents
398
significant steps toward meeting these needs as this ES framework can be applied at virtually any
399
spatial resolution or extent for which ES components are measured separately. Furthermore, the
400
framework can be easily incorporated into scenario analyses (MA, 2005; Troy and Wilson, 2006)
401
to produce more objective and accurate assessments of service capacity, ecological pressure,
19
402
expected demand, and service flow which can better guide land management decisions (van
403
Oudenhoven et al., 2012).
404
405
406
Acknowledgments
407
408
This work was funded by the U.S. Geological Survey’s National Aquatic Gap Analysis
409
Program. We thank D. Beard, C. Beier, E. Frimpong, K. Limburg, B. Mogollon and anonymous
410
reviewers for their valuable input and feedback throughout the development of this and related
411
studies. The Virginia Cooperative Fish and Wildlife Research Unit is jointly sponsored by the
412
U.S. Geological Survey, Virginia Polytechnic Institute and State University, Virginia
413
Department of Game and Inland Fisheries, and Wildlife Management Institute. Use of trade
414
names or commercial products does not imply endorsement by the U.S. government.
415
416
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Table 1
Components of ES
Delivery
ECOSYSTEM SERVICE CATEGORIES
Provisioning
Regulating
Cultural
ECOSYSTEM
Biophysical
Biophysical
Biophysical and social
SERVICE CAPACITY:
capacity; feature-
capacity;
capacity; feature- and
An ecosystem’s potential
based
process-based
process-based
to deliver services based
(e.g. modeled water
(e.g. modeled
(e.g. model potential
on biophysical and social
supply)
carbon
to provide experience)
properties and functions1
sequestration)
ECOLOGICAL
Events that reduce
Environmental
Events that reduce
PRESSURES:
stock and/or
disturbances that
stock, regenerative, or
Anthropogenic and
regenerative
increase the amount
assimilative capacity
natural stressors that
capacity (e.g.
of ecological work
of a system;
affect capacity or flow of
overharvest; water
required to meet
commonly related to
benefits; often attributed
impoundments)
societal demands
overuse
to overuse or feedback
(e.g. pollution,
(e.g. soil compaction,
from land management
impervious
erosion)
decision to enhance other
surfaces)
service capacities2
ECOSYSTEM
Amount of service
Amount of
Desired total use (if
SERVICE DEMAND:
desired per unit
regulation needed
rival service) or
The amount of a service
space and time
to meet pre-
individual use (if non-
required or desired by
multiplied by the
determined
rival)
27
society3
number of potential
condition
(e.g. total visitor-days
users (rival service)
(e.g. % nitrogen
from year prior;
(e.g. liters of water
reduction; TMDL)
individual visitation
per person)
rates)
ECOSYSTEM
Quantity harvested,
Ecological work =
SERVICE FLOW: The
consumed, or used;
ecological pressures used measured in
actual production or use
number of people
minus
units of time and/or
of the service;
served; number of
environmental
space
incorporates biophysical
industries served
quality (same units)
(e.g. total visitor-days
and beneficiary
(e.g. nitrogen
from current year;
components4
inputs-in-stream
individual visitation
load)
rates)
1
Amount of service
Cairns (1997); Chan et al. (2006); (2011); Egoh et al. (2008); Daily et al. (2009); van
Oudenhoven et al. (2012). 2Beier et al. (2008); Rounsevell et al. (2010); van Oudenhoven et al.
(2012). 3McDonald (2009); Nedkov and Burkhard( 2012). 4Beier et al. (2008); Layke (2009); de
Groot et al. (2010); Oudenhoven et al. (2012).
552
28
553
554
Table captions
555
Table 1: Ecosystem service delivery process comprises four distinct components which differ
556
among three ecosystem service categories. A general definition and examples are provided for
557
each category-component combination.
558
Figure captions.
559
Fig. 1: The main components of the ecosystem service delivery process (boxes) are
560
interconnected such that a change in one affects the others (arrows). A wide array of terms has
561
been used interchangeably throughout the literature. For each main component (box), we cite
562
authors who have adopted that term and provide alternative terminology cited in the literature.
563
Ecological pressures (pink box) have a direct effect on the capacity of an ecosystem to provide a
564
service and can affect the flow of the services (black box). Likewise, societal demand (red box)
565
can influence ecological pressures and the flow of services from ecosystems to beneficiaries
566
(purple box) and the needs and preferences of beneficiaries influence societal demand.
567
Fig. 2: Conceptual models illustrating the effects of land use (middle) and human population
568
(right) changes on regulating service (RS) capacity, ecological pressures, societal demand for
569
regulating services, and the flow of services in a watershed in which upstream areas are largely
570
forested e.g. 80-year rotation timber production) and downstream areas are predominantly
571
agricultural and rural-suburban development left). The middle panel illustrates how a clear-cut,
572
for coal extraction or a housing development, in the upper forested area would decrease the
573
landscape’s water retention capacity, which would increase runoff and ecological pressure on
574
flood regulation downstream. Similarly, the loss of forested cover would likely decrease the
575
sediment retention capacity upstream, thereby increasing ecological pressure on sediment
29
576
regulation in the lower basin. In this case, service flow increases because of the additional work
577
the ecosystem must perform to maintain desired environmental quality. Service flow can also
578
increase because of additional beneficiaries. The right panel illustrates how an increase in human
579
population density downstream would increase the societal demand for the regulating service.
580
Increases in ecological pressure or societal demand will increase service flow, given that the
581
system has sufficient capacity to produce the service.
582
Fig. 3: Conceptual model illustrating water quality regulation. the movement of water across the
583
landscape (surface and subsurface), and the major components of the ecosystem service delivery
584
process, including capacity (green boxes), ecological pressures (pink ovals), demand (red
585
arrows), and service flow (black arrows). Beneficiaries (purple ovals) are shown as the source of
586
demand and the recipients of regulating service flow. As water is introduced to the ecosystem, by
587
means of precipitation or upland flow, a series of processes can act to regulate water quality.
588
High capacity of horizontal and vertical retention reduces the ecological pressures on surface
589
filtration and deposition.
590
Fig. 4: The flow of ecosystem services (ES) can vary greatly depending on area of service
591
production, its natural flow paths, as well as anthropogenic flow corridors. For many freshwater-
592
related services the flow path is naturally hydrologic where the capacity to produce a service
593
upstream affects the flow of benefits downstream top). Alternatively, the benefit zone can be
594
extended by anthropogenic corridors like roads, canals, or exportation bottom).
595
Fig. 5: Differences in service delivery and the effects of ecological pressure on environmental
596
quality and ecological work within ecosystems with little to no capacity A) compared to that of a
597
system with high regulating capacity B). Environmental quality is a function of regulating
30
598
capacity and ecological pressure. In systems with little to no capacity A), environmental quality
599
is quickly degraded in response to increasing ecological pressure. Systems with higher capacity
600
can maintain better environmental quality under greater ecological pressure B). Ecological
601
thresholds are determined by the ecosystem’s capacity to provide a service. Once this threshold
602
of ecological pressure is exceeded, environmental quality will degrade. The shaded polygon B)
603
illustrates the amount of ecological work performed i.e. regulating service flow), which
604
represents the difference between environmental quality and ecological pressure.
31