Economic valuation of ecosystem services in a mangrove setting
Miranka van Breugel Supervisors: Tjeerd J. Bouma, Jim van Belzen
s1965166 Date: 05/08/2015 Length: 4,691 words Total word count: 7,280
Abstract
Economic valuation of ecosystem services (ESS) has been suggested as a solution to the problem of underrepresentation of ecosystem values in policy decisions worldwide. The production functioning, household production function, stated preference and replacement cost/
cost of treatment methods (all operating from an anthropocentric approach) may translate ESS values into economic values. The emergy method is suggested as an alternative valuation method, using a biocentric approach to value ecosystems based on energy and/or material flow, rather than economically. Valuation methods may be used to increase tropical wetland protection, which is desperately needed due to their systematic degradation across the globe.
As an example of how this may be achieved, a valuation of mangroves is included, showing the relative human need for their ESS and providing examples of their economic valuation.
Economic valuation of ecosystem services in a mangrove setting
Introduction 3
I. Ecosystem services valuation 3
ANTHROPOCENTRICAPPROACH 4
ECONOMICVALUATIONMETHODS 4
1. Production functioning methods 4
2. Household production function methods 5
3. Stated preference methods 6
4. Replacement cost or cost of treatment methods 6
DISCUSSION 6
PROSPECTS 7
II. Tropical coastal wetlands 7
MANGROVES 8
1. Goods 8
2. Services 9
Conclusions 10
Bibliography 11
Introduction
Due to technological advances and man-made alternatives, the products that nature offers us are often undervalued (Bobylev, 2010; NRC, 2004). However, public awareness is on the rise. Environmental change, as well as resource depletion (e.g., our declining fish stocks) are forcing global politics to find alternatives and embrace the importance of natural conservation. The difficulty lies in the human tendency to define value economically. Science and policy is now faced with some important questions that need answering. How do we define the services that a healthy natural system has to offer humanity?
How can we value those services in terms of our monetary system? An extensive literature study has provided some answers, which will be discussed in chapter I. Chapter II zooms in on the ESS provided by mangroves and their economic value. Tropical coastal wetlands are being degraded and destroyed at an alarming rate, in pursuit of what seems to be economic profit (Barbier et al., 2011). The products and life support functions these ecosystems provide are disappearing along with them, posing the following question: can man-made alternatives outcompete the economic value of healthy tropical coastal wetlands? Finally, the livelihoods of many coastal populations are dependent on tropical coastal wetlands (Sandilyan & Kathiresan, 2014). How will these people be affected when coastal systems disappear, or when they are preserved or reconstructed?
I. Ecosystem services valuation
Throughout history human civilization has been dependent on marketable goods and a variety of life support functions that nature has to offer
(Hernández-Morcillo, 2013). These provisions are termed ecosystem services (ESS) and are a direct result of a healthy natural environment (NRC, 2004). A recent study estimated the total value of global ESS at as much as US$
149.61 trillion, 75.5% of which is provided by marine systems (Li & Fang, 2014). What sets ESS apart from other natural services, is that there is a human demand for them (Liotta et al., 2010). This paper will focus on the services provided by coastal ecosystems in the tropics. In spite of their importance, the values of these services are rarely adequately represented in policy decisions (Zhao & Wu, 2015). Economic growth remains the goal and the economic value of ESS has often been indirectly placed at zero (NRC, 2004). As a r e s u l t , m a n y e c o s y s t e m s h a v e b e e n degraded, polluted or removed altogether, buckling under the effects of human impact (Zhao & Wu, 2015; Halpern et al., 2008).
Human development has generally focussed on improvement of infrastructure, seemingly rendering ESS obsolete (Bobylev, 2010; see Table 1). However, research indicates that the conservation of natural ecosystems may be economically preferable over continuation of habitat conversion for human needs (Balmford et al., 2002). Furthermore, people in developing areas, particularly those living
Service to human welfare Rural areas developed countries
Urban areas developing countries
Urban areas developed countries
Clean air to breathe E E E
Comfortable climate conditions E E E
Water level in water bodies (for shipping, amenity, biota)
E E E I
Groundwater level E E I E I
Water quality to use as amenity and recreation
E E E
Drinking water provision I I I
Soil formation E I E I
Waste decomposition E E I I
Biological populations control E E I I
Habitat E E I I
Food I I I
Raw materials E I I
Recreation and outdoor activities E E I E I
Table 1. Provisioning Services to Human Welfare in Different Settings (minor service providers are excluded) - Service provided by E—
Ecosystems; I—Infrastructure. Source: Bobylev, 2010.
below the poverty line, are most dependent on ecosystems (McKenzie, 2011; Bobylev, 2010, see Table 1). It is argued, that by placing an economic value on coastal ESS, their value can be kept into account in regular cost-benefit analyses, which are common for policy decisions (McKenzie et al., 2011). If so, the value of coastal ecosystems could be incorporated in global decision-making, which may help conservation efforts as well as human wellbeing and even poverty alleviation (McKenzie et al., 2011;
Ewel, 2010).
ANTHROPOCENTRICAPPROACH
Providing valuation of ESS in an economic context may help their consideration in policy decisions (McKenzie et al., 2011). This requires a clear and consistent definition of ESS and a wider understanding of their key characteristics (Fisher et al., 2009). Goulder & Kennedy (2011) describe the anthropocentric (human oriented) and biocentric (nature oriented) approach as two different viewpoints from which value may be attributed to an ecosystem. In the anthropocentric approach, something is only deemed to have value in such a way that humans can draw satisfaction from them. The benefit of an ecosystem to other living beings is only valued in the sense that their wellbeing indirectly influences human wellbeing. Since ESS are valued by their usefulness to humans, the anthropocentric approach is preferred in economic valuation (Liotta et al., 2010). The Millennium Ecosystem Assessment of 2003 (p. 53) even defines ESS as 'the benefits people obtain from ecosystems'.
The biocentric approach places value upon ecosystems for how they benefit humans as well as other living beings directly, even if the benefit to other beings does not influence human wellbeing (Goulder &
Kennedy, 2011). This approach may also be referred to a as the intrinsic value approach. In spite of its more complete understanding of ecosystem values for the Earth as a whole, this method is generally not used in economic assessments.
Anthropocentric values may be categorized in consumptive and non-consumptive values (Barbier, 2011). A healthy wetland ecosystem may be of consumptive value in that it supplies edible fish. A non- consumptive value may be its flood management capability. A further categorization in use and non-use values can be made (Barbier, 2011). Consumptive values are always considered use-values. Non- consumptive values such as flood management are also use-values. Non-use values may be placed on an environment by individuals that simply value the knowledge that a certain area exists, even though they may never visit it. These are always non-consumptive values.
Anthropocentric values may be expressed in a willingness to accept (e.g., how much financial compensation is needed for a person to accept loss of an ecosystem service) and willingness to pay (e.g., how much money a person is willing to pay to protect an ecosystem service) (NRC, 2004). These expressions of ecosystem service value provide the basis of several different valuation methods.
ECONOMICVALUATIONMETHODS
In order to value anthropocentric benefits economically, the literature has described several different methods. The NRC (2004) describes (1) production functioning methods (consumptive use values), (2) household production function methods ((non-)consumptive use values), (3) stated preference methods (may be based on (non-)consumptive (non-)use values) and (4) replacement cost or cost of treatment methods (may be based on (non-)consumptive use values) (see Table 2).
1. Production functioning methods
Production functioning methods help place an economic value upon several ecosystem functions which can increase production of a marketable good (NRC, 2004). The increase in production, resulting from a better functioning ecosystem, can be economically valued, indicating the ecosystem service’s value. For example, when an aquatic ecosystem becomes healthier, fish stock may increase, decreasing the costs of catch (Robertson & Duke, 1987; NRC, 2004). The decrease in catch costs may increase profit and translate into the economic value of the improvement of the aquatic ecosystem. As an example, this method has been used in the UK to determine the marginal value of pollination services (Breeze et al., 2015).
2. Household production function methods
Household production function methods focus upon the uses and values households may have for ecosystem services (NRC, 2004). These are often related to recreation, purity of resources and property values. Recreational values are determined by random utility and travel-cost models (RUM). These are based upon the expenses individuals are willing to make (willingness to pay) in order to make use of a specific ecosystem. This includes traveling costs to the location and potential profit from activities such as fishing for own consumption. Application of this method is most suitable when measuring income from recreation and tourism (Barbier, 2007). A Greek case study used the travel-cost method to estimate the decrease in tourist demand for outdoor recreational services, as the result of the economic crisis, for a protected riparian ecosystem (Latinopoulos, 2014). In this case study, the economic crisis indirectly lead to a decrease in the recreational value of the studied ecosystem. Surveys were used to inquire visitors about things such as the number of day-trips taken by each individual over a designated time period, as well as their travel costs, time spent at the site and mode of transport. In Penghu, Taiwan, this non-market method has also been used to determine the recreational value of an artificial reef, which was initially established to enhance fish stocks (Chuang et al., 2013). The travel-cost method has even been suggested as an ecosystem valuation tool in oil spill impact assessment (Depellegrin & Blazauskas, 2013).
Values placed upon purity of resources may be determined with averting behavior models (NRC, 2004). These are best applicable when determining the health effects arising from pollution of a site (Barbier, 2007). For example, a polluted water source may force a family to purchase a filtering system or to buy bottled water from the supermarket (NRC, 2004). The extra costs made by avoiding the polluted resource indicate the value a household places upon unpolluted resources.
Hedonic methods use property values as an indication of certain ecosystem service values. Property values are often based upon esthetics and cleanliness of the surroundings. The difference in price between two similar properties, one nearing, for example, a lake and the other not, indirectly indicates the value placed upon such an ecosystem. Furthermore, a property bordering a polluted lake is likely to increase in value if the lake were to become pollution-free. This increase in price gives an economic valuation of the ecosystem’s cleanliness. As an example, hedonistic valuation methods were applied in Vienna to estimate the value of its greenbelt (Herath et al., 2015). Results indicated that property value was negatively correlated to distance from the greenbelt. Thus, hedonistic methods provide implicit ecosystem values, since they are not attributed to the resource directly, but rather to a property nearing it (NRC, 2004).
Econ. Valuation Methods
models used ESS measured Marketable
ESS?
1. Production functioning
Production increase Yes
2. Household production function
-
RUM-
Travel-cost-
Averting behavior-
HedonicRecreation, pollution relief, property value increase
Indirectly
3. Stated preference
-
continuent valuation-
conjoint analysisEsthetics, emotional value No
4. Replacement cost / cost treatment
Infrastructure-like services Indirectly
Table 2. Overview of all mentioned economic valuation methods, indicating for which ESS they may be applicable and whether or not these services are marketable. Based on methods as described by NCR, 2004.
3. Stated preference methods
Stated preference methods are used to acquire the economic value of non-marketable ecosystem services (NRC, 2004). Questionnaires paint an image of how much economic value individuals place on them. This method knows two different types: contingent valuation and conjoint analysis. With contingent valuation, an economical value is placed upon the environment directly. Respondents are provided with a written or verbal description of the environment in question. They are then asked how much money they would pay (willingness to pay) for the environment not to undergo a negative change. This method has been used in the UK, as an addition to valuation through the production function method, to determine willingness to pay to halt the decline in pollination services (Breeze et al., 2015). It has also been used to estimate the multi-functionalities value of man-made wetlands in the form of paddy rice fields in Korea, which was estimated to be higher than the economic value of the country’s rice production itself (Yoon, 2009). Without proper valuation methods, this benefit would probably have been overlooked.
Conjoint analysis is a much newer method, which makes a distinction in key aspects that an environment has to offer (NRC, 2004). Respondents are often provided with different alternative situations (e.g., three marsh restoration projects) and asked to state their preferred alternative or to rank the options. The economic value of these procedures is then used to indirectly determine the economic value of the ecosystem. Recently, a Japanese case study used this method to determine willingness to pay for ecosystem services of open oceans (Shen et al., 2015).
4. Replacement cost or cost of treatment methods
If the above mentioned methods are insufficient in describing the economic value of an ecosystem service, researches have sometimes resorted to replacement cost or cost of treatment methods (NRC, 2004; Barbier, 2011). The first method estimates how much the least costly available alternative to an ecosystem service would cost. For example, if a coast wetland provides purified ground water, the costs of the least expensive water purifying installation may indicate the replacement costs of this ecosystem service. This method is often used in combination with one or more of the above stated methods and is highly applicable to the services provided by coastal wetlands, such as climate regulation, water supply, flood control, environmental purification and nutrient conservation, which are often marketable by comparison to man-made alternatives (Li et al., 2015; Madani et al., 2014; Grossmann, 2012).
The cost of treatment method is better used in situations of imminent threat. For example, if a critical level of pollution is about to be reached in a natural environment. Both these methods have a tendency to overestimate the value of the provided service (NRC, 2004). However, they may provide a last resort valuation method if the provided alternative provides the same services, the least-cost alternative is used for comparison and if there is enough evidence to support that the service would be demanded by society if it were provided by that least-cost alternative (Shabman & Batie 1978).
DISCUSSION
Stated or shown preference are based upon the way in which individuals value ecosystems and their services (NRC, 2004). However, people are often not fully informed about an ecosystem’s benefits, or the costs of its loss. The opinions and actions of well-informed and environmentally involved respondents are valued the same as uninformed or uninterested respondents. This may negatively affect the valuation methods and provide an under- or overestimation of the true value of a system to humanity as a whole.
Attributing more value to the opinions of informed individuals may provide a more accurate estimation of economic value. However, this distinction is quite difficult to make and not easily integrated in policy measures. Furthermore, the degree on which an individual is informed may vary, further complicating the process. Literature often does not prefer replacement cost or cost of treatment methods and advices its use only as a last resort (NRC, 2004). However, they may provide a good addition to stated and shown preference methods. Loss of a certain function will require replacement on the long run, which should be accounted for in policy making. Combining the replacement cost or cost of treatment approach with stated and shown preference methods, may provide a complete picture of esthetic, recreational and practical value of an ecosystem and its services. Production functioning methods may then provide a final
interpretation of the market value benefits an ecosystem may provide. Generally, it seems important to involve all of the above stated methods in the ecosystem valuation process. Each key aspect of the ecosystem needs its own applicable approach, in order to provide a proper economic valuation of the ecosystem as a whole.
PROSPECTS
Standardization of economic values is needed, to allow for trade-off calculations and comparison between studies (Pernetta et al., 2013). This may be achieved by transforming local currencies into US$ and converting these values to a standard year (2007) by means of the consumer price index (Pernetta et al., 2013). It is argued that the definition of ESS themselves may also need standardization, to ensure their comparability with conventional goods and services found in GDP and other national accounts (Boyd &
Banzhaf, 2007). By integrating direct ecosystem services into GDP, green GDP may be determined, providing an effective economic indicator of environmental management (Linyu et al., 2010).
In a recent article, Zhao and Wu (2015) go against these types of valuation, arguing that they only consider direct uses and products and fail to recognize other valuable aspects of ecosystems. They suggest using the emergy synthesis method instead, providing a biocentric valuation of goods and services based on all the inputs and outputs that support a system (Zhao & Wu, 2015). Thus, this method takes ecosystem valuation to the next level, stepping out of the perception that only ESS should be valued, and takes on a biocentric approach, rather than an anthropocentric one (Goulder & Kennedy, 2011). The emergy method also by-passes the need for economic valuation, since it uses energy and/or material flow (specifically organic matter production, raw materials, habitat, disturbance regulation, waste treatment and scientific research, in the case of mangrove valuation) as the common denominator (Zhao
& Wu, 2015; Odum & Odum, 2000). This technique has, e.g., been used to determine an ecosystem’s contribution to wood species formation, affecting the production of wood biomass (organic matter) (Neri et al., 2014).
Valuation of ecosystem services always has to deal with certain uncertainty, since their future value may be different from that at the moment of evaluation (Barbier, 2007). For example, it is likely that, as ecosystems continue to be degraded, their provided services will become rarer and thus relatively more valuable. As technology keeps advancing we may also find added uses for ecosystem services, further increasing their potential value. More empirical research into this aspect of ESS valuation will be needed, to make the results of estimations more reliable.
II. Tropical coastal wetlands
Around tropical latitudes, five types of coastal wetlands can be found: coral reefs, sea grass beds, mangroves, salt marshes and sandy beaches and dunes (Barbier, 2011). Considering their broad array of ecosystem services, coral reefs, sea grass beds and mangroves are among the most valuable wetlands the earth has to offer (Aber et al., 2012). Unfortunately, they are also some of the most heavily used and threatened natural systems worldwide: it is estimated that around 35% of mangroves, 30% of coral reefs and 29% of sea grass beds are either lost or degraded (Barbier, 2011). Unless the value of ESS to local coastal communities is estimates, it will be difficult to convince policymakers to consider alternative land use policies (Barbier, 2007). The loss of one type of system may have big consequences for the remaining ones, since the three types of tropical coastal wetlands are interconnected, forming a single
“seascape” (Barbier, 2011). For example, mangroves may export nutrients to sea grass beds off shore (Walton et al., 2014). In return, detritus from sea grass beds flows back into the mangrove systems, creating a circular balance in nutrients. Connectivity between mangroves, sea grass beds and coral reefs may also enhance the productivity of important fishery stocks by providing a nursery for juveniles (Nagelkerken et al., 2015; Paillon et al., 2014). While adults generally collect in more off-shore habitats (seagrass beds and coral reefs), juveniles are more abundant near-shore (mangroves and seagrass beds), indicating the importance of mangroves as a nursery for off-shore species (Ramos et al., 2015).
Within this network of habitats, each type of wetland has its’ own functions and services. The literature describes three different categories under which ecosystem services can be classified economically
(Barbier, 2007): (1) goods, (2) services and (3) cultural benefits. In the case of wetlands services may be further narrowed down into coastal protection, water purification and important habitat for offshore fisheries (Barbier, 2011). Many ESS provided by sea grass beds and coral reefs, such as coastal protection and fish production, are also provided by mangroves. Mangroves also provide extra benefits such as wood production and due to their attachment to the coast, they are most easily accessible to humans and most threatened. Therefore, this chapter will focus on mangrove ESS, as an example for ESS valuation for tropical coastal wetlands, providing scientific evidence for their usefulness. Several case studies will then be provided to illustrate common economic valuation practice for mangrove ecosystems.
MANGROVES
The iconic vegetation type within mangrove habitats are mangrove trees. Three types of mangrove trees are generally described (Taketani et al., 2011). Red mangroves, such as the Rhizophora species, occupy the sea-ward edge of a mangrove forest (Kathiresan & Bingham, 2001). Their tangled roots extend from the trunk, as well as the branches (FDEP, 2015). Black mangroves, such as the Avicennia species, occupy land further away from the sea (Kathiresan & Bingham, 2001). They have iconic aerial roots which stick up above ground and allow them to live in oxygen deprived soil (Taketani et al., 2011). White mangroves, such as the Laguncularia species, occupy the highest elevations and show neither tangled roots nor aerial roots (FDEP, 2015). Mangroves are highly tolerant to saline conditions and can change their structure at the root, leaf and stand level to regulate water loss (Reef & Lovelock, 2015). They provide a large number of ecosystem services, which may be valued economically (Mukherjee et al., 2014). The development of restoration and rehabilitation methods is un-going and restored mangroves are seemingly successful in achieving ecosystem recovery (Field, 1998; Bosire et al., 2008). Well-funded economic valuation is becoming increasingly important, since it may help decision makers appreciate the value of provided ESS and increase the incentive to restore, rehabilitate or conserve mangrove ecosystems (Mukherjee et al., 2011).
1. Goods
As a coastal forest, mangroves provide local communities with a supply of wood (Feka et al., 2015).
Fuelwood from mangroves may sustain domestic uses, such as cooking and heating, in the Pacific and in Asia (Knox & Miyabara, 1984). In 1998, up to 90% of the fuel used in Vietnam could be traced back to mangroves, either from using the wood directly or by producing charcoal first (Bandaranayake, 1998).
Furthermore, species- and size-selective harvest may provide wood for construction (Walters, 2005).
Another local use of mangroves is the extraction of chemicals for the production of folkloric medicine (Bandaranayake, 1998). For example, a compound called triterpenoid saponin may be extracted from Avicennia marina, a black mangrove species (Bandaranayake, 1998). Although less effective than morphine, it provides significant pain relief (Padmakumar et al., 1993).
Sea-food, a better known mangrove resource, also benefits from a healthy mangrove ecosystem. Their under water root systems provide shelter to marine fauna, such as prawns, crabs and fishes (Nagelkerken et al., 2008). By providing a habitat to these important species, mangroves prove to be an important source of sea-food, which can be either consumed or sold, for coastal communities (Béné et al., 2011; McClanahan et al., 2015). In fact, fisheries supported by mangroves are estimated at an annual market value of US$ 750 to 16 750 per hectare (Rönnbäck, 1999).
2. Services
T h e t o p t h r e e m o s t economically valuable ESS provided by mangroves are (1) fisheries, (2) coastal protection a n d ( 3 ) p r o t e c t i o n f r o m sedimentation, in that order (Mukherjee et al., 2014; see Fig 1). Pollution abatement can also be found in their list of e c o n o m i c a l l y i m p o r t a n t services. Literature reviews, backed up by several case studies, may provide a clear definition of these services and estimates of their economic value.
Fisheries & Aquaculture
Mangroves have been proven t o p r o v i d e a n u r s e r y f o r
commercially exploited fisheries in South-East Asia (Robertson & Duke, 1987). They provide shelter and food to juvenile reef fishes and are known to sustain biodiversity in the Western Atlantic and South Pacific (Paillon et al., 2014). Unfortunately, mangroves are being transformed into salt water shrimp farms at an alarming rate (Primavera, 1997; Tenório et al., 2015). A Brazilian case study states that the revenue received from shrimp farming would be lower than the costs of mangrove degradation, based on value assignments by Aburto-Oropeza et al. (2008) and Barbier et al., who estimated the mean global value for mangroves at approximately US$ 37,500/ha/year and US$ 16,100/ha/year respectively (Tenório et al., 2015). However, local people may find it difficult to understand the value of mangroves when no direct income is generated, allowing shrimp farming to sound more profitable than maintaining natural ecosystem services (Kuenzer & Tuan, 2013).
Coastal protection
Estuarine ecosystems are reportedly indispensable in their protection of terrestrial ecosystems, being the first in line of defense against hazards of oceanic origin (Ghorai & Sen, 2015). Healthy mangroves can significantly decrease wave action caused by extreme weather, and prevent soil erosion (Cuc et al., 2015). This may become increasingly important as research predicts that extreme weather events may increase in strength as sea-water temperatures continue to rise (Satheeshkumar et al., 2010). Several case studies around the Indian Ocean, an area that is rich in mangroves, indicate that presence of a thicker mangrove forest results in less tsunami damage to coastal villages (Danielsen et al., 2005;
Kathiresan & Rajendra, 2005). A post-tsunami case study into Sri Lankan mangrove sites, suggests this as well (Dahdouh-Guebas, 2005). Some argue that coastal protection by mangroves is questionable, since reanalysis of the same data from Indian Ocean sites, found no significant relationship between human mortality and the extent of mangrove forest fronting coastal hamlets (Satheeshkumar et al., 2012;
Kerr et al., 2006; Baird et al., 2009). It is argued that empirical studies on mangroves’ protection service use small samples and inadequately control for cofounding factors (Das & Vincent, 2009). Such cofounding factors include distance to the shore and elevation above mean sea-level, which also influence mortality and property loss as a consequence of a tsunami, making it difficult to define the mangrove’s effect after a tsunami has occurred (Vermaat & Thampanya, 2006; Vermaat & Thampanya, 2007). Although observational studies have not provided conclusive results, several numerical and physical models suggest protection capabilities of mangroves against cyclone storm surges and small tsunamis (Marois & Mitsch, 2015). They may also protect villages against damage caused by cyclonic
Fig 1. Ranking of the ecosystem service categories of mangroves resulting from the scores given by 106 mangrove experts (scientist, reserve managers and field-based conservationists). Source: Mukherjee et al., 2014).
winds (Das & Crépin, 2013). The ability to absorb wave and wind energy strongly depends on aspects such as tree density, which is dependent on the conservation of the mangrove forest (Alongi, 2008).
Therefore, their conservation is of high importance and considered economically justified (Das & Vincent, 2009; Sandilyan & Kathiresan, 2015).
Pollution sequestration
The root systems of mangroves decrease the flowing speed of the surrounding water, increasing soil accretion and resulting in elevation change (Krauss et al., 2014). Some models suggest that soil accretion rates could keep up with predicted sea-level rise, further increasing coastal protection against climate change (Parkinson et al., 1994; Alongi, 2008, Krauss et al., 2014). Mangroves also provide carbon sequestration, an important regulatory service with the potential to mitigate global warming (Zarate- Barrera & Maldonado, 2015). A Brazilian case study estimated the economic value of carbon sequestration by mangroves as varying from $US 19.00 +- 10.00 per hectare per year (for basin forests and high intertidal) to $US 82.28 +- 32.10 per hectare per year (for fringe forests and low intertidal) (Estrada et al., 2015). This potential decreases as mangroves are degraded, providing further incentive for mangrove conservation (Hemati et al., 2015).
Mangroves also provide a buffer zone between anthropologically polluted areas and the sea (Saenger et al., 1990). Along with soil accretion, pollutants such as heavy metals tend to settle (Lewis et al., 2011).
These may then be taken up by the mangroves, which play an important role in sequestering metals from the sediment and water column (Nath et al., 2014). When mangroves are diminished these accumulated pollutants are released to the environment, causing heavy metal contamination in nearby sea-grass beds, coral reefs and coastal people (Sandilyan & Kathiresan, 2014).
Conclusions
Increased human development (HDI) is generally accompanied by a shift from being dependent on natural systems towards being dependent on infrastructure, for services such as water supply and waste removal (Bobylev, 2010). Infrastructure, however, is often costly to build and maintain and may damage or destroy ecosystems and their services. Several studies indicate that it is economically beneficial to maintain natural mangrove ecosystems, over continuing to convert them (Vincent, 2009; Das & Sandilyan
& Kathiresan, 2015; Tenório et al., 2015). Furthermore, the mere action of removal may release heavy metals and other pollutants in the environment, causing direct economical problems (Saenger et al., 1990; Lewis et al., 2011; Nath et al., 2014; Sandilyan & Kathiresan, 2015). Most of the effect from maintaining or removing mangroves are experienced by coastal populations, especially those with less developed infrastructures (Bobylev, 2010; Ewel, 2010; Liotta, 2010, McKenzie et al., 2011). Due to the fact that developing communities, especially those living below the poverty line, are more dependent on ESS, proper management of these natural riches has the potential to increase their livelihoods and alleviate poverty (NRC, 2004; Barbier, 2007; see Table 1). For instance, they provide local communities with fire wood, construction material, food and even pharmaceuticals (Knox & Miyabara, 1984;
Bandaranayake, 1998; Walters, 2005; Feka et al., 2015). A case study in Can Gio, Vietnam indicates that local people often find it difficult to understand the value of mangroves when no direct income is generated (Kuenzer & Tuan, 2013). However, household surveys in the same area show a clear appreciation and understanding of their importance. Inquiries using the stated preference method, showed a clear preference for maintaining natural ecosystem services, in spite of potential economic gains of aquaculture development (McDonough et al., 2014). It is argued that economic valuation of ESS will help convince policymakers of wetland importance as well, and might help them refrain from coastal development (Barbier, 2007). A combination of the mentioned methods is currently the best guess for incorporating all aspects of ESS. New, more encompassing methods for economic valuation continue to add to available tools (Goulder & Kennedy, 2011; Zhao & Wu, 2015). Standardization of values and ESS units will help create homology within evaluation research and aid in the comparison with other economic activities (Pernetta et al., 2013; Boyd & Banzhaff, 2007). Furthermore, proper valuation of ecosystem
services may aid in environmental, food and human security, as well as improvement in quality of life (Bobylev, 2010; Alpas & Kiymaz, 2010).
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