Economic Valuation of Ecosystem Services by Using the Analytic Hierarchy Process and the Analytic Network Process. Comparative Analysis Between Both Methods in the Albufera Natural Park of València (Spain)

2.1 The Albufera Natural Park

The Albufera Natural Park of Valencia (the third biggest city in Spain) is placed in the Mediterranean coast line about 7.5 kilometers south of the Turia river mouth. Nowadays, the Natural Park has an approximate surface area of 211.2 km², although the freshwater lagoon is about 23.94 km². Most of the surface is taken up by fields with rice crops and marshlands.

This area was declared as a Natural Park in 1986 and afterwards it was included among the ‘International Important Wetlands record’ established by the Ramsar agreement [7].

This Natural Park is one of the most significant wetlands in Europe and a population of up to one million inhabitants surrounds it. Despite its ecological and economic value, there have been several negative environmental impacts related to the water quality or the biodiversity loss since the 80s, which have been produced by the ongoing lake’s eutrophication or the progressive devaluation of the forest area.

Apart from the crops, other economic activities can be found in this area such as hunting and fishing, even though both have been reduced during the last decades. In addition, some spaces of the Albufera Natural Park are receiving many tourists due to the aesthetic, landscape and recreational value of the area.

Finally, it is necessary to consider the cultural services such as paintings, literature or religious festivals. For instance, painters such as Joaquín Sorolla or writers such as Vicente Blasco Ibáñez have been inspired by this place as many people are due to the identity value of the area. Moreover, the Latin sailing and the traditional fishing which have been both declared as a Good of Cultural Interest by the Valencian Regional Government in 2018.

2.2 Ecosystem services

The concept of the ecosystem services has been the result from an intense debate during many years. Although there are many different definitions, they can be defined as “those aspects of the ecosystem used directly or indirectly to generate human well-being” [8]. Constanza et al. [3] were the first scientists who started the first classification. In spite of the fact that other researchers have created other lists since that moment, none of them always fit everywhere [9]. In this work, the Millennium Ecosystem Assessment list has been chosen owing to its international recognition. This Assessment was created by the NUO and it was agreed by scientists from more than 95 countries, being the most used one by the international organizations and public administrations [10].

Table 1. Ecosystem services considered in the study

In this work, the four groups of ecosystem services included in the Millennium Ecosystem Assessment have been valued. Each group have different ecosystem services depending on the characteristic of the ecosystem typology. Nevertheless, only the existent and relevant ones to the studied area have been considered (shown in Table 1), all of which chosen from the general list by considering the experts point of view.

2.3 Methodology

Both AHP and ANP allows us to calculate the importance or weight in percentages of each group of ecosystem services. In this case, all the ecosystem services have been valued individually when using ANP to consider all the relationship while only the four groups have been valued when using AHP. In order to compare the results resulted from each method; the ones obtained by ANP have been gathered in the four groups each service belong. The steps should be followed when valuating in AHP are explained by Saaty [12] while the ones related to ANP are explained by Saaty [13].

“The required judgments that are usually made in qualitative terms are expressed numerically. To do this, and not simply assigning a score out of a person’s memory; reciprocal pairwise comparisons are made in a carefully designed scientific way” [12, 13]. Therefore, the selected experts have prioritized the set of alternatives (ecosystem services) by using paired comparison matrices between their components following this method, all of which are listed below. The calculations have been done by using a self-software.

• Dept. of Vegetal Production. Polytechnic University of Valencia.
• Dept. of Agroforestry Ecosystems. Polytechnic University of Valencia.
• SEO-Bird Life (ecologist NGO)
• ‘Acció Ecologista Agró’ (ecologist NGO)
• Fishermen Community ‘El Palmar’.
• AVA-ASAJA Cooperative (farmer’s union).
• ‘La Unió’ Cooperative (farmer’s union).
• Appellation of Origin ‘Arròs de València’ Federation.
• Assut Foundation (public foundation)
• PAVAGUA (public company working on water sanity and environment)

All these people are professional biologists or engineers with technical and scientific knowledge in ecosystems so that the results are strong enough to be statically significant. They also show a broad vision of the social, ecological and economic reality of the area since the selected organizations encompass an important range of different points of view.

Judgments are given verbally as indicated in the scale of comparison established by Saaty [12, 13], which is shown in Table 2. “A corresponding number is associated with that judgment. The vector of priorities is the principal eigenvector of the matrix” [12, 13]. The resulting eigenvectors of the last matrices are indicating the weight of each alternative or ecosystem service.

Associated with the weights and the matrices, there is always mathematically an inconsistency. In both cases, it has been obtained by calculating the consistency ratio (CR). “Overall, inconsistencies are accepted below 10% for matrices of rank n > 4, 5% for n = 3 and 8% for n = 4” [12, 13].

Table 2. Scale of comparison [12, 13]

1. The Analytic Multicriteria Valuation Method has traditionally been based on the Analytic Hierarchy Process (AHP) and the Discounted Cash Flow. However, it can also be substituted by the Analytic Network Process (ANP). The first method is faster and easier whereas the second one is more accurate as it considers all the relationships between the different alternatives and criteria, although it involves a higher complexity.
2. Many ecosystem services are adding value to others, as there are many relationships between all of them. However, the cultural services hardly ever add value to the others although, on the opposite direction, those services (regulation, supporting and provisioning services) do add value to the cultural ones. This is why the cultural services are being overvalued when using AHP as this method is not considering these relationships and some value of the other services is being considered only in the cultural ones. The opposite fact happens with the regulation services as they are adding value to the other groups, but anyone adds more importance to it. Therefore, AHP is a method that is underestimating it.
3. The supporting and provisioning services have many relationships in both directions either between them or with the other two groups of ecosystem services so there is not any clear evidence whether AHP is overvaluing or underestimating them. The obtained differences are varying and depending on the expert’s opinion.
4. The differences obtained by using each method when valuating ecosystem services cannot easily influence the Total Economic Valuation as the food provisioning service (the reference one when calculating it) is not varying enough between AHP and ANP results. Nevertheless, more research should be done in these terms to ensure it as this was not the main goal of this study.
5. It is recommended to use ANP when valuating ecosystem services since it is more accurate and it considers all the relationships avoiding possible double counting.  However, new studies should be done in the future to corroborate it by using more experts and situations.