Restrictions
Not all services are equally covered​
In the manual we try to be as complete as possible with regard to the various ecosystem services. Naturally, not enough information is available about all ecosystem services.
Some of the (mainly cultural) services are difficult to quantify because they concern people's feelings (social cohesion, identity, spiritual or religious meaning...). These services are best examined by using participatory processes.
A number of potentially important ecosystem services are not calculated within the Nature Value Explorer. Perhaps the most important of these are water quality regulation and flood prevention. These services are of great importance, but their complexity (physical and biological processes) as well as the current technical management within Flanders (Belgium) through, for example, water treatment stations, dikes, flood basins, etc. makes it impossible to obtain a somewhat reliable result with fairly simple models. However, there are some services that can serve as a proxy, such as nitrate removal through denitrification and water retention and infiltration, respectively.
In this manual we make as much use as possible of the latest knowledge in the field of valuation of ecosystem services, but the knowledge and substantiation are not the same for all ecosystem services. Therefore, some ecosystem services will be more detailed than others. For example, for the climate regulation service we can estimate how the value of this service will change in the future. We cannot do this for other services such as improving air quality. It is also not equally well known for all types of land use how they influence specific ecosystem services.
For some ecosystem services it is impossible to translate their valuation into a simple valuation function. We have indicated in the manual to which ecosystem services this applies and when more extensive methods and expert intervention are required.
The calculated total economic value as the sum of the values of the various ecosystem services in the Nature Value Explorer is therefore only a lower limit of the total value of the ecosystem.
Input data​
The results of the Nature Value Explorer are only as good as the data included in the quantification functions. We use a large number of public data layers. But these layers are often not updated annually and are therefore not always up to date with the current situation. This certainly applies to the drainage and groundwater maps. The user can manually adjust this data in the tool.
The input maps used can be consulted in another page of this manual and when discussing each ecosystem service separately.
Risk of double counting​
Some ecosystem services may overlap. One of the biggest challenges with valuation is avoiding double counting. A number of ecosystem services are difficult to separate from each other. The fact that a certain service is provided is often directly related to another service. Some examples: better water quality can contribute to drinking water production and fish production; impact on noise and air quality, for example, has an effect on health; pollination and agricultural production are strongly linked. This means that we cannot always clearly value all services separately and then add these values.
A good tool for this can be to divide ecosystem services into intermediate and final services (cf. Fischer 2007). The intermediate services are the functions (supporting, regulating) that make an important contribution to the final ecosystem services with benefits for society. Retention of water can, for example, contribute to protection against flooding. We only have to appreciate the final services. If these are difficult to value, the intermediary service can be valued as a proxy.
Although we have tried to avoid double counting as much as possible, users should still pay due attention to this when interpreting the results.
Uncertainty when transferring values to other areas​
The tool partly uses benefit transfer. Attention to differences in context is important. The values are only valid for the preconditions stated for each ecosystem service. To minimize differences as much as possible, we use statistical valuation functions where possible that integrate spatial factors as much as possible (both ecological factors that influence natural processes and factors that influence people's willingness to pay).
The Nature Value Explorer was mainly built for areas within the Flemish region.
The cultural value through the stated preferences only relates to nature development within Flanders and is based on the willingness to pay of Flemish families. Also for the regulating services, with the exception of the improvement of air quality, the calculations have been drawn up based on Flemish situations and are mainly derived from Flemish classification methods for soil, groundwater,...
In 2020-2021, the methods were also examined for usability for Wallonia. A number of adjustments were made to the numbers used to increase applicability for Wallonia.
The use of the Nature Value Explorer for areas outside Belgium must be done with great caution, but it is possible if it concerns a comparable ecoregion. It is true that the input data required for the calculations is not present and the user has to enter the input data himself. This is not always obvious since, for example, we often work with soil characteristics that have their own coding in Belgium.
The results must also be treated with caution when it concerns a border area. E.g. for recreation, any visitors to the border area outside Flanders are not included.
Other restrictions​
The manual does not offer cost-benefit calculations. We have tried to briefly indicate what steps still need to be taken in order to use the figures in a cost-benefit analysis.
To collect the necessary data, the tool uses maps whose data may be several years old. The reality may have changed in the meantime compared to this data. For example, the drainage class of an area may have changed compared to what can be found in the soil map. If experts know how things have changed, it is advisable to use this knowledge to determine the quantities. If existing data is used or adapted, it is important to clearly state the reference situation and the assumptions made in the report.
The tool also does not provide advice on how to separate project benefits from benefits that would have occurred without the project (autonomous change). Properly describing the reference situation and the assumptions made regarding, for example, autonomous changes is crucial.