Researches, studies and analysis of ecosystem services are not sufficient if we want to use them for environmental management and territorial development: in these cases, we have to assess ecosystem services. Assessment describes the analysis and reviews the information derived from research, in order to help those holding responsible positions in recognizing problems and evaluating possible actions. Assessment means assembling, summarising, organising, interpreting and possibly reconciling pieces of existing knowledge and communicating them so that they are relevant and helpful to an intelligent but inexpert decision-maker.

A successful assessment accounts for the multi-dimensionality of ecosystem services and considers them in an integrated way by taking into account their interactions with and reciprocal effects on social-ecological systems. The interdependence of ecosystem services can be shown by the example of agriculture. Intensive agricultural practices to enhance the service of food provision has led to the depletion of agricultural lands and the loss of biodiversity, thus affecting regulating services such as soil formation, gene pool protection and certain cultural services as well.

On the other hand, ecosystem service mapping is the creation of a cartographic representation of ecosystem services in a geographic space and refers to a specific time. Mapping is a method of making the information derived from the assessment process visually accessible, especially to inexpert users. This visual representation can be made through indicators.

Depending on scale and extent of information, a figurative representation (charts, diagrams) can also be sufficient.

As our understanding of ES continues to grow, finding ways to explicitly identify and measure their condition, trends and rate of change is an important step towards integrating ES into decision-making. To assess these different types of ES and efficiently communicate information about their characteristics and trends, indicators are used.

An indicator is a quantitative measure that represents a complex system or phenomenon.

In our case, indicators are used to monitor the state and trends of ecosystems and the ecosystem services delivery within a determined time interval.

Since ES provide many types of benefits to humans, indicators using biophysical, economic and social valuation methods can all be employed for their measurement. Biophysical units are used to measure quantities or features directly connected with ecosystem structures, processes and functions. Some examples are the volume of water runoff from sub-catchment areas or the amount of nitrogen filtered by the ecosystem. On the other hand, indicators with economic and social units are mainly used to quantify benefits and values that humans obtain from ecosystems, such as the monetary value of a certain ecosystem for tourism or outdoor recreation.

These examples illustrate how indicators can simplify the evaluation of a complex system and enable its graphic or spatial representation. Through the calculation and analysis of ecosystem services indicators over time, we can understand trends in complex ecological processes and monitor sustainable development.

Depending on the type of ecosystem services, but also on other criteria, not least the availability of time and of financial resources, different assessments of ecosystem services are possible, with the aim of providing reliable results. In all cases, however, the objective is to acquire information for the creation of suitable indicators. The three types of assessment are described below.

Biophysical assessment

Within biophysical assessment ES indicators can be quantified via direct and indirect measurements as well as modelling approaches.

• Direct measurement of ES is performed by assessing physical units that correspond to the units of the indicator, e.g. measuring the amount of water abstracted from ground water layers (water provision).
• Indirect measurement uses data that need further interpretation, combination, modelling, assumptions or processing. Typical data sources are remote sensing data with their derived products like NDVI, surface temperature, land cover classifications, etc.. Subsequently, local climate regulation can be deduced from explicit patterns of surface temperature.

Socio-cultural assessment

Socio-cultural valuation refers to the contribution of ecosystem services not only to monetary benefits but also to societal issues in terms of cultural, therapeutic, artistic, inspirational, recreational, educational, etc. values. There are different methods, and some examples are listed below:

• Preference assessment is performed through interviews, ranking exercises and scenario selection of ES impacting measures analysing knowledge and perception of individuals.
• Photo-elicitation surveys translate individual visual experiences valued by the taking of a photograph of e.g. a landscape into ES values.
• Participatory mapping also referred to as PGIS (participatory GIS) builds a knowledge system to which various stakeholders can contribute with their information about the location and quality of certain ES.
• Scenario planning combines various methods to illustrate the links between alternative futures, changes in ES and human wellbeing.

Expert assessment

Ecosystem service science lies between the sciences of applied ecology, economy, sustainability and the social sciences. This combination makes it very complex and it is worth involving experts from these fields and with experience in transdisciplinary work. Experts can fill gaps in data. They generate quick results through their knowledge, with a minimum of resources and finances. Furthermore, the involvement of experts increases the credibility of results.

The engagement of experts happens on several levels. During the scoping phase, objectives for the mapping, maps and their application are set. With method selection and design, the technical aspects of the assessment are settled. The creation of reliable maps ensures the transparency, readability and interpretability of the maps to be produced. Application and implementation will be tested by experts in accordance with the set objectives.