Ecosystem accounts measure how ecosystems contribute to human well-being and the economy and how this evolves over time. If recorded in a consistent manner at different points in time, ecosystem accounts allow tracking the changes in ecosystems, including ecosystem extent and condition and ecosystem services (Obst et al. 2016).

Consistent and regular production of ecosystem accounts requires the development of best practice guidelines and testing these guidelines with pilot ecosystem accounts (Obst et al. 2013, Polasky et al. 2015). This is the objective of the System of Environmental Economic-Accounting – Experimental Ecosystem Accounting (SEEA EEA, United Nations et al. 2014). The SEEA EEA defines an integrated statistical framework for organising biophysical data, tracking changes in ecosystem assets, measuring ecosystem services and linking this information to economic and other human activity. The SEEA EEA framework consists of four core accounts. The ecosystem extent account organises information on the extent (total area) of different ecosystem types within an accounting area. The ecosystem condition account measures the overall quality of an ecosystem. Ecosystem service accounts measure the supply of ecosystem services, as well as their use by beneficiaries. The monetary asset account records the monetary value of ecosystem assets. Next to these core accounts, thematic accounts provide more detailed, quantitative data on, for example, land, water, carbon or biodiversity.

This framework for ecosystem accounts was formally adopted by the United Nations in March 2013 (United Nations et al. 2014) and technical recommendations are available to help set up and present accounts in a standardised way (United Nations 2019). The SEEA EEA and its technical recommendations are presently under revision, with the aim of adopting a revised standard for ecosystem accounting in 2021. This paper was developed as part of this revision process and contributes, in particular, to an updated set of recommendations for reporting ecosystem condition accounts.

Ecosystem condition has been defined in the technical recommendations (United Nations 2019) as the overall quality of an ecosystem asset in terms of its characteristics. The measurement of ecosystem condition has advanced since the SEEA EEA was adopted (see, for instance, Jakobsson et al. 2020 and Rowland et al. 2020) . However, there remains a lack of clarity on (1) precisely which characteristics are relevant in the monitoring of condition, (2) what indicators are most relevant to quantify ecosystem characteristics, (3) if and how indicators can be measured relative to a reference condition and (4) how ecosystem condition indicators can be aggregated across ecosystem types or across accounting areas.

The objective of this paper is therefore to collect and review existing ecosystem condition accounts that included information on the condition of various ecosystem types reported in a structured way, at a scale relevant for policy- and decision-makers and with explicit reference to SEEA EEA. When analysing these accounts, we addressed the following questions:

1. For which ecosystem types and realms is ecosystem condition reported?
2. What indicators or variables were used to develop an ecosystem condition account, what were the criteria to select particular indicators and were the indicators classified according to any typology?
3. Were indicators aggregated to single (or few) high-level indices or composite indicators to report an overall measure of ecosystem condition?
4. Was the information in the accounting table on ecosystem condition compared to reference levels for condition indicators or against a reference condition and, if so, what sort of information was used to determine a reference?
5. How was the account reported or structured: for example, was the account reported as area of ecosystem (ha or %) under a certain condition or were the condition indicators and/or aggregated index reported as opening and closing values?

These questions are addressed in this paper by reviewing, summarising and synthesising the information that is presented in a set of case studies included in this review. The final goal of this review is to better understand the current practices of countries, regions or organisations with respect to the development of ecosystem condition accounts. This understanding is needed to further guide the revision of the SEEA EEA and, in particular, to help prepare globally-accepted recommendations for standardised and consistent ecosystem accounts.

Selection of case studies

Almost all case studies come from Australia and the United Kingdom and from countries where English is an official language (Uganda, Canada and South Africa) or for a region where English is an official working language (EU). The Netherlands undertook an effort to translate the findings into English. Clearly, this review would have benefited from the inclusion of studies in other languages as well, if they had been available. All of the 23 studies reviewed are reports. Any studies that were published as scientific articles do not include account tables, presumably because they are considered too detailed and lengthy for academic journals. Most studies are undertaken or commissioned by governmental bodies and agencies. With one exception, all of the studies were published within the last six years (2013-2019), reflecting the fact that ecosystem condition accounting is a relatively-new field of practice. Of the 23 studies included in this review, 14 contained a structured condition table (also referred to as type A case studies, Table 1). These 14 studies came from five countries: Australia, Canada, Netherlands, South Africa and the United Kingdom.

The next sections analyse in more depth the results of the review following the structure outlined by the five research questions.

Realms, ecosystem types and assets, extent reporting

Ecosystem condition indicators, selection criteria and typology

Spatial and thematic aggregation of condition indicators

Reference levels and reference conditions

Reporting of the account

The way the condition account is reported is closely related to whether or not the account contains or is based on an aggregated index. There are two main ways used in the case studies to report the condition account (see Fig. 1 for a hypothetical example of both reporting systems). One method reports values of ecosystem condition indicators as opening and closing values per year, sometimes against a baseline year or a reference condition (case studies 1, 3, 5 and 6, Table 1). The second method divides indicators first into broad condition categories or classes on an ordinal scale, for example, from low to high condition (case studies 9 and 12, Table 1). This approach then breaks down the total ecosystem extent over these different categories either in absolute numbers, expressed in ha or km² or km length or as a percentage of the total area.

Figure 1.  

Two frequently-used reporting systems for the ecosystem condition account: reporting the opening and closing values of an indicator or index or reporting the total area or ecosystem extent under a specific ecosystem condition category. The data are hypothetical and only presented to illustrate both approaches to reporting the condition account.

Both reporting formats can be used to report on indicators, sub-indices or a single aggregated index or a combination of these.

Those ecosystem condition tables that included a measure of extent reported ecosystem extent in ha or km² or km length. This confirms that ecosystems are seen by the case studies as assets that can be measured by both extent and condition.

Good practice reporting was particularly observed in the South African river accounts (case study 9, Table 1) in the sense that they provide a complete set of accounts for sub-indices, condition category and condition index that allow tracking the different thematic aggregation steps. Sometimes, studies report only values and change of the aggregated indicators which results in a loss of information.

This review analysed 23 studies that report or discuss an ecosystem condition account at subnational and/or national scales. Fourteen studies published an ecosystem condition accounting table. The analysis of these 14 condition accounts produced a number of generalisations, which can provide information for the revision of the current set of technical recommendations to quantify and account for ecosystem condition at aggregated scales:

1. Most accounts report ecosystem condition for one or more ecosystem types, but there is little consistency in the terminology used to define ecosystem types;
2. All accounts report variables or indicators that measure specific ecosystem characteristics in order to make inferences about the overall condition of ecosystems;
3. All studies included biotic indicators and almost all studies included species-based indicators in the condition account;
4. The thematic aggregation of indicators into a single composite index (or into a few composite sub-indices) is not a standard practice, but applied in about half of the studies;
5. The definition and use of a reference condition or reference levels for specific indicators, against which the reported condition can be evaluated, is not a standard practice but was applied in about half of the studies.

Following points (4) and (5), countries using single composites were not more or less likely to also use reference levels or vice versa.

While there is no “one-size-fits-all” set of condition indicators that will work for all realms and all ecosystem types, there may be common indicators or common groups of indicators that can be used to assess ecosystem condition and reported in ecosystem condition accounts in a consistent way. This is particularly evident for species-based indicators which are used in almost all accounts. It demonstrates the importance of mainly locally-collected data about the diversity, occurrence and abundance of species in the understanding on ecosystem condition (Andreasen et al. 2001, Hatziiordanou et al. 2019, Kokkoris et al. 2018, Rendon et al. 2019). Besides using species as indicators for ecosystem condition, we note that the condition of marine and inland waters is frequently assessed using indicators that measure the physical or chemical state of water. In terrestrial ecosystems, ecosystem structure and function indicators, as well as landscape metrics, complement the species-based indicators to assess ecosystem condition. These general observations on how ecosystem condition is reported in an account could be useful to provide information for a common typology or classification for ecosystem condition indicators, which allows comparison of the condition of ecosystems across ecosystem types and across different spatial contexts.

The selection of indicators, used in the accounts that were analysed in this review, appears to be largely data-driven. Accounts are thus, in the first instance, compiled using the best available information and data. Such a data-driven approach likely explains the diverging typologies to classify indicators and the relatively-poor rationale found in the studies to explain use of particular condition indicators. It appears likely that the different ecosystem condition indicators have been grouped after they have been selected rather than the indicator selection being based on a predefined typology. A good practice is therefore to always provide a clear and explicit rationale for the selection of specific condition indicators and to identify any gaps explicitly. Clear selection criteria and justification of use of particular indicators also ensure that accounts are transparent, consistent and repeatable, particularly through time (for example, with different assessors). Therefore, it may prove to be useful to develop a common, hierarchically-structured typology of indicators, including abiotic and biotic indicators, to better guide the selection of a set of indicators that provide a comprehensive representation of condition.

As already mentioned above, only half the accounts considered in this review used a baseline or reference condition against which condition indicators were evaluated. A similar observation is made for aggregation, where only half the accounts included some sort of thematic aggregation, whereby different indicators are summarised in a sub-index or a composite indicator. Not all accounts that report a reference condition have aggregated condition indicators and vice versa, not all accounts that report a composite indicator have set a reference. We thus suggest that more guidance is needed on consistent levels of reporting, in particular if ecosystem condition needs to be compared across different accounting areas or across different ecosystem types. We also suggest that a tiered or stepwise approach to compiling the account with increasing levels of information (or complexity) is a practical way forward where outputs at each step are relevant for policy- and decision-making. For example, a three-tier approach could include the following: a tier 1 condition account that reports values for the key abiotic and biotic characteristics of ecosystems for each ecosystem type across an ecosystem accounting area for a particular year; a tier 2 condition account that includes a reference condition and allows users evaluating the current values of condition indicators against reference levels; and a tier 3 condition account that aggregates individual indicators into one or more composite indicators, facilitating communication about the overall condition of different ecosystem types and allowing relative comparisons amongst different ecosystems and different accounting areas.

An evident shortcoming of this review is its bias towards English-speaking countries. Furthermore, at least a few more studies have been published since the collection of the accounts considered in this paper. We particularly refer the ongoing work in Cyprus (Vogiatzakis et al. 2020), Bulgaria (Nedkov et al. 2018), Czechia (Vačkářů and Grammatikopoulou 2019) and Greece (Dimopoulos et al. 2017) as country case studies that base the development of condition accounts on a nation-wide mapping of the extent and state of ecosystems using a common methodology for the European Union (Burkhard et al. 2018).

Despite ongoing progress in ecosystem condition accounting, the limited number of studies that were available at the time of collection is evidence that the development of ecosystem condition accounts is still lagging behind, relative to the ecosystem extent accounts or ecosystem services accounts (e.g. Vallecillo et al. 2019). Clearly, a better understanding of ecosystem condition and more guidance to support its consistent measurement and reporting is needed to further boost the development and application of ecosystem condition accounts.

With respect to the five research questions addressed in this review, we suggest for revision of the SEEA EEA to (1) propose a globally consistent typology of ecosystem types, (2) provide guidance on selection of ecosystem condition indicators according to an agreed classification, (3) provide further guidance on aggregation methods and on the development of an ecosystem condition index that can be used to compare ecosystem condition across ecosystem types and across different accounting areas, (4) provide further guidance on how best to set reference levels for ecosystem condition indicators and reference conditions, against which the past, current and future ecosystem condition can be assessed and (5) propose a standard set of statistical tables for reporting the condition account.

The System of Environmental Economic-Accounting – Experimental Ecosystem Accounting (SEEA EEA) is going through a revision process between 2018 and 2021. The revised SEEA EEA is expected to be adopted by the United Nations Statistical Commission in March 2021. This article is based on a discussion paper that contributed to the revision process. The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official position of the SEEA EEA. The views expressed in this article do not reflect an official position of the European Commission.