Towards a standardised monitoring of ecosystem condition: A literature review on indicators and their data sources

• We present a variety of approaches and common themes in recent literature assessing ecosystem condition (EC). • 302 articles met the criteria of using spatially explicit indicators to assess EC. • We summarise key ecosystem characteristics represented by EC indicators and the data types used to develop them. Easily updatable information on ecosystem condition (EC) is essential for understanding trends in ecosystem degradation and prioritising restoration efforts. However, assessing the state, health, or quality of ecosystems is a complex and multidisciplinary challenge, resulting in a wide array of approaches documented in the scientific literature. With growing emphasis on international restoration targets and discussion on how to effectively address EC within established accounting frameworks, the need for robust, systematic methods for assessing EC is increasingly evident. This study reviews recent applications of spatially explicit indicators for mapping EC, with the aim of highlighting the main indicators used in research and related data sources. We find that certain ecosystem types, such as forests, are assessed more frequently, and that most indicators employed reflect structural attributes of ecosystems. Compositional and functional characteristics remain comparatively underexplored. We show that the data used to develop metrics vary across ecosystem types, but remote sensing is widely used to develop spatially explicit and continuous indicators. Our results provide valuable insights on the challenge of comprehensive and systematic assessment of EC, and can stimulate discussion on potential minimum sets of indicators for EC. We highlight future directions for research in this field which would allow for a more complete and robustly informed use of indicators, supported by well-established data-to-indicator pipelines.