Mapping and assessing forest ecosystem condition in Lithuania

The System of Environmental-Economic Accounting – Ecosystem Accounting (SEEA-EA) is a standard statistical framework developed by the United Nations and adopted in 2021. SEEA-EA aims to integrate the natural value of ecosystems in both physical and economic terms through ecosystem accounts. Physical accounts include ecosystem extent (e.g., extent of an ecosystem type), ecosystem condition (EC) (e.g., the health/ecological status of an ecosystem), and ecosystem services (e.g., carbon sequestration). Monetary accounts include ecosystem services (e.g., economic valuation) and assets. Forests play an important role in the socio-economic dynamics of many countries by providing multiple ecosystem services that support human well-being. In the context of SEEA-EA, forests are among the most-studied ecosystem types. However, most studies focus on ecosystem extent (e.g., forest cover changes) and ecosystem services (e.g., carbon sequestration). Less attention has been paid to EC, despite its importance in fully disentangling the link between ecosystem status and the supply of ecosystem services. In this study, we map and assess forest EC at the Lithuanian national scale and analyse changes over time by comprising two periods (2021 and 2024). In the SEEA-EA, EC is assessed based on abiotic, biotic, and landscape ecosystem characteristics, as defined by the SEEA-EA Ecosystem Condition Typology. Based on the literature, we defined three ecosystem variables for the ECT class, totalling 18 variables (e.g., tree cover density, soil organic carbon). The reference conditions for forest ecosystems in Lithuania were defined based on forests under strict protection. Based on these reference areas, the 18 variables were rescaled to 0-1 using the SEEA-EA methodological guidelines. The final EC index was calculated by overlaying the 18 indicators and assigning equal weights to each. The results showed higher EC values across Lithuania, particularly in the central and western parts of the country, which were associated with large, contiguous forest patches. Low EC was found in areas with smaller forest patches, mainly in the central, eastern, and western parts of the country. Regarding differences across years, the overall median EC index was higher in 2021 than in 2024. This can be attributed to changes in indicators that were not static (e.g., Leaf Area Index), which highlights both the advantages of remote sensing (e.g., large area cover and capacity to detect changes over time) but also influences the results (e.g., problems with cloud coverage for large areas such as national scale). Overall, this study is the first effort to map and assess forest EC beyond previous efforts to implement the SEEA in its experimental phase, serving as a basis for further development and improvement. The results obtained contribute to enhancing knowledge of the ecological status of Lithuanian forests, providing insights and guidance to support the implementation of SEEA-EA in Lithuania, which is envisaged within European environmental directives and policies.