At least two accounting systems for Gross Ecosystem Product (GEP) are needed

Gross Ecosystem Product (GEP) denotes the aggregate value of ecosystem services (ESs) supplied by all ecosystem types within an accounting area for a given accounting period in monetary units and represents one of the multiple types of measures of ES values. The value of each ES is typically calculated by multiplying the ES's quantity by the ES's unit value that may be reflected by various proxies, such as market price, replacement cost, and avoided damage cost. As an economic, ecological, or environmental indicator, GEP should be calculated based on certain standards, allowing for comparison over time and across regions. While many standards, including which ESs to account for and what proxies for ESs' values to use, should be unified to improve the comparability of GEP, this standardization does not mean a single GEP accounting system is sufficient to achieve multiple goals. Instead, at least two accounting systems with different applicability and levels of sophistication are needed. (1) To assess environmental status, ecosystems' capacities to provide ESs, and the performance of environmental governance, there should be a simplified system that accounts for both realized ESs (actually received by humans) and potential ESs (beyond actual humans demands) and adopts a nationwide unified constant unit value of each ES. (2) To assess ESs' actual contributions to socioeconomic development and human well-being, there should be a more sophisticated system that accounts for realized ESs only and adopts a dynamic unit value of each ES. This dynamic unit value should be adjusted to fit local socioeconomic and ecological contexts, consider the tipping point or threshold in each ES's quantity, and reflect the diminishment or increment in the marginal utility of each ES.