Indicators of success for ecosystem restoration depend on a proper assessment of the extent to which human activity has degraded biodiversity and ecosystem functions and services. In the run-up to the 13th Conference of the Parties on the 2020 Aichi biodiversity targets this year in Cancún, Mexico, we suggest how such assessments could be improved and standardized globally.

The current state of ecosystems is measured by using direct observations. To detect trends in degradation or recovery over time, we must also define a baseline reference state. However, an arbitrarily chosen baseline, such as 50 years ago, might not reflect the true magnitude or direction of land degradation or recovery.

Instead, we suggest using an ecosystem's pre-degradation state, also known as its natural state. This state has no human-caused loss of biodiversity or of ecosystem functions. Contrasted with the ecosystem's current state, it provides a robust indicator of damage or recovery. It is determined by scientific research, but should not be viewed as a restoration target — those are merely political goals that balance social, economic and ecological interests.

A pre-degradation baseline could provide a universally applicable reference state. It reflects the deviation from genuine sustainability and, as a global standard, would ensure the fairness and comparability of ecosystem assessments across countries that are in different phases of economic development.