Theory of stepwise ecological restoration

The United Nations General Assembly declared 2021–2030 as the "Decade of Ecosystem Restoration", which positions "the restoration of ecosystems as a major nature-based solution towards meeting a wide range of global development goals and national priorities". Ecological restoration, when it was implemented effectively, contributes to improving food and water security, mitigating climate change, protecting biodiversity, boosting economic prosperity and benefiting human health and well-being. Thus, ecological restoration is fundamental for the success of ecological civilization and sustainable development. Ecological restoration theories in developed countries usually require restoring the ecosystem to the status prior to degradation, and this requirement is difficult to achieve in regions with serious degradation, especially in developing countries. We developed a new theory of ecological restoration, or stepwise ecological restoration (STERE), which comprises three modes in different restoration stages: Environmental remediation in the initial stage with serious degradation, ecological rehabilitation for moderately degraded ecosystems, and natural restoration for slightly degraded ecosystems. Environmental remediation aims to reduce environmental pollution through the removal or detoxification of pollutants or excess nutrients from soil and water. Ecological rehabilitation is the process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed through various physical, chemical and biological restoration strategies. Natural restoration aims to restore ecosystem functions and services and improve ecosystem resilience without much human assistance. Environmental remediation is fundamental and needs to be implemented prior to ecological rehabilitation and natural restoration in places where pollution is severe. Only the former is successfully carried out; however, when the ecosystem is moderately degraded, ecological rehabilitation can be effectively implemented. In places where the ecosystem is slightly degraded, natural restoration is recommended. The processes of ecological rehabilitation and natural restoration will result in ecological functions that are more complete, an increase in biodiversity, and improved ecosystem resilience. For STERE, appropriate restoration goals should be formulated based on the degree of degradation, local funding support, and technological development. The new theory proposed in this study emphasizes the application of reference ecosystems in restoration projects and the importance of ecological monitoring. It also requires an adaptive restoration management framework that considers the influence of global climate change. STERE should be implemented for future ecosystems rather than only for restoring an ecosystem to a status similar to the condition prior to degradation. Moreover, STERE promotes systematic large-scale landscape restoration by considering the interactions between individual small scales (e.g., field scale) and large scales (e.g., catchment scale). In addition, technologies such as unmanned aerial vehicles and remote sensing should be more widely used in future STERE projects. Ecological restoration databases should be established for restorative activities in mountains, waters, forests, farms, lakes and other ecosystems. The newly proposed STERE theory would play an important role in developing restoration projects worldwide, especially in developing countries.