Total Environment Advances (2025)
The concept of ecological complexity transforms the way we conceptualise ecosystem entities, interactions, and processes. Restoring the complexity of ecosystems has been proposed as a principle for nature recovery activities. Yet, the use of the ‘complexity’ is inconsistent in different research, and lacks a generally accepted definition. This paper draws perspectives from various research fields to synthesise a cohesive concept of ecological complexity. We review a school of thought within the field of ecology, environment, and technical fields such as algorithmic complexity theory, information theory, chaos theory, and graph theory. We also summarise research methods framed by the complexity concept, and provide case studies on how restoration may benefit from the concept, philosophy, and methodology within the umbrella term. The complexity of an ecosystem includes the variety of species and the interactions among them or with environmental variables, with which the essential ecosystem functions, stability, and resilience are sustained. This concept indicates that species and ecological interactions are unified currencies of restoration. Meaningful assembly of species and interactions requires a deep understanding of each restoration project, and here we reflect on tree disease management, regenerative agriculture, species reintroduction, and seagrass systems. Complexity-framed research methods, ranging from systematic reviews to causal loop diagrams and individual-based models, help to integrate the best available information, understand how ecosystems operate, and examine alternative management policies.
