As it was mentioned, both social systems and ecological systems are considered as complex system due its emergency and the interaction among their agents. But also the system composed from the imperative relation among them is indeed a complex system. More precisely a Complex Adaptive System. Actually, this relation has a great importance due to the increasing threaten from the human systems towards the ecosystems. This system has been named as Social-Ecological-System (SES).

The SESs have a hierarchical base, and the sustainability depends on the interactions of this hierachical structure.  Then before an assessment of the sustainability could be made, is necesary to understand how this system is composed. This means that the definition of the interacting agents in both, the social system and the ecosystem, is needed.

The sustainability of each natural resource is a function of the interactions among the internal and external factors. The internal factors may be social, political, ecological, or economic; while the external factors include foreing debt, structural poverty, gobal environmental problems, and social/political/economic conflicts. For all internal factors have been assigned indicators of sustainability and for the external ones have been identified a set of attributes (1).

All of this interactions among internal and external factors increments the complexity of the SES’s sustainability.

(1) Holling, C.S., “Understanding the Complexity of Economic, Ecological, and Social Systems” Ecosystems (2001) 4:390-405.