Complex Response: An environmental reaction to change that occurs at multiple levels to multiple objects, and can induce a chain reaction of responses to a single initial change.
The reaction to a change at multiple, and possibly unforeseen, levels. This could include a chain reaction of responses to a single initial change, resulting in a complex set of results, which in turn, could lead to more, and again possibly unforeseen, change. Succinctly, it is akin to the butterfly effect: one small event (change) can cascade through a given system creating new agents of change, and operating at several levels.
The term complex response in most commonly used in fluvial geomorphology, or the study of river systems and changes within those systems.
References
Complex response Wikipedia(Text) CC BY-SA