This study describes the analysis of two ecological systems of different sizes: Georgia State (USA) with 150,500 km2 and La Violada irrigation area (Huesca, Spain) with 0.5 km2. Systems analysis theory was used to interpret energy and matter flows in both systems and their environment. The conclusion is that external forces acting through human management drive both systems. First, they build an artificial environment and, secondly they use energy supplies as a subsidy or stress with either positive or negative effects.