Exergy versus emergy flow in ecosystems: Is there an order in maximizations?

From ecosystems theory, orientors have been derived to give a holistic view of the trend of development of ecosystems themselves. Several principles of maximization, mainly derived from Lotka's maximum power, are connected with these orientors. Other authors (Jorgensen, Patten and coworkers, for example) have shown that among these orientors there are many common aspects, both form a quantitative terms and in principle. We show how H.T. Odum's maximum empower and Jorgensen's maximum exergy principles can be both valid from a practical viewpoint. As suggested by a simple experiment there can be a time order: first the maximization of empower and then the maximization of exergy. This time sequence is also consistent with a maximization trend in the ratio of exergy to empower. (C) 2005 Elsevier Ltd. All rights reserved.