抄録
In this report, I discussed what a healthy ecosystem means from my own experience. I think that ecosystem health is determined by the conditions under which "the organisms that should be found in that ecosystem can properly survive". Then, what sorts of species, species assemblages, local populations and individuals are those "that should be found there"? Does "properly survive" mean that the standing crop is bigger than certain size? Can they complete the life cycle? Don't they become extinct in the course of natural fluctuations in abundance? In order to answer those questions, we should consider with historical changes of the natural environment and interactions between people and water environments. It is clear that evaluation and restoration of "healthy ecosystem" should be based on mutual relationships between nature and human beings.
