|Lange, H: Time series analysis of ecosystem variables with complexity measures, InterJournal for Complex Systems, 250 (1999)|
Natural forested watersheds are prototypes of ecosystems. They have a relatively well-defined boundary, closed cycles for fluxes of elements, contain a collection of species of all kinds of spatial sizes (microbes to trees), and are of important human concern as timber source and drinking water supply. They have been the focus of scientific investigation since many years now, and it seems to be a rather trivial statement that they exhibit rather complex behavior. Considering the amount of scientific knowledge gained, the intricate nature of food webs, transport mechanisms for matter and energy, growth and succession patterns, or responses to natural hazards, it almost occurs like a miracle that they are nevertheless manageable from a practitioner's point of view. Forestry has been working since centuries and has come up with simple empirical rules which allow timber yield predictions for a full rotation period (e.g. 80 years). Drinking water supply works properly in many cases. Science has not yet come up with an explanation for the existence or effectiveness of these empirical rules. Some of these rules are devaluated nowadays due to anthropogenic disturbances, e.g. in the context of forest decline symptoms. However, thus far science failed as well to give conclusive hints why these managing rules do not work properly. There is an obvious conflict between the managing and the scientific approach to such ecosystems. The reason behind this conflict is in our opinion the importance of the unique historical development of each given system (Hauhs and Lange 1996). They are rendered manageable by an effective biological reset, e.g. by planting operations, successive thinning etc., and thus a reduction or "amputation" of historical influence.