|(übersetzt):||The ecological law of thermodynamics states that a system that receives a through-flow of exergy (high quality energy) will utilise the energy to move away from thermodynamic equilibrium in a process of self-organisation (JØRGENSEN 1997c). The capacity of ecosystems to self-organise is under way to become an important concept in environmental assessment. (KUTSCH et al. 2000). But for this purpose it is necessary to quantify the capacity of self-organisation. In the research sites of the Bornhöved-Project (Kiel Ecology Centre) several approaches of thermodynamic analysis of ecosystems were tested. A new method was developed in order to quantify the most important resource of ecological self-organisation: The exergy of solar radiation was assessed applying an approach analogous to the statistical interpretation of entropy (SVIREZHEV & STEINBORN 2001). Using data about short wave and long wave incoming and outgoing radiation, the solar exergy-flux into several ecosystems could be calculated. In comparison to crops and grassland ecosystems forests turned out to have a significantly higher ability to utilise the exergy of solar radiation. Other methods like the relative exergy uptake (SCHNEIDER & KAY 1994) or the entropy balance (AOKI 1987) seem to be less suitable for a differentiation between different ecosystems. As an integrating indicator of the effects of human activity on agroecosystems a model was used (SVIREZHEV 1998) providing a tool for the estimation of entropy balance. As a result we get a relative measure for different crops, which indicates weather the entropy of the site increases. A comparison of the years 1988 and 1997 showed that the overproduction of entropy decreased during these nine years on almost all fields in Lake Belau watershed. But still, there was an overproduction of entropy in 1997, too. It is not sure yet weather the applied concepts can be used as ecological indicators in environmental assessment. Continuous measurements are necessary observing the process of succession for a long time. With these results it will be possible to decide weather the self organisation of terrestrial ecosystems shows tendencies towards (for example) an increase of exergy flux from solar radiation.