From the case study of model validation using the Soppen-see pollen proxy data we concluded that paleo ecological validation of forest ecosystem models offers on one hand promising potentials, yet suffers at the same time from strong limitations. Paleo eco logi cal proxy data are the only data sources that offer long-enough time series of unmanaged forest dynamics. Moreover, with paleoecological data we can validate forests under a climate that changed at various rates, so increasing our confi dence that the model behaves realistically under scenarios of fu ture climatic change. There are still strong limitations to a paleoecological model validation, as for instance became evident from the many uncertainties outlined in the present study. A failure of the validation may be due to errors in the ecosystem model, e.g. wrong parameter values, as well as due to errors in the reconstruction of the past climate or the past vegetation.
Further uncertainties remain because of the unknown nature of the pollen source area in the past.
It could be used to replace the transfer functions often used to re con struct past vegetation compositions. Thirdly, models of tree mig ration are highly needed, since migration potentially plays a key role in the transient forest responses to climatic change, especially during phases of strong climatic changes such as the end of the last ice age and as projected for the following century. Due to current data limitations respectively not yet fully developed methods of generating bioclimatic scenarios at any ecological interesting site, our results remain restricted to the few presented case studies. Hence, no uniform, simple response of the mountain forests to a climatic change is to be expected. Biggest sensitivities were found in areas which border a continental climate already in the present and in sub-alpine conditions.