Timberlines of the Greek high mountains: status quo at the turn of the millennium

The present review article provides an overview about the timberlines of the Greek high mountains. It informs about the existing tree species and about the altitude, physiognomy and dynamics of the timber-line ecotones. Subsequently, it gives an interpretation of the human influence and the geo-ecological factors, which may have caused the altitudinal limit of tree growth in Greece. A latitudinal and local change in timberline-forming tree species creates high heterogeneity between the research areas and makes this their most remarkable feature. Moreover, in Greece there is no rise in timberline altitude from north to south. In some areas, fir-dieback causes a local decline in timberline altitude, which is the predominant dynamic process. An anthropogenic depression of the forest line is certainly common. Yet, a natural forest cover reaching up to the peak zones of the Greek high mountains is unthinkable. The identified timberline-forming factors and the prevailing site conditions speak against this. In accordance with the Mediterranean climate regime, it is obvious that not only the climatic conditions of winter (frost, snow) determine the limits of tree growth. The (macro- and micro) climatic impacts of summer (drought, high insolation) play a highly important role as well. Against this background, the climate-ecological hindrances to the establishment of trees, i.e. the germination and the survival of seedlings, are identified as key-factors for understanding the Hellenic timberlines (“regeneration hypothesis”). Against the background of global warming, suggestions for further research on the ecology and dynamics of the Greek high mountain timberlines are provided.