Drought effects on the floristic differentiation of Greek fir forests in the mountains of central Greece

Abstract: Greek fir (Abies cephalonica Loudon) grows in montane Mediterranean climates characterized by dry, warm summers. Drought is an important climatic feature of these montane ecosystems as it affects the floristic composition, structure and distribution of plant communities. The Oxia-North Vardousia mountain system is one of the few areas in Greece with an extensive, well-preserved Greek fir forest. This study aims at describing the Greek fir forest vegetation of such area and determining the drought-related factors affecting their floristic composition and differentiation. Vegetation releves were classified and ordinated. The impact of drought-related variables on the vegetation composition was analyzed. A cluster analysis was used to reveal the most important factor for the discrimination of the main plant communities and to determine the drought threshold between them. Two plant communities that reflect the differentiation of the Greek fir forests in central Greece into xerophytic and mesophytic forest communities were described. Each community was divided into two sub-communities. The elevational distribution of Greek fir forests in the mountains of central Greece follows a drought gradient linked to the two main climatic components of drought, precipitation and potential evapotranspiration. The combination of these two drought-related variables into a suitable humidity index was found to adequately differentiate the xerophytic from the mesophytic forest communities and define their drought threshold.