AbstractsGeography &GIS

This study aimed to describe the Greek fir forest vegetation of the flysch area in Oxia-North Vardousia mountain range in relation to drought. It also applied and compared two different methodological approaches for the quantification of drought. The quantification of the most important environmental thresholds for the occurrence of the different forest vegetation units were also assessed.Two methods were used to quantify the drought: a humidity/aridity index (HI), which incorporates only the climatic components of drought (climatic drought); a more complete, water balance, method that includes, additionally, the soil components of drought (site drought). The spatial quantification of drought for the whole study area was assessed with the use of HI. The HI was calculated for different time periods and the values for the vegetation period were used for the stratification of the study area. Geostatistical methods were used for the spatial prediction of temperature and precipitation, and a GIS-based model for the calculation of solar irradiation. For the estimation of reference potential evapotranspiration (PETref) an empirical equation was chosen after a careful evaluation of its performance. The description of fir forest vegetation was based on floristic, structural and abiotic parameters recorded in 45 relevés. For the sampling the area was stratified based on the climate conditions during the vegetation period, and the locations of the plots in each stratum were randomly selected. The soil hydraulic properties were derived from soil profiles and laboratory analysis of undisturbed soil samples. Vegetation relevés were classified with cluster analysis and vegetation units were defined and compared with existing published relevés from central Greece. Gradient analysis was performed with the use of non-metric multidimensional scaling. The vegetation pattern was analyzed with several drought-related variables and other abiotic and biotic variables. Classification trees were used to determine the most important environmental factors and to quantify their limits between the Abies forest vegetation units.Two forest communities (Crepis fraasii-Abies cephalonica comm. and Sanicula europaea-A. cephalonica comm.), including four subtypes, were identified within the Abietion cephalonicae alliance, related to a drought gradient. The Crepis fraasii-Abies cephalonica comm. occupied the driest side of the gradient, in contrast to Sanicula europaea-A.cephalonica comm. which occupied the moister sites. The syntaxonomy and nomenclature of those units was discussed as well as their affinities with other Abies vegetation units from central Greece. Humidity index followed by potential evapotranspiration were found to be the most important variables for the discrimination of the two forest communities. The Crepis fraasii-Abies cephalonica comm. occurs when HI is < 0.26 for the four driest months or when PETref is > 1034.3 mm for the growth period. For values of HI > 0.26 or PETref < 1034.3 mm the Sanicula europaea-A. cephalonica comm.…