Question: Which are the gradients of floristic differentiation in Greek beech (Fagu sylvatica) forests? Which is the role of geographical and ecological factors in this differentiation?

Location: Beech forests of the plant geographical regions Northeast, North Central and East Central Greece.

Methods: A total of 1404 published and unpublished phytosociological relevés were used in the analyses. TWINSPAN and DCA were applied to classify and ordinate the relevés. Altitude, Indicator Values of relevés and their X and Y coordinates were used in a posteriori interpretation of the ordination axes. Kendall's correlation coefficients were calculated between DCA relevé scores and explanatory variables. Multiple linear regression was used to partition the variation explained by the first two DCA axes, between the geographical and the ecological variables.

Results: Classification resulted in 14 vegetation units defined by species composition. Two types of gradients, ecological and geographical, were revealed by the DCA of all relevés. The partition of the variation accounted for by the first and second DCA axis was attributed mainly to ecological and geographical variables, respectively.

Conclusions: Beech forests of northeast and Central Greece show phytogeographical differences, while ecologically similar vegetation units occur in both regions. A west-east gradient is revealed in Greek beech forest vegetation. The extent of the study area, its position along regional gradients and the comprehensiveness of the data set that is analysed determine the types of the gradients which can be revealed in a vegetation study.

Nomenclature: For names of mountains: Strid & Tan (1997). For names of plant taxa: Tutin et al. (1968–1993); Greuter et al. (1984–1989); Strid (1986); Strid & Tan (1991, 1997, 2002).