Geographical and ecological differentiation of Fagus forest vegetation in SE Europe

Questions What is the main syntaxonomical pattern within beech forests in SE Europe? What macroecological and ecological factors distinguish these forests? Location SE Europe: Balkan Peninsula, from the SE Alps in Slovenia, through Croatia, Bosnia and Herzegovina, Serbia, Montenegro and the Republic of Macedonia to N and NE Greece and Bulgaria, covering ca. 400 000 km2 over a length of 1000 km. Methods With a view to differentiating beech and beechfir forests, a data set of 5952 published and unpublished phytosociological releves were surveyed. After stratification, 997 releves remained. Cluster analysis of the data set was used to calculate diagnostic species for each cluster. Ecological indicator values (EIV) were used to estimate ecological conditions. Average EIV, altitude, latitude and longitude for releves of each cluster were plotted in a detrended correspondence analysis (DCA) diagram for ecological interpretation of clusters and relationships between clusters. Correlations between DCA releve scores and explanatory variables (EIV, portion of life forms and chorotypes, altitude, latitude and longitude) were subsequently calculated. Results Cluster analysis divided mesophilous beech forests of SE Europe into two major clusters. Beech forests can therefore be classified into two alliances, Aremonio-Fagion and Fagion moesiacae. Further division revealed seven beech and beechfir forest types, which we interpreted geographically and ecologically. A significant increase in the proportion of chamaephytes, hemicryptophytes and therophytes was detected along the main macroecological gradient towards the S and E. At the same time, the proportion of geophytes and phanerophytes significantly decreased in the same direction. There was also a significant increase in the proportion of Stenomediterranean, Eurymediterranean, Mediterranean-Montane, and Eurasian species, while Boreal species, as expected, decreased toward the southeast. The main differentiation of beech forests in SE Europe is due to macroecological factors (macro-climatic and historical development of vegetation), whereas local ecological factors (particularly temperature and moisture) are reflected in the differentiation of sub-alliances. Conclusions Our study confirmed two major groups of beech forests in the research area, which could be classified into two alliances. It also revealed that there is not just an altitudinal distribution of beech forests in the SE part of the research area, but also structural and functional changes of communities as a result of the altitudinal limitation of beech forests and changed macroclimatic factors.