This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Questions What are the main floristic patterns in European beech forests? Which classification at the alliance and suballiance level is the most convincing? Location Europe and Asia Minor. Methods We applied a TWINSPAN classification to a data set of 24 605 relevés covering the whole range of Fagus sylvatica forests and the western part of Fagus orientalis forests. We identified 24 ‘operational phytosociological units’ (OPUs), which were used for further analysis. The position of each OPU along the soil pH and temperature gradient was evaluated using Ellenberg Indicator Values. Fidelity of species to OPUs was calculated using the phi coefficient and constancy ratio. We compared alternative alliance concepts, corresponding to groups of OPUs, in terms of number and frequency of diagnostic species. We also established formal definitions for the various alliance concepts based on comparison of the total cover of the diagnostic species groups, and evaluated alternative geographical subdivisions of beech forests. Results The first and second division levels of TWINSPAN followed the temperature and soil pH gradients, while lower divisions were mainly geographical. We grouped the 22 OPUs of Fagus sylvatica forests into acidophytic, meso‐basiphytic and thermo‐basiphytic beech forests, and separated two OPUs of F. orientalis forests. However, a solution with only two ecologically defined alliances of F. sylvatica forests (acidophytic vs basiphytic) was clearly superior with regard to number and frequency of diagnostic species. In contrast, when comparing groupings with three to six geographical alliances of basiphytic beech forests, respectively, we did not find a strongly superior solution. Conclusions We propose to classify F. sylvatica forests into 15 suballiances – three acidophytic and 12 basiphytic ones. Separating these two groups at alliance or order level was clearly supported by our results. Concerning the grouping of the 12 basiphytic suballiances into ecological or geographical alliances, as advocated by many authors, we failed to find an optimal solution. Therefore, we propose a multi‐dimensional classification of basiphytic beech forests, including both ecological and geographical groups as equally valid concepts which may be used alternatively depending on the purpose and context of the classification.

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 beech–fir forests, a data set of 5952 published and unpublished phytosociological relevés were surveyed. After stratification, 997 relevés 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 relevés of each cluster were plotted in a detrended correspondence analysis (DCA) diagram for ecological interpretation of clusters and relationships between clusters. Correlations between DCA relevé 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 beech–fir 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.

No abstract

No abstract