Plant Biosystems, 2013 Vol. 147, No. 1, 84-98, http://dx.doi.org/10.1080/11263504.2012.717550 Taylor & Francis Taylor & Francis Group Ecological and phytogeographical differentiation of oak-hornbeam forests in southeastern Europe P. KOŠIR1'2, S. CASAVECCHIA3, A. ČARNI1'4, Ž. ŠKVORC5, L. ZIVKOVIC3 & E. BIONDI3 1 Institute of Biology, Research Centre of the Slovenian Academy of Sciences and Arts, Ljubljana, Slovenia; 2 UP Famnit, University of Prímorská, Koper, Slovenia; 3 Department of Agriculture, Food and Environmental Sciences, Marche Polytechnic University, Italy; 4School for Viticulture and Enology, University of Nova Gorica, Nova Gorica, Slovenia; 5Faculty of Forestry, University of Zagreb, Zagreb, Croatia Abstract The aim of the study was to establish the main types of oak-hornbeam (Carpinus betulus and Quercus sp. div) forests on the Apennines., Balkan peninsula and southern Alps and their correlations with the main ecological and phytogeographical gradients in the region. Furthermore., the comparison with the major types recognized in the traditional expert-based classification was done. 1676 releves of oak-hornbeam forests (alliances Erythronio-Carpinion, Carpinion moesiacum, Physospermo verticillati-Quercion cerris) from the area of the Apennines., Balkan peninsula and southern Alps were collected and entered in a Turboveg database. 508 releves remained after stratification and were classified with a Modified Two Way Indicator Species Analysis, which resulted in four main clusters that are phytogeographically interpretable, such as (1) southern Apennines, (2) northern-central and central Apennines, (3) central-southern Balkan and (4) north-western Balkan and southern Alps, further divided into subclusters. Pignatti indicator values calculated for releves of each subcluster were subjected to PCA in order to show the ecological relationships among subclusters, and the spectra of geo-elements were calculated to show the phytogeographical relationship between them. The diagnostic species combination was calculated by a fidelity measure (phi-coefficient) and presented in a synoptic table. Synsystematic classification of the elaborated groups is proposed. Key words: Apennines, Balkan peninsula, biogeography, Carpinus betulus, ecological and phytogeographical gradients, Quercus sp. div., southern Alps, syntaxonomy Introduction The center of distribution of oak-hornbeam forests as zonal vegetation lies in subcontinental areas of east-central Europe and southeastern Europe, in lowlands, hills, and the low mountain belt (Bohn et al. 2003). In southeastern Europe, the vegetation of oak-hornbeam forests is zonal in the northern part of the Balkan peninsula as far as river the Drina on the southeast and in northern Italy till the Padanian plain. Actually, in the Padanian plain (Po valley) this kind of vegetation was zonal but is now virtually extinct {Querco-Carpinetum boreo-italicum Pignatti 1953 =Asparago tenuifolii-Quercetum roboris (Lausi 1966) Marincek 1994). On the Apennines and in the central-southern part of the Balkan peninsula, this vegetation is extrazonal and is edaphic-orographic conditioned (Kojic et al. 1998; Marinček & Carni 2000; Biondi et al. 2002, 2008). In central Europe, these forests are classified into the Carpinion betuli alliance (Oberdorfer 1992, Knollová & Chytrý 2004; Willner & Grabherr 2007). For mesophilous deciduous forests of southeastern Europe it has already been established that they differ from forests in central Europe, and vicariant alliances (suballiances) have been described within the order Fagetalia sylvaticae. Therefore, the southeastern European alliances Erythronio-Carpinion (occurring in the Apennines and Balkans), Physospermo verticillati-Quercion cerris (occurring in the southern Apennines) and Carpinion moesiacum (occurring in the central-southern Balkans) are vicariant to the central European alliance Carpinion betuli Correspondence: P. Kosir, Institute of Biology, Research Centre of the Slovenian Academy of Sciences and Arts, Novi trg 2, PB. 306, SI-1001 Ljubljana, Slovenia. Tel: +386 1 470 63 37. Fax: +386 1 425 99 97. Email: PetraKo@zrc-sazu.si ©2013 Societa Botanica Italiana Oak-hornbeam forests in SE Europe 85 within the order Fagetalia sylvaticae. These communities are very rich in species and are characterized by numerous relict and endemic species that survived Quaternary glaciations in southern European refugia (Trinajstic 1992, Bennett et al. 1991; Tzedakis 1993; Magri 1998; Petit et al. 2002). Some of these woods have been considered and recorded as old-growth forests (Blasi et al. 2010; Diaci et al. 2010; Horvath et al. 2012). There have been some synthetic reviews with attempts at establishing different vegetation types of oak-hornbeam forests in southeastern Europe, but on smaller areas (Biondi et al. 2002, 2008) or without numerical analyses (Marincek & Carni 2000) and in different taxonomic contexts (Ubaldi 2003). Numerous researches into forest vegetation in the Apennines and Balkans have been carried out, such as researches on beech forests (Dzwonko & Loster 2000; Bergmeier & Dimopoulos 2001; Di Pietro et al. 2004; Tzonev et al. 2006; Tsiripidis et al. 2007), broad-leaved ravine forests (Biondi et al. 2008; Kosir et al. 2008) and thermophilous deciduous forests (Blasi et al. 2004; Carni et al. 2009), in order to establish the major gradients of floristic differentiation of different forest vegetation types in the area. In these investigations, many similarities between the vegetation on both sides of the Adriatic Sea have also been established. In that respect, the question of Apennine and Balkan oak-hornbeam forests and the gradients of their floristic differentiation in the area is raised. The aim of the study was to establish the main types of oak-hornbeam (Carpinus betulus and Quercus sp. div) forests on the Apennines, Balkan peninsula and southern Alps and their correlations with ecological and phytogeographical gradients in the region, and to compare them with the major vegetation types recognized in the traditional expert-based classification in order to propose a synsystematic classification of the elaborated groups. Materials and methods Study area Oak-hornbeam forests were studied in the area of the Apennines, Balkan peninsula and southern Alps. The area is of very complex structure, since it comprises a part of the Pannonian basin, Padanian basin, the coasts of the Mediterranean Sea, southern hillsides of the Alps, the Apennines and various mountain chains in the Balkans. The research territory is classified into the Euro-Siberian region, above all into the Apennine-Balkan province and also into some adjacent areas of Pannonian-Carpathian provinces, the Adriatic province and Italo-Thyrrhenian province (Rivas-Marti-nez & Rivas-Saenz 1996-2009). Object of the research The objects of the research were oak-hornbeam forests from the area of the Apennines, Balkan peninsula and southern Alps. The stands are composed mainly of hornbeam (C. betulus), and frequently these forests are mixed with other species such as Q. petraea and Q. robur. In the Apennines and Balkan peninsula, in the stands Quercus cerris also appears and sometimes dominates because of forest management. This kind of wood occupies meso- to eutrophic sites, mostly shaded and moderate dry to moist. These stands differ from poor stands of alliance Quercion robori-petraeae and from moist and overflowed forests of the alliance Alnion incanae (Oberdorfer 1992). Methods Forest vegetation relevés made by applying the Braun-Blanquet (1964) approach, classified by their authors into alliances: Erythronio-Carpinion, C. moe-siacum, Physospermo verticillati-Quercion cerris, were collected from the literature, in addition to new and unpublished data. Methodological developments regarding conceptual aspects in accordance with the present state of phytosociology were taken into consideration (Biondi 2011; Biondi et al. 2011; Blasi et al. 2011; Blasi & Frondoni 2011; Feoli et al. 2011; Géhu 2011; Pott 2011; Schaminée et al. 2011). The relevés with an incomplete list of herb species indicated by the authors were not included into the analyses. We excluded the relevés whose dominant tree species (cover value 4 and 5) are species of other forest types, above all broad-leaved ravine, hygro-philous, coniferous and other climatozonal forests of the area (Abies alba, Acer platanoides, A. pseudoplata-nus, Alnus glutinosa, A. incana, Carpinus orientalis, Fagus sylvatica, Fraxinus angustifolia, F. excelsior, F. ornus, Ostrya carpinifolia, Picea abies, Pinus sp. div., Quercus frainetto, Q. ilex, Q. pubescens, Salix sp.div, Tiliaplatyphyllos, Ulmus glabra), as well as those where none of the tree species characteristic of oak-hornbeam forests (C. betulus, Q. cerris, Q. petraea, Q. robur) had a cover value of at least 2 (Chytrý et al. 2002; Košir et al. 2008). We did not include relevés without indication of altitude. As the distinction between these forests and forests of the alliance Alnion incanae and the order Quercetalia robori petraeae is sometimes difficult, above all due to similar dominant species, we calculated Pignatti indicator values (Pignatti et al. 2005) for each relevé, so relevés with extreme values of moisture and soil reaction (only when Quercus sp.div. dominated the stand) were excluded. Altogether, 1612 relevés collected from the literature and new ones were entered into the TURBO-VEG (Hennekens & Schaminée 2001) database. After exclusion of the relevés which did not meet the 86 P. Košir et al. criteria mentioned above, 1152 relevés remained. This data set was then stratified. Stratified resampling was made by combining the geographical stratification with stratification by phytosociological association (Rnollová et al. 2005). This means that up to 10 relevés of one association in one area were selected in such a way that different authors, different publications and different locations within the area were represented. We took the biogeo-graphic map of Europe (Rivas-Martinez & Rivas-Saenz 1996-2009) as the basis for geographical strata. The associations were defined according to expert assignments, and large associations were distinguished on the level of subassociations. After stratification 508 relevés remained. As many authors did not record mosses, we excluded them from our analysis before numerical processing. For the purpose of numerical analysis, we unified the system of layer division, which differs from author to author in the synoptic table. All layers were merged together into one. The numerical classification of the vegetation relevés, based on their species composition, was performed with TWINSPAN (Hill 1979), using its modified version available in the JUICE program (Tichý 2002). While the classical TWINSPAN algorithm divides each cluster coming from the previous division step, the modified algorithm divides only the most heterogeneous cluster in each step. Modification combines the classical TWIN-SPAN algorithm with the analysis of heterogeneity of the clusters prior to each division (Roleček et al. 2009). In such a way, we received successive partitions with 2, 3, 4, 5, etc., clusters, and of these we accept the partition which was effectively inter-pretable in phytogeographical and ecological terms, based also on authors' suggestions from the literature. Whittaker's beta was used as the heterogeneity measure. TWINSPAN pseudospecies cut levels for species abundance were set to 0-2-5-10-20% scale units as proposed by McCune and Grace (2002). Diagnostic species of each of the eight subclusters and four clusters were determined in the JUICE program (Tichý 2002) by calculating the fidelity of each species to each cluster and subcluster (Bruel-heide 1995, 2000; Chytrý et al. 2002), using the phi-coeficient. In these calculations, each group of relevés was compared with the rest of the relevés in the data set, which were taken as a single undivided group. Each of the eight subclusters and four clusters was virtually adjusted to 1/8 or 1/4 of the size of the entire data set, while holding the percentage occurrences of a species within and outside a target group the same as in the original data set (Tichý & Chytrý 2006). Species with phi > 30 were considered as diagnostic for individual subclusters and clusters, but species whose occurrence concentration in the relevés of a particular cluster or subcluster was not significant at P < 0.001 (Fisher's exact test) were excluded. Within the table, species were ordered by decreasing fidelity to individual clusters, i.e. by their decreasing diagnostic value. Since the diagnostic species are calculated on the basis of a data set of oak-hornbeam forests of southeastern Europe, they are only used for the purpose of differentiating the stands within these kinds of forests (Knollová & Chytrý 2004). Species in tree layer that appear in at least 50% of relevés of an individual cluster and subcluster are treated as constant. For further interpretation of the eight subclusters, unweighted average indicator values for relevés of the eight subclusters (Pignatti et al. 2005) calculated in the JUICE program and altitude values were presented with Box-whiskers diagrams made in the STATISTICA program (STATSOFT inc. 2007). Unweighted average indicator values and average altitude values for relevé subclusters were also passively projected onto a Principal Components Analysis biplot (PCA from CANOCO 4.5; Ter Braak & Smilauer 2002) to show ecological relationships among these subclusters and to explain environmental gradients underlying the main ordination axes. Square-root transformed percentage frequencies were used as the input data. We also calculated the spectra of geo-elements of individual subclusters. Spectra of geo-elements were calculated according to Pignatti et al. (2005). In general, the categories of geo-elements proposed by Pignatti et al. (2005) were taken into consideration, but some adjustments were made, such as Apennine endemic, Stenomediterranean, Eurymediterranean, Mediterranean-montane (incorporating montane S European), Eurasian, separately elaborating SE European (incorporating montane SE European) and Pontic, Atlantic (incorporating montane SW-European), Eurosiberian and Cosmopolite (incorporating Paleotropic and Adventive, Cultivated). In the calculations, we considered only species occuring in at least three relevés within an individual subcluster (Dzwonko et al. 1999; Košir et al. 2008). The spectra of geo-elements are presented as proportions (percentage) of the entire species composition of individual subclusters and indicated at the head of the synoptic table to show horological features of the subclusters. The nomenclature is according to Flora Europaea (Tutin et al. 1964-1980), except Acer neapolitanum Ten., Festuca exaltata C. Presl. and Pulmonaria apennina Cristof. & Puppi. Fagus moesiaca (K. Malý) Czeczott has been considered as Fagus sylvatica L. subsp. moesiaca (K. Malý) Szafer and therefore merged with F. sylvatica L. subsp. sylvatica into taxon F. sylvatica L. (Gomory et al. 1999). The taxon Oak-hornbeam forests in SE Europe 87 Quercus virgiliana (Ten.) Ten. is treated as Quercus pubescens s.l. (Skvorc et al. 2005). Results Clusters and their interpretation Figure 2 shows the result of the TWINSPAN classification of the data set, revealing eight groups of releves that are ecologically and phytogeographi-cally interpretable. In the first division of the TWINSPAN classification, Apennine forests (clusters 1 and 2) were separated from the Balkan and southern Alps forests (clusters 3 and 4). Apennine forests were further divided into two clusters; south Apennine forests (cluster 1) and northern-central and central Apennine forests (cluster 2). The Balkan and southern Alps forests were divided into two clusters; central-south Balkan forests (cluster 3), further divided into three subclusters according to their phytogeographical position (3.1 -lowland pannonian, 3.2 - hilly pannonian and 3.3 -montane central-south Balkan forests), and northwest Balkan forests (cluster 4), further divided into three subclusters according to ecology and phyto-geography (4.1 - azonal moist Quercus robur forests, 4.2 - submediterranean and prealpine basiphilous forests and 4.3 - subpannonian and predinaric moderate acidophylous forests). Cluster 1. This corresponds to subcluster 1.1 and is represented exclusively by oak-hornbeam forests from the southern Apennines (Figure 1; sectors 21a, 20d). They are moderatly acidophilous, thriving on the warmest and driest sites (Figure 3). Constant species in the tree layer are: C. betulus, Q cerris, A. neapolitanum and Sorbus torminalis. These forests correspond to the alliance Physospermo verticillati-Quercion cerris (Biondi et al. 2008). The cluster is characterized by species indicating the phytogeographical position of the releves in the south of the Apennines (Doronicum orientale, Anemone apennina, A. neapolitanum, F. exaltata, Physospermum verticillatum, Lathyrus niger subsp. jordanii, Viola odorata, etc.) and also by mesophilous elements of the submontane belt that are widespread in all of the southern area (Anthriscus nemorosa, Corydalis cava, Ilex aquifolium, Scilla bifolia, Arum orientale subsp. luca-num) and thermophilous species (Asparagus acutifo-lius, Erica arborea, Ruscus aculeatus, Quercus ilex, Rosa sempervirens) showing that these forests are in contact with evergreen forests of Quercetea ilicis. Cluster 2. This corresponds to subcluster 2.1 and is represented by releves from the northern-central and central Apennines (Figure 1; sector 9a). They thrive at highest altitudes with an average altitude value of 850 m and on sites with the highest indicator value of light (Figure 3). Constant species in the tree layer are Quercus cerris, Acer campestre and C. betulus. They were traditionally classified into the suballiance Pulmonario apenninae-Carpinenion betuli of the alliance Erythronio-Carpinion (Biondi et al. 2002, 2006, 2010). Both clusters (clusters 1 and 2) are represented by mesophilous forests dominated by C. betulus or Q cerris that thrive on the Apennines from the northern-central part to the south. These forests are often remnants of ancient wide forests and worthy of preservation according to Directive 92/43/EEC (European Commission 2007, Biondi et al. 2009). Unfortunately, they are dispersed in highly degraded areas and for this reason it is necessary to create ecological corridors that integrate, according to the Pan European Landscape Strategy (Council of Europe 1996), the areas with the greatest concentration of habitats sensu Directive 92/43/EEC as proposed in Biondi et al. (2012). Diagnostic species common for both clusters that comprise releves from the Apennines are indicated in Table I: Daphne laureola, Pulmonaria apennina, Viola alba subsp. dehnhardtii, Q cerris and Lilium bulbifer-um subsp. croceum. In comparison to the forests of the Balkan peninsula, the amount of Mediterranean species is higher in the Apennine forests, while the participation of Eurasian and SE-European species is lower. There are also some endemic species in the Apennine forests that separate these forests from the forests of the Balkan peninsula. Cluster 3. This is represented by central-south Balkan forests (Figure 1; sectors 9c-southeastern part, 10a). They have the most continental character (Figure 3), as is also indicated by diagnostic species (Table I) such as Acer tataricum and Tilia tomentosa (both pontic species). Constant species in the tree layer are C. betulus, A. campestre, and Q petraea. These forests were traditionally classified in the suballiance Lonicero-Carpinenion of the alliance Erythronio-Carpinion and in the alliance C. moesiacum. The proportion of Mediterranean-montane species is considerably lower in this cluster in comparison with all other clusters (Table I) and the proportion of pontic species is higher, which is all in accordance with the geographical position of the releves. Except for subcluster 3.1, the proportion of SE- European species is also relatively high. Subcluster 3.1. This is exclusively represented by forests from the pannonian sector of the Pannonian-Carpathian provinces close to the Illyrian sector (Figure 1; sector 10a; eastern Slavonia, Mecsek, Vrsacke planine, Sumadija), as is also indicated by 88 P.KoHretal. g Figure 1. The study area on the Biogeographical map of Europe (Rivas-Martinez & Rivas-Saenz 1996-2009) with the location of releves, included in the analyses. ^ Legend: The Apennine-Balkan province (9; shaded) with the Apennine (9a), Padanian (9b), Illyrian (9c), Pindan (9d) sectors, Alpine Q province (8) with Eastern Alpine sector (8d), Pannonian-Carpathian province (10) with the Pannonian sector (10a), Adriatic province (21) with the Apulian sector (21a) and Italo-Thyrrhenian province (20) with the Coastal west Italian sector (20d). Oak-hornbeam forests recognized in this paper: alliance: Physospermo verticillati-Quercion cerris | Physospermo verticillati- Quercenion cerris (Subcluster 1.1 in Table 1), | Pulmonario apenninae-Carpinenion betuli (Subcluster 2.1 in Table 1), alliance: Erythronio-Carpinion: O Aceri tatarici-Carpinenion betidi (Subcluster 3.1 in Table 1), • Aceri tatarici-Carpinenion betuli (Subcluster 3.2 in Table 1), ♦ Aceri tatarici-Carpinenion betuli (Subcluster 3.3 in Table 1), B Lonicero-Carpinenion betuli (Subcluster 4.1 in Table 1), o Lonicero-Carpinenion betuli (Subcluster 4.2 in Table 1), Lonicero-Carpinenion betuli (Subcluster 4.3 in Table 1). the lower proportion of SE-European species in comparison with the other two subclusters of this cluster. They are the most thermophilous and the most continental, thriving at low altitudes around 250 m (Figure 3). Constant species in the tree layer are C. betulus, Q. petraea, and T. tomentosa. The subcluster is characterized by a group of thermophilous and nitrophilous species with Oak-hornbeam forests in SE Europe 89 4.8 4.6 4 2 4.0 (b) — Mean I I Mean+SE T Mean+SD Ed 1.1 2.1 3.1 3.2 3.3 4.1 4.2 4.3 Subcluster 5.6 5.4 52 a 5.0 0 4.8 46 4.4 4.2 (c) 7.2 7.0 6.8 6.6 1 6.4 1 62 if) 6.0 5.8 5.6 5.4 (e) — Mean I I MeantSE ~T MeaniSD 1.1 2.1 31 3.2 3.3 4.1 Subcluster — Mean -j- □ Mean+SE T" Mean+SD B E3 1 1 2 1 3 1 3.2 3 3 4 1 42 4.3 Subcluster 58 56 50 48 46 (d) 6.4 a 5-8 I 5.6 5.0 (f) B — Mean I I Mean+SE ZL Mean+SD E3 B ^ B 1.1 2.1 3.1 3.2 3.3 4.1 4.2 4.3 Subcluster — Mean I I Mean±SE *T* Mean+SD 1.1 2.1 3.1 3.2 3.3 4.1 4.2 4.3 Subcluster Figure 3. Relationships of the eight main forest types of the Apennines, Balkan peninsula and southern Alps to Pignatti indicator values (a-f) and altitude (g). Boxes represent mean and standard errors (SE), whiskers indicate standard deviations (SD). Subclusters are numbered as in Figure 2. Oak-hornbeam forests in SE Europe 91 1200 1000 800 600 400 200 — Mean I I Mean+SE T Mean+SD (g) 2.1 3.1 3.2 3.3 Subcluster 4.1 4.2 4.3 Figure 3. (Continued) Subcluster 4.2. This represents the basiphilous zonal forests of the western part (pre-Alpine and submediterranean) of the northwest Illyrian sector, including also forests of the Padanian and Eastern-Alpine sector (Figure 1; sectors 9c, 9b, 8d). These forests thrive on shallow soils over carbonate bedrock (predominantly limestone) rich in nutrients; they are the most basiphilous ones (Figure 3). This subcluster is characterized by numerous Illyrian species. Diagnostic species (Table I, e.g. Anemone trifolia, Carex alba, C. purpurascens, H. epipactis, L. orvala, Mercurialis perennis, Omphalodes vema) indicate the geographical position in the pre-Alpine and submediterranean area of the northwest Balkans and the basiphilous character of the stands. Constant species in the tree layer are C. betulus and Acer campestre. Subcluster 4.3. This is represented by neutrophilous and moderate acidophilous forests predominantly of the eastern part (pre-Dinaric, subpannonian) of the northwest Illyrian sector (Figure 1; sector 9c) which thrive on deeper soils poor in carbonate; on sandstones, clay, loam or non-calcareous flysch, and also on deeper soils over carbonate bedrock. The subcluster is characterized by moderate acidophilous species such as Gentiana asclepiadea, Castanea sativa, Luzula luzuloides, Serra-tula tinctoria, Hieracium racemosum and others (Table I). Constant species in the tree layer are C. betulus, Q. petraea agg, and F. sylvatica. Indicator values and altitude value The PCA is presented of the eight subclusters of oak-hornbeam forests of the research area with mean Pignatti indicator values and altitude plotted as supplementary variables on the ordination diagram (Figure 4). Eigenvalues of the first two axes are 0.377 and 0.172. Oak-hornbeam forests of the research area are separated along axis 1 according to phytogeography, similarly as in the TWINSPAN classification (Figure 2; four compartments corresponding to four clusters in the TWINSPAN classification). The underlying ecological gradients of axis 1 are temperature, altitude, moisture, light and nutrient, which all reflect different climates of the different phytogeographical regions. Along axis 2, forests are separated according to altitude and soil reaction (Figure 4). Continentality is only correlated with axis 3 and therefore not shown on the PCA diagram. Discussion Gradients and classification The TWINSPAN classification reflects both the ecological and phytogeographical gradients that are sometimes difficult to separate as the differences in geographical position that result from different macroclimatic and geological conditions are always reflected together with ecological ones. The first division separates the Apennine forests from the Balkan and southern Alps forests. The vegetations of the Apennines and Balkans share a part of their history and therefore similar species composition, but there are also differences in species composition between both peninsulas because of the different climate and therefore ecology of these forests. The first four groups (second level of division) correspond to the main phytogeographical groups: (1) southern Apennines, (2) northern-central and central Apennines, (3) central-southern Balkans and (4) north-western Balkans and southern Alps. 92 P. Kosir et al. Table I. Synoptic table of species occurrence (percentage frequency) in the eight main forest types of oak-hornbeam forests in southeastern Europe resulting from the TWINSPAN classification (see also Supplementary material). Subcluster number 1.1 2.1 3.1 3.2 3.3 4.1 4.2 4.3 No. of releves Cluster number Proportion of geo-elements in clusters (%) Apennine endemic Stenomediterranean Eurymediterranean Mediterranean-montane Pontic Eurasian SE-European Eurosiberian Atlantic Cosmopolite Species diagnostic for one cluster Cluster 1 Doronicum Orientale Anemone apennina Acer neapolitanum Ilex aquifolium Festuca exaltata Teucrium scordonia subsp. euganeum Allium pendulinum Ruscus aculeatus Cyclamen hederifolium Physospermum verticillatum Cyclamen repandum Carex hallerana Erica arborea Lathyrus niger subsp. \ordanii Quercus ilex Viola odorata Sorbus domestica Cytisus villosus Ranunculus lanuginosus Rosa sempervirens Scilla bifolia Arum italicum Poa trivialis Buglossoides purpurocaerulea Tamus communis Rubus caesius Crepis leontodontoides Rubia peregrina Asphodelus aestivus Anthriscus nemorosa Geranium sanguineum Potentilla micrantha Sorbus torminalis Sanicula europaea Rosa canina Bellis sylvestris Arum Orientale subsp. \ucanum Cluster 2 Acer obtusatum Festuca heterophylla Rosa arvensis Geranium nodosum Luzula forsteri Juniperus communis Dactylorhiza fuchsii Lathyrus venetus Helleborus bocconei 33 1 42 33 30 45 93 2 12 6 1 10 26 4 1 I 9 II 10 20 64 3 62 43 57 4 65 91 0.61 0.52 12? 345 1.23 1.52 1.76 1.05 0.99 13.93 8.37 7.36 7.58 5.88 5.37 3.66 5.45 4.1 4.93 2.45 1.52 2.94 4.1 3.85 5.24 5.94 44.26 47.78 56.44 58.33 51.76 58.46 51.83 53.47 3.28 4.43 3.68 ^32 7.85 6.93 7.38 12.81 13.5 10.61 13.53 17.8 18.32 2.46 3.94 2.35 2.62 2.46 3.94 4.29 4.55 2.94 5.38 4.71 2.97 52 14 22 23 24 7 19 9 40 35 7 16 5 30 14 28 14 20 29 15 10 13 15 6 6 _ 7 _ 18 3 3 - - - - - - O 9 5 _ 21 _ 3 _ 37 16 18 9 7 8 21 28 6 2 - 21 22 3 29 3 29 7 9 - 14 19 8 39 42 2 6 31 44 16 29 56 33 17 53 12 3 8 12 - - 1 19 36 {continued) Oak-hornbeam forests in SE Europe 93 Table I. (Continued Subcluster number 1.1 2.1 3.1 3.2 3.3 4.1 4.2 4.3 Lonicera caprifolium 3 56* 17 13 23 5 15 27 Melica uniflora 64 70* 34 42 44 16 6 13 Euonymus latifolius - 22* - - 5 - 2 1 r Primula vulgaris - 73 23 13 51 5 83* 40 Prunus spinosa 27 39 14 5 23 7 2 5 Platanthera chlorantha - 14* - - - - - - Bromus ramosus agg. 9 24* 11 - - - 2 1 Digitalis lutea subsp. australis 12 15 - - - - - - Crataegus laevigata - 49 27 5 5 44 22 18 Astragalus glycyphyllos 6 23 3 2 14 - 3 1 Lonicera xylosteum 9 38 - 11 7 - 42 7 Cluster 3 Helleborus odorus Tilia tomentosa Acer tataricum Glechoma hirsuta Cluster 4 Coronilla elegans Hieracium praealtum subsp. bauhinii Chamaespartium sagittale Vicia cracca 22 Anemone nemorosa - 13 8 2 21 65 65 Aposeris foetida - - - - 14 ? 51* Cyclamen purpurascens - - - 3 5 51* Crocus vernus 6 1 - - 5 19 45* Gentiana asclepiadea - - - - 5 25 3 Luzula pilosa - - - 10 9 47* 17 Lamium orvala - - - 2 5 7 46* Oxalis acetosella - - 5 16 5 58* 35 Vinca minor - 3 5 5 7 16 62* Athyrium filix-femina - - 6 19 5 72* 11 Daphne mezereum - - - - 7 11 22 Picea abies - - - - 2 12 31* Hacquetia epipactis - - - 2 - - 42* Euphorbia dulcis - 35 - 6 12 42 45 Maianthemum bifolium - - - 2 - 32* 8 Robinia pseudacacia - - 2 3 2 4 40* Knautia drymeia - 8 2 13 9 12 29 Carex digitata 15 3 2 5 12 5 52* Carex brizoides - - 2 5 - 54* - Lamiastrum galeobdolon - 6 31 35 12 70* 48 Species diagnostic for more than one cluster Daphne laureola 70* 66* - - 16 - 2 Pulmonaria apennina 1% - - - - - Viola alba subsp. denhardtii 39* - - - - - Quercus cerris 85* 52 24 30 2 15 Lilium bulbiferum subsp. Croceum 33* 30* - - - - 3 Species diagnostic for one subcluster Asparagus acutifolius 12* 1 - - - - - Cardamine graeca 12* 1 - - - - - Lamium maculatum 12 - 44* 3 5 7 - Galium aparine 15 9 50* 5 2 4 2 Alliaria officinalis 12 2 41* 3 - 2 6 Dactylis glomerata subsp. aschersoniana - 1 23* - 2 2 2 Veronica hederifolia 18 - 22* - - - - Geranium robertianum 9 27 48* 11 9 4 11 Stachys sylvatica 3 3 27* 5 2 2 5 Ranunculus ficaria 39 1 48* 2 2 25 18 Ranunculus cassubicus s.lat. - - 11* - - - - Quercus frainetto 3 - 14* - 2 - - Rosa species - - 9 26* 7 2 6 Lathyrus vernus - 9 22 63* 21 18 40 Ruscus hypoglossum - 2 9 29* - 4 - 59* 34 29 46* 41 26 26 25 34 32* 18 16 56 13 14 47* 30 8 35 1 10 4 3 1 1 2 14 31 11 16* (continued) 94 E Kohr et al. Table I. (Continued Subcluster number 1.1 2.1 3.1 3.2 3.3 4.1 4.2 4.3 Danthonia decumbens - - - - 14* - - - Physospermum cornubiense - 2 - - 19* - 5 - Pyrus pyraster 3 32 16 19 z 18 8 32 Potentilla erecta - - - - - - 4 Quercus robur - 4 28 15 9 89* 18 10 Galeopsis tetrahit - 3 9 8 2 49* - 3 Pseudostellaria europaea - - - - - 19* - 1 Gagea spathacea - - - - - 16* - - Circaea lutetiana - 4 16 31 - 51* 2 13 Veronica montana 18 3 9 8 - 30* - 1 Scrophularia nodosa - 2 8 11 5 39* 3 21 Carex remota - 1 8 - - 19* - 1 Anemone trifolia - 19 - 3 5 - 54* 3 Carex alba - - - 2 - - 23* - Fraxinus excelsior - 5 8 2 9 2 40* 3 Omphalodes Verna - - - - 2 - 25* 3 Colchicum autumnale - - - - - - 20* 2 Hepatica nobilis - 44 12 16 12 - 62* 10 Asplenium scolopendrium 6 - - - 2 - - Lathraea squamaria - - 5 - - 4 26* 7 Salvia glutinosa - 25 - 6 14 - 51* 25 Melica nutans - - 6 2 5 2 34* 18 r Primula vulgaris - 73 23 13 51 5 83* 40 Helleborus viridis - - - 2 - 2 15* - Galanthus nivalis 24 8 27 3 7 5 10 Mercurialis perennis 18 6 25 6 21 7 48* 10 Asarum europaeum - 16 27 48 33 26 78* 58 Helleborus multifidus subsp. istriacus - - - - - - 11* - Luzula luzuloides - - - 5 19 9 2 35* Castanea sativa 12 12 - 3 14 11 20 51* Serratula tinctoria - 9 - 2 7 2 9 35* Hieracium racemosum 6 4 - 3 2 9 3 32* Quercus petraea agg. 3 15 61 85 84 23 51 96* Molinia arundinacea - - - - - - - 11* Convallaria majalis - - 8 3 9 7 12 32* Solidago virgaurea - 22 - - 14 5 18 42* Species diagnostic for more than one subclusters Corydalis cava 36* - 31* - - 2 12 4 Pteridium aquilinum 67* 35 - 10 33 11 5 63* Other species with high frequency Carpinus betulus 76 80 100 97 100 100 100 99 Acer campestre 64 82 86 79 72 47 86 44 Viola reichenbachiana 61 71 48 42 70 51 60 63 Crataegus monogyna 76 61 66 56 70 26 55 41 Hedera helix 88 77 53 47 33 21 69 58 Corylus avellana - 63 16 39 72 58 85 75 Fagus sylvatica 33 48 25 79 56 46 31 68 Rubus fruticosus agg. 55 41 27 85 28 53 17 66 Pulmonaria officinalis - 8 55 47 74 44 78 59 Fragaria vesca 58 60 38 24 67 30 28 52 Prunus avium 3 30 45 68 51 32 45 74 Euphorbia amygdaloides ■58 44 48 52 70 23 20 15 Polygonatum multiflorum 36 17 34 37 16 63 55 56 Cornus sanguinea 3 45 34 56 35 30 58 43 Carex sylvatica 45 33 23 39 21 61 22 57 Brachypodium sylvaticum 58 44 30 16 49 19 45 35 Fraxinus ornus 24 45 41 52 51 - 40 37 Stellaria holostea 9 12 41 60 53 46 11 48 Geiun urbanum 61 45 59 31 33 21 11 3 Euonymus europaeus 36 34 34 26 12 33 51 32 Symphytum tuberosum - 16 17 21 53 33 69 46 Galium odoratum 36 15 27 47 23 49 6 47 Ajuga reptans 3 34 41 29 35 56 11 38 (continued) Oak-hornbeam forests in SE Europe 95 Table I. (Continued Subcluster number 1.1 2.1 3.1 3.2 3.3 4.1 4.2 4.3 Ligustrum vulgare 18 33 38 42 30 11 35 34 Galium sylvaticum agg. 3 8 23 50 49 21 35 51 Cruciata glabra 3 52 3 34 37 25 22 57 Mycelis muralis 24 38 16 44 28 35 12 32 Acer pseudoplatanus - 27 9 21 40 12 58 52 Cardamine bulbifera 27 25 34 15 21 35 26 29 Carex pilosa - - 38 44 28 23 14 30 Aremonia agrimonoides 39 42 14 21 44 - 5 8 Campanula trachelium 21 38 11 8 37 2 32 23 Aegopodium podagraria 6 22 20 6 21 26 49 19 Cornus mas 3 32 36 29 30 4 25 7 Dryopteris filix-mas 6 1 9 24 21 44 34 27 Clematis vitalba 27 41 12 15 19 - 28 9 Veronica chamaedrys 3 22 20 11 47 19 3 18 Melittis melissophyllum - 22 11 27 33 - 15 18 Tilia cor data - 2 11 18 9 25 37 15 Dactylis glomerata 12 22 14 26 30 2 3 3 Milium effusum 27 8 12 11 5 23 2 23 Tilia platyphyllos 12 9 12 21 23 4 20 10 Ulmus glabra 3 6 20 26 7 2 31 12 Hieracium murorum 15 26 - 2 12 16 5 29 Sambucus nigra 3 2 27 24 2 16 20 8 Note: Diagnostic species for the clusters and subclusters (defined as those with phi > 30) are shown, ranked by decreasing value of the phi-coefficient, indicated by shadings (for clusters and subclusters) and asterisks (for subclusters). CO O CO O Temperature Soil Reaction Light Altitude -1.0 1.0 Figure 4. Passive projection of Pignatti indicator values and values of altitude onto the PCA diagram of eight subclusters. The subclusters are numbered as in Table I and Figure 2. Only indicator values with the highest correlations with the first two PCA axes are shown. The highest correlations with the first axis have the indicator values for temperature (0.7053), altitude (0.6641), moisture ( — 0.6198), light (0.6104) and nutrient ( — 0.5780), with the second axis the values for altitude ( — 0.6236) and soil reaction ( — 0.5444). The main gradient that influences species composition in oak-hornbeam forests on the Apennines is the macroclimatic gradient north-south. Gradients on the Balkan peninsula are more complex. Besides the macroclimatic gradient north-south (northwest to southeast), continental-ity is also very important and also the presence of the mountain chains of the Alps and Balkans. Therefore oak-hornbeam forests on the Balkans are more diverse and both Balkan groups (clusters) are further divided into three subgroups (subclusters) . We cannot find such a diversity in the Italian peninsula because it is very narrow and the con-tinentality is evident only in a few mountain areas that are more complex in morphology, such as in the central Apennine areas (from the mountain chain of Sibillini to Gran Sasso). 96 P. Kosir et al. Oak-hornbeam forests in the northwest Balkans are zonal vegetation, therefore the ecological diversity of these forests is higher than that towards the south of the Balkans, where this vegetation is azonal, and all diversity is due only to gradients of continentality and altitude. The northwestern Balkan and southern Alps forests are further divided by the TWINSPAN into three ecological groups: moist Q. robur group, basiphilous and moderate acidophilous group, while central-southern Balkan oak-hornbeam forests are separated into three phytogeographical groups: lowland panno-nian, hilly pannonian and montane south-central Balkan. In the northwest Balkans, in a more humid and cold climate, some Q. robur forests are classified as oak-hornbeam forests and are transitional towards the alliance Alnion incanae. Towards the south, because of the warmer and less humid climate, Q. robur forests develop only on very moist and overflowed soils and are therefore classified within alliance Alnion incanae. Towards the south of the Balkans, where this type of vegetation is azonal, due to the warmer climate forests thrive on colder, acidic soils, at higher altitudes and also in shaded, moist and cold valleys at lower altitudes in the zone of Q. frainetto forests (Kojic et al. 1998). In the Apennines, this type of vegetation extends far to the south of the peninsula (also including the Gargano peninsula), while in the Balkans only to the region of Macedonia, and there is no indication of the appearance of Carpinus forests in Greece (Raus 1980; Bergmeier 1990). The main reason is probably the different macroclimatic circumstances of the two peninsulas. The climate of the Apennines is - in comparison to the southern part of the Balkans -more oceanic or suboceanic with a higher amount of precipitation (Blasi et al. 2004), that enables the development of mesophilous oak-hornbeam forests also at lower altitudes, despite their geographical position in the south. The lack of similarity between the Apennine and Balkan clusters, as indicated by the dendrogram and by the high number of differential species and lack of common species (Table I) between the Apennine and the Balkan oak-hornbeam forests, suggests a revision of the syntaxonomic position of oak-hornbeam forests of the Apennines separately from Balkan, southern Alps and padanian oak-hornbeam forests. On the other hand, numerical analysis has revealed a high similarity between northern- central and southern Apennine oak-hornbeam forests (clusters 1 and 2), which were traditionally classified into two different alliances. This similarity is also confirmed by the group of diagnostic species common for both groups of forests (Table I). Therefore, the suballiance Pulmonario apenninae-Carpinenion betuli, traditionally classified into the alliance Erythronio-Carpinion, is now at our suggestion classified into the alliance Physospermo verticilla-ti-Quercion cerris that comprises together forests of Q. cerris and C. betulus of the Apennines. The typical suballiance Physospermo verticillati-Quercenion cerris suball. nova, corresponds to the formations of the southern Apennines, as described in Biondi et al. (2008), while the suballiance Pulmonario apenninae-Carpinenion betuli comprises the central and northern Apennines formations. In Table I the characteristic and differential species of the two suballiances are brought into evidence. Analyses support the classification of the northwestern and central-southern Balkan and southern Alps oak-hornbeam forests into the common alliance Erythronio-Carpinion. In this way, the classification of central-southern Balkan oak-hornbeam forests is solved, as these forests were traditionally classified into the provisonal alliance C. moesiacum. Both alliances, Balkan and southern Alps alliance Erythronio-Carpinion and Apennines alliance Physospermo verticillati-Quercion cerris, are vicariants to the Central-European alliance Carpi-nion betuli. This is not the same pattern as used for some other types of vegetation {Aremonio-Fagion, Ostryo-Tilienion), where forests of the Apennines and Balkans were classified into the same alliance or suballiance vicariant to the central European alliance or suballiance. The reason for the lack of similarity between the Apennine and Balkan oak-hornbeam forests - and therefore different classification of these forests - could lie in the fact that these forests in the research area are anthropozoi-cally favored and that they are thriving on sites where dominant forests of the region, such as F. sylvatica forests and thermophilous Q. cerris and Q. pubescens forests, cannot develop. These sites seem to be considerably different between both peninsulas. The traditionally phytogeographically defined sub-alliances Lonicero-Carpinenion betuli, Erythronio-Car-pinenion and Asparago tenuifolii-Carpinenion were not distinguished by numerical analysis, and were therefore joined together into one phytogeographically wider defined suballiance Lonicero-Carpinenion betuli comprising oak-hornbeam forests of the northwestern Balkan and southern Alps, within which the forests are divided ecologically into three groups. For the central-southern Balkan oak-hornbeam forests we propose a new suballiance Aceri tatarici-Carpinenion. Concerning all these facts and the numerical analyses carried out in this research, we propose the following syntaxonomy of the oak-hornbeam forests of southeastern Europe: Oak-hornbeam forests in SE Europe 97 Proposed syntaxonomic scheme Class: Querco-Fagetea Br.-Bl. et Vlieger in Vlieger 1937 Order: Fagetalia sylvaticae Pawlowski et al. 1928 Alliance: Physospermo verticillati-Quercion cerris Biondi et al. 2008 Suballiance: Physospermo verticillati- Quercenion cerris Biondi et Casavecchia in Kosir et al. suball. nova hoc loco (cluster 1 in Table I) Suballiance: Pulmonario apenninae-Carpinenion betuli Biondi et al. 2002 (cluster 2 in Table I) Alliance: Erythronio-Carpinion betuli (Horvath 1938) Marincek in Wallnofer, Mucina et Grass 1993 (clusters 2, 3 and 4 in Table I) Suballiance: Aceri tatarici-Carpinenion betuli Kosir et al. all nova hoc loco (cluster 3 in Table I) (incl. C. moesiacum) Group of lowland pannonian associations (subcluster 3.1 in Table I) Group of hilly pannonian associations (subcluster 3.2 in Table I) Group of montane central-south Balkan forests (subcluster 3.3 in Table I) Suballiance: Lonicero caprifoliae-Carpinenion betuli Vukelic in Marincek 1994 (cluster 4 in Table I) (incl. Asparago tenuifolii-Carpinenion betuli Marincek & Poldini 1994., Erythronio-Carpinenion betuli Marincek 1994) Group of Quercus robur associations (subcluster 4.1 in Table I) Group of basiphilous associations on carbonate bedrock in the pre-Alpine and submediterranean region (subcluster 4.2 in Table I) Group of neutrophilous-moderate acidophilous associations mostly on noncarbonate bedrock in pre-Dinaric and subpannonian region (subcluster 4.3 in Table I) The holotypus of the Physospermo verticillati-Querce-nion cerris is the association Physospermo verticillati-Quercetum cerris Aita et al. 1977 em Ubaldi et al. 1987 holotypus hoc loco. 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