PHYTOSOCIOLOGICAL DESCRIPTION OF QUERCUS PETRAEA FOREST STANDS WITH CHAMAECYTISUS HIRSUTUS AND ERICA CARNEA IN THE VIPAVSKA BRDA (SOUTHWESTERN SLOVENIA) FITOCENOLOŠKA OZNAKA SESTOJEV GRADNA (QUERCUS PETRAEA) Z DLAKAVO RELIKO (CHAMAECYTISUS HIRSUTUS) IN SPOMLADANSKO RESO (ERICA CARNEA) V VIPAVSKIH B

We conducted a phytosociological study of Quercus petraea stands, whose herb layer is dominated by Erica carnea in the flysch hills of Vipavska brda and on the margins of the Vrhe plateau (southwestern Slovenia). We have determined that they are a long-term degradation stage on beech forest sites from the association Seslerio autumnalis-Fagetum. Based on comparisons with similar sessile oak stands from associations Melampyro vulgati-Quercetum petraeae, Seslerio autumnalis-Quercetum petraeae and Erico carneaeQuercetum petraeae, the studied stands are classified into the new association Chamaecytiso hirsuti-Quercetum petraeae. They are best differentiated from the stands of compared communities by the species Erica carnea, Sorbus aria, Lathyrus linifolius, Loranthus europaeus and Erythronium dens-canis. The new association is classified into the alliance Carpinion orientalis and order Quercetalia pubescenti-petraeae.


INTRODUCTION UVOD
The forest of the Vipavska brda in southwestern Slovenia as seen from a distance (e.g. from the Nanos plateau) gives a fairly uniform picture. A closer view, however, shows that these are secondary stands that clearly demonstrate the impact of past management. In terms of ecology -these are steep, shady flysch slopes cross-cut with streams -the highest stage of development in the primary post-glacial development in this area was probably beech forest. Individual beech trees can still be found in numerous spots, as well as many beech stands, especially on higher elevations on slopes under the Vrhe plateau and in the eastern part of the hills towards Razdrto and Raša. We conducted a phytosociological inventory of several such beech stands that are mainly classified into the association Seslerio autumnalis-Fagetum (compare Dakskobler, 1997). The dominant species now is without a doubt sessile oak (Quercus petraea), and its stands, whose herb layer is dominated by autumn moor grass (Sesleria autumnalis), are classified into the association Seslerio autumnalis-Quercetum petraeae (Čarni et al., 2002). We were especially interested in low-growing oak coppice stands, where the herb layer is completely dominated by spring heath (Erica carnea). Elevation, geological bedrock, slope are similar as in beech or sessile oak stands with autumn moor grass, while the herb layer is clearly different. Degradation and, in turn, deterioration of soil-and consequently of site conditions and changes in the species composition could have been caused by erosion (removal of soil still ongoing in several locations) and definitely also by past human activities, especially by litter gathering (Čokelj, in litt.). A phytosociological inventory was conducted for both beech and oak stands; the relevés were arranged into two tables and the results of our research are presented in this paper.

Ecological description of the study area Ekološki opis raziskovanega območja
The name Vipavska brda denominates the hills situated south of the Vipava river, north of the Branica river and west of the Močilnik stream (Kladnik, 2000) in southwestern Slovenia. In the east, the hills gradually continue into the Vrhe plateau between the Vipava and Raša valleys. The shady slopes of the Vipavska brda and of the Vrhe plateau above the Močilnik and Pasji rep streams are now mainly covered with forests. Settlements are located both on the plateau and in the valley. Figure 1 shows the approximate location of inventoried sessile oak stands, whose herb layer is completely dominated by spring heath (Erica carnea). The elevation of the localities is between 290 m and 535 m, the aspect is distinctly shady, northern, northeastern, eastern as well as southeastern, the slope is 5° to 30°. Geological bedrock of the Vipavska brda is Eocene flysch (Buser, 1973(Buser, , 2009 and the predominant soil type is eutric brown soil (Lovrenčak, 1998, Prus, in litt.).
The climate is warm, with mean annual temperature of 10ºC to 12ºC (Cegnar, 1998) and mean annual precipitation of between 1,400 mm and 1,600 mm (B. Zupančič, 1998). The phytosociological map of potential natural forest vegetation of Slovenia, scale 1: 400,000 (Čarni et al., 2002), indicates the study area as the association Seslerio autumnalis-Quercetum petraeae. According to our findings, beech forest is the potential natural vegetation of shady slopes of the Vipavska brda, especially the forest from the association Seslerio autumnalis-Fagetum, in part also from the association Ornithogalo pyrenaici-Fagetum. Stands of the association Seslerio autumnlais-Quercetum petraeae (see relevés 11 and 12 in Table 2) in this area are largely secondary degradation stage. Although the steep flysch slopes have always been largely wooded, the military map from the second half of the 18th century (Rajšp and Trpin, 1997) indicates relatively large viticultural areas also on the shady slopes, at least in the Pasji rep  Table 2. Sites on what was once clearly agricultural land are increasingly overgrown by black locust (Robinia pseudoacacia).

MATERIALS AND METHODS MATERIALI IN METODE
Vegetation in the Vipavska brda was researched applying the Central-European phytosociological method (Braun-Blanquet, 1964). A total of 39 relevés were made and entered into the FloVegSi database (Seliškar et al., 2003). Combined cover-abundance values were transformed into numerical values 1-9 (van der Maarel, 1979). Numerical comparisons were conducted with the software package SYN-TAX (Podani, 2001). Relevés were arranged into two analytic tables (Tables 1 and 2) based on hierarchical classification. We integrated the results of the (unweighted) pair group method with arithmetic mean "(Unweighted) average linkage" -UPGMA, where Wishart's similarity ratio was applied. Phytosociological groups (= groups of diagnostic species) were formed on the basis of our own criteria, but with consideration of several authors (Aeschimann et al., 2004, Poldini, 1982, 1988, 1989, Zupančič, 1999. Similar oak communities from the sub-Mediterranean part of Slovenia (Poldini, 1982, Zupančič, 1999 and from serpentine areas in Bosnia (Krause andLudwig, 1957, Ritter-Studnička,1970) were compared through hierarchical classification and two-dimensional ordination (principal coordinates analysis, PCoA), as well as on the basis of Sørensen's coefficient of floristic similarity (Sørensen, 1948) and analysis of percentage of diagnostic species of syntaxonomic groups. The nomenclature source for the names of vascular plants is Mala flora Slovenije (Martinčič et al., 2007). Martinčič (2003Martinčič ( , 2011 is the nomenclature source for the names of mosses, Šilc and Čarni (2012) for the names of syntaxa (with the exception of the names of the class Querco-Fagetea Braun-Blanquet et Vlieger in Vlieger 1937 and alliance Carpinion orientalis Horvat 1958) and Urbančič et al. (2005) for the names of soil types.

Description of soils in the researched stands Opis tal v preučenih sestojih
Soil conditions were described on the basis of the sample that was obtained in the Pasji rep valley and analysed in the laboratory of the Slovenian Forestry Institute, as well as on the basis of the public data provided by the Infrastructural Centre for Pedology and Plant Protection at the Department of Agronomy of Biotechnical Faculty in Ljubljana, which were interpreted for us by Tomaž Prus (in litt.). Convex slopes with relatively shallow soil prevail, in places showing signs of erosion (leaching). The dominant soil type is lessivé eutric brown soil. Upper horizons are strongly acid (pH H 2 O 4.8, pH CaCl 3.8 to 4.0), the humus type is moder (C/N ratio exceeds 20). Soil properties change with depth and pH increases considerably. This indicates past practices on surface soil horizons. Litter gathering is one of the likely reasons that accelerated the process of soil base cation (Ca, Mg, K) leaching. Although characteristic for alkaline soils, Erica carnea can thrive also on soils that have gradually become acid. In the event of further soil degradation (acidification), it would be replaced by Calluna vulgaris, which has only been found in isolated spots in our relevés. Abundant occurrence of Erica carnea in the Vipavska brda can be attributed to the distinctly shady aspect, i.e. local climate factors, erosion-associated processes on convex slopes and to past litter gathering. (Table 1) 3.2 Oznaka sestojev in vrstna sestava (preglednica 1) Pole-and mature sessile oak stands prevail on 39 researched plots; their diameter at breast height is between 25 cm and 35 cm and tree height between 10 m and 16 m. Many of them are of coppice origin. Frequent occurrence of the parasite Loranthus europaeus in sessile oak crowns indicates relatively poor vitality of sessile oak on these sites. The upper tree layer is admixed with individual trees of Fagus sylvatica, Castanea sativa and Sorbus aria, very rarely also by Pinus nigra (subspontaneously), Betula pendula, Ostrya carpinifolia, Sorbus aucuparia and Pinus sylvestris. The alien species Robinia pseudoacacia was recorded in the tree layer on one of the plots. The species that frequently occur in the lower tree layer and in the upper shrub layer include Fraxinus ornus, Sorbus aria, S. torminalis, Juniperus communis, in places also Castanea sativa and Fagus sylvatica, and only rarely Laburnum alpinum, Pyrus pyraster, Amelanchier ovalis and Crategus monogyna. In the shrub layer, we inventoried the taxa Sorbus graeca and S. austriaca, but our determination is not completely reliable. Above Veliki graben above Otošče we found a rare hybrid between Sobus aria and S. torminalis = Sorbus latifolia s. lat. In addition to the dominating Erica carnea, the taxon Molinia caerulea subsp. arundinacea, in places also the species Convallaria majalis, Serratula tinctoria and Vaccinium myrtillus, on several spots also Pteridium aquilinum, have a higher medium coverage. Common grasses include Sesleria autumnalis, Avenella flexuosa and Calamagrostis arundinacea; Luzula luzuloides is also frequent. Species with high constancy (more than 50%) in the herb layer are also Chamaecytisus hirsutus, Tanacetum corymbosum, Hieracium racemosum, H. sabaudum, H. murorum, Genista pilosa, Platanthera bifolia and Erythronium dens-canis. Common species in the moss layer are Hypnum cupressiforme, Thuidium tamariscinum and Polytrichum formosum (= Polytrichastrum formosum), with Leucobryum glaucum observed on several plots. (Table 2) Table 2 comprises 13 relevés from the same area (Vipavska brda, Vrhe), but with a different composition of the tree layer. Ten relevés (1 to 10) are classified into the association Seslerio autumnalis-Fagetum, two are a degradation stage with dominant sessile oak on a beech site (relevés 11 and 12, both classified into the association Seslerio autumnalis-Quercetum petraeae). Relevé No. 13 characterises a pioneer forest on former agricultural land dominated by Prunus avium, with individual specimens of Ostrya carpinifolia, Acer pseudoplatanus, A. campestre and Robinia pseudoacacia. We assume this is a pioneer stage on potential sites of the association Ornithogalo pyrenaici-Fagetum. Comparison of 26 relevés of sessile oak forest with ten relevés of the beech forest from the association Seslerio autumnalis-Fagetum from the same area indicates substantial differences not only in the tree layer, but also in the herb layer. In beech stands, it is usually dominated by Sesleria autumnalis, there are clearly more mesophilous species, character species of the order Fagetalia sylvaticae (see Tables 2 and 4). The soil is deeper, less acid and in places also moister.

Synsystematic classification Sinsistematska opredelitev
Natural characteristics (flysch slopes), phytogeographical position and origin (secondary community) of the studied stands are similar to the conditions in which sessile oak stands of the syntaxon Melampyro vulgati-Quercetum petraeae var. geogr. Fraxinus ornus (Puncer andZupančič, 1979, Zupančič, 1994) grow in the hills of Brkini. We conducted a comparison between 19 relevés of this association and our relevés; floristic similarity according to Sørensen (1948) is about 56%, which allows for classification into the same association, but new subassociation Melampyro-Quercetum ericetosum carneae. Such classification is conditionally supported also by the presence of diagnostic species from the association Melampyro-Quercetum in the studied stands in the Vipavska brda. In addition to sessile oak, Luzula luzuloides, Hieracium sabaudum and the geographical differential species Avenella flexuosa (= Deschampsia flexuosa) also frequently occur in these stands. Melampyrum pratense subsp. vulgatum and Chamaecytisus supinus occur with considerably lower frequency and medium coverage, whereas Lembotropis nigricans and geographical differential species Orobanche nana (O. ramosa subsp. nana) were not recorded. There are obvious differences in the proportion of diagnostic species (Table 4). The studied stands comprise a considerably higher proportion of thermophilous species of the order Quercetalia pubescentipetraeae and class Erico-Pinetea and a much smaller proportion of acidophilous species of the order Quercetalia roboris and class Vaccinio-Piceetea than the stands of the association Melampyro-Quercetum. Soil conditions are different. Dystric brown soils prevail in the stands of the association Melampyro-Quercetum, whereas the soil in our stands is eutric, although frequently leached. The fundamental difference is in potentially natural vegetation. In terms of the association Melampyro-Quercetum, this is most frequently a moderate acidophilous beech-oak forest from the association Castaneo-Fagetum sylvaticae, in our case the sub-Mediterranean beech forest from the association Seslerio autumnalis-Fagetum. This is also the basis for classification into two different orders. The association Melampyro-Quercetum is classified into the alliance Quercion roboris (or Genisto germanicae-Quercion roboris) and into the order Quercetalia roboris, while the studied stands with their floristic composition are classified into the alliance Carpinion orientalis and into the order Quercetalia pubescenti-petraeae. If these stands were classified as the new subassociation Melampyro-Quercetum petraeae ericetosum carneae it should be classified into the same alliance as the previously described subassociations (Puncer and Zupančič, 1979), i.e. into the alliance Quercion roboris (or Genisto germanicae-Quercion roboris), which does not correspond to its full floristic composition. We therefore conducted additional comparisons with another two syntaxa, the association Seslerio autumnalis-Quercetum petraeae (Zupančič, 1999, Table 5, Poldini, 1982 Table 4, columns 27-34) and with the association Erico carne-ae-Quercetum petraeae (Krause and Ludwig, 1957: 118-120, Ritter-Studnička, 1970: 114-115, Beus, 1997. We also made a synthetic table (Table  3) with six columns and compared them with hierarchical classification and two-dimensional ordination (Figures 2 and 3). In terms of floristics, our stands are most similar to the stands of the association Melampyro-Quercetum petraeae. Floristic similarity with the association Seslerio autumnalis-Queretum petraeae according to Sørensen (1948) is already lower at about 45%. Similarity is only slightly higher (47%) with the most acidophilous form of this association described by Poldini (1982) as Seslerio autumnalis-Queretum petraeae avenelletosum flexuosae. It is differentiated by Castanea sativa, Luzula luzuloides, Avenella flexuosa and some other species. Poldini (ibid.) described two variants: the variant with Erica carnea on sites with less acid soil and the variant with Polytrichum formosum, Leucobryum glaucum, Genista germanica and Dicranum scoparium on more acid soil. He found such stands both on flysch and limestone. The tree layer is frequently dominated by Turkey oak (Quercus cerris). Poldini attributed the increased soil acidity to the past litter gathering. Despite certain similarities with the studied stands in the Vipavska brda (occurrence of Erica carnea, but with less medium coverage, and of some other acidophilous species except Vaccinium myrtillus), the dendrogram (Figures 2 and 3) shows the stands of the subassociation -avenelletosum flexuosae grouping with stands of other forms of the association Seslerio autumnalis-Quercetum petraeae and not with our community.
With consideration of the dominant species of the tree and herb layers, the studied stands could be classified into the association Erico carneae-Quercetum petraeae that was described in northern Bosnia (Krause and Ludwig, 1957: 90-91 and Table 1, column 3 on pages 118-120, Horvat, 1959: 30, Ritter-Studnička, 1970, but in very different ecological conditions, on serpentine bedrock (in western Bosnia the oak stands with Erica carnea were described also on Permian sandstones and on dystric soils and were classified into the syntaxon Betulo-Quercetum petraeae ericetosum -Fabijanić et al., 1963, Stefanović, 1984. Stands of this association are syndynamically closely related to the black and red pine on serpentinite (see also Horvat et al., 1974: 461) and their progressive development also leads to the (fir)beech forest. Floristic similarity of 23 relevés from the synthetic table of the association Erico-Quercetum petraeae Krause et Ludwig ex Horvat 1959 (the correct author citation, Theurillat, in litt.) -Ritter-Studnička (1970: 114-115) with our stands is only 20% according to Sørensen (1948), while floristic similarity of 5 relevés from the synthetic table of the same association (Krause and Ludwig, ibid.) is slightly higher (31%), which does not allow for its classification into the same association. In addition, Zupančič et al. (1986: 12) classify the association Erico-Quercetum petraeae into the alliance Quercion robori-petraeae = Quercion roboris and into the order Quercetalia roboripetraeae = Quercetalia roboris, while we classify the studied stands into the order Quercetalia pubescentipetraeae. Floristic dissimilarity is further confirmed by hierarchical classification (Figures 2 and 3).
Based on these comparisons, we decided to classify sessile oak stands from the Vipavska brda into the new association Chamaecytiso hirsuti-Quercetum petraeae ass. nov. hoc loco. Its diagnostic species are Quercus petraea (the edifier of all four compared communities that characterises the newly described association against the primary association Seslerio autumnalis-Fagetum), Erica carnea, Sorbus aria, Sesleria autumnalis, Chamaecytisus hirsutus, Lathyrus linifolius, Loranthus europaeus and Erythronium dens-canis. These species undoubtedly differentiate the studied stands both from floristically slightly similar stands of the associations Seslerio autumnalis-Quercetum petraeae and Melampyro-Quercetum petraeae as well as from physiognomically similar (with dominant Erica carnea in the herb layer) stands of the association Erico-Quercetum petraeae in Bosnia. The differential species that distinguish them from the stands of the association

ACKNOWLEDGEMENTS ZAHVALA
Oak forest research in the Vipava valley was partly conducted within the framework of the target research project Updating of the vegetation system for the forest management planning purposes (V4-1141), funded by the Slovenian Research Agency and Ministry of Agriculture and the Environment. Within the scope of this project, the Slovenian Forestry Institute conducted an analysis of the soil sample. I am sincerely grateful to Mag. Tomaž Prus and Dr. Milan Kobal for their help in the interpretation of soil conditions in the stands of the studied community. Matej Reščič and Klavdijo Čokelj helped me with their advice on the forest cover and the condition of forests on both the Vrhe plateau and in the hills of Vipavska brda. I am also grateful to Dr. Metka Culiberg, Prof. Dr. Andraž Čarni and Prof. Dr. Sead Vojniković for helping me to find and obtain relevant literature sources, as well as to Dr. Lado Kutnar and Dr. Andrej Rozman for valuable improvements of the text. I owe special thanks to Prof. Dr. Jean-Paul Theurillat for the literature he so kindly provided and for his advice on the correct author citation of the association Erico-Quercetum petraeae. Iztok Sajko prepared Figure 1 for print. English translation by Andreja Šalamon Verbič.