PHYTOSOCIOLOGICAL DESCRIPTION OF THE DWARF MOUNTAIN PINE SHRUB COMMUNITY ( AMELANCHIERO OVALIS-PINETUM MUGO ) IN THE VALLEYS OF THE SLOVENIAN ALPS FITOCENOLOŠKI OPIS GRMIŠČNE ZDRUŽBE DOLINSKEGA RUŠEVJA ( AMELANCHIERO OVALIS-PINETUM MUGO ) V SLOVENSKIH ALPAH

We have expanded our knowledge of the localities, sites and distribution of the Amelanchiero ovalis-Pinetum mugo association in the Slovenian Alps. Based on phytocenological analyses, the shrub association belonging to the forest vegetation type Alpine mountain pine scrub was divided into two subassociations: peucedanetosum oreoselini and hylocomiadelphetosum triquetri . We also described four variants within the latter association.


INTRODUCTION UVOD
The phytocenological problematics of valley dwarf mountain pine scrub in the southern and southeastern Alps were presented in more detail several years ago (Dakskobler, 2014). The Amelanchiero ovalis-Pinetum mugo association has been described in northern Italy, in the Trento region, and is also known in Friuli-Venezia Giulia (Minghetti, 1996;Poldini and Vidali, 1999;Poldini et al., 2004) and in the Austrian part of the Karavanke Mountains, near Borovlje / Ferlach (Franz, 2020). Zupančič et al. (2006), in a synthetic review of Alpine dwarf mountain pine scrub in Slovenia, placed it in the rank of the Rhodothamno-Rhododendretum hirsuti form Amelanchier ovalis (= Rhodothamno-Pinetum mugo form Amelanchier ovalis). However, in our work (Dakskobler, 2014) we considered that the dwarf mountain pine scrub, which grows in the Julian Alps in warm spots at the ends of alpine valleys or on very steep, crumbly dolomite slopes in the mountain beech forest belt, could be classified in the Amelanchiero ovalis-Pinetum mugo association on the basis of its floristic composition. It is a long-lasting pioneer stage on extreme sites where natural factors such as erosion and avalanches prevent its development into beech forest. Although it does not contain all the diagnostic species of this association described in northern Italy, the frequent presence of the species Amelanchier ovalis, Fraxinus ornus, Ostrya carpinifolia, Hieracium porrifolium and Frangula alnus distinguishes it well from the Rhodothamno-Pinetum mugo scrub widespread in the altimontane and subalpine belt of the Julian Alps, including its most thermophilic form, Rhodothamno-Pinetum mugo typicum var. Genista radiata. On the basis of inventories from the Julian Alps, we described a new geographical variant, var. geogr. Rhamnus fallax. We divided the stands into two site variants, var. Peucedanum oreoselinum and var. Carex firma, and also mentioned the occurrence of this community in the Karavanke and Kamnik-Savinja Alps. A year later, we presented the valley dwarf mountain pine scrub in the Slovenian Alps in a popular scientific way (Dakskobler et al., 2015). A few years later (Dakskobler, 2019), we published two additional relevés from the Kot Valley, which we classified in a provisional new subassociation laricetosum deciduae. In the overview of forest vegetation types of Slovenia (Bončina et al., 2021), we classified the valley dwarf mountain pine scrub into the forest vegetation type Alpine dwarf mountain pine scrub. The syntaxonomic description of this vegetation type also includes the association Amelanchiero ovalis-Pinetum mugo, its geographical variant Rhamnus fallax and three subassociations typicum, caricetosum and laricetosum, but which are not based on validly described syntaxa (Theurillat et al., 2021). The lower syntaxonomic units of this association were therefore examined in the present paper, which also considered relevés from the Karavanke and Kamnik-Savinja Alps, in addition to previously published relevés from the Julian Alps (Dakskobler, 2014;2019).

METHODS METODE
The valley dwarf mountain pine scrub was inventoried according to the Central European method (Braun-Blanquet, 1964). Phytocenological relevés were en-tered into the FloVegSi database (Seliškar et al., 2003). The combined estimates of cover and abundance were converted to ordinal values from 1 to 9 (van der Maarel, 1979). The relevés were compared by hierarchical classification and numerical ordination using principal coordinate analysis (PCoA, Wishart's coefficient of similarity) and ordered in Table 1 based on the results of the clustering method using the unweighted pairgroup method with arithmetic mean (UPGMA), where the Wishart's coefficient of similarity (similarity ratio) was also chosen. Ecological conditions were determined using Ellenberg-type indicator values (Tichý et al., 2023), where estimates of environmental conditions for relevés were calculated from indicator values of herbaceous layer plant species using a weighted arithmetic mean. The software package SYN-TAX 2000(Podani, 2001 and the R software environment (R core team, 2022) were used for all analyses. Geoelementary, ecological and phytoecological descriptions of plant species were taken from Flora alpina (Aeschimann et al., 2004a;2004b). Nomenclatural sources for ferns and higher plants are Martinčič et al. (2007) and the FloVegSi database; for mosses Hodgetts et al. (2020); for lichens Suppan et al. (2000); and for syntaxonomy Zupančič (2007;2013), Šilc and Čarni (2012), Dakskobler et al. (2015) and Bončina et al. (2021). Those species that are not listed in the nomenclatural source are written with the full name and author.

Opis ugotovljenih sintaksonov
The relevés of valley dwarf mountain pine scrub from the mountain elevation zone (between 750 m and 1150 m, with only one stand above 1200 m) of the Julian Alps, the Karavanke Mountains and the Kamnik-Savinja Alps (Fig. 1) were divided into three main groups based on hierarchical classification. These relevés were arranged in Table 1 according to the dendrogram (Fig. 2), also taking into account the diagnostic species identified during the classification process.
To the diagnostic species of the association Pinus mugo, Amelanchier ovalis, Ostrya crapinifolia, Fraxinus ornus, Hieracium porrifolium and Frangula alnus, we added two more, Molinia arundinacea and Campanula cespitosa. Both are rare in stands of subalpine dwarf mountain pine scrub (Rhodothamno-Pinetum mugo) and more common only in stands of the syntaxon Rhodothamno-Pinetum mugo typicum var. Genista radiata (Dakskobler, 2014). Although the dendrogram (Fig. 2) and, to some extent, the ordination diagram ( Fig. 3) indicate three groups of relevés, we believe that the existing relevés only provide a basis for describing the two subassociations. The subassociation Amelanchiero ovalis-Pinetum mugo peucedanetosum oreoselini subass. nov. hoc loco includes relevés nos. 1-7. Its nomencla-tural type, holotypus, is relevé no. 2 in Table 1. The differential species of the subassociation are Peucedanum oreoselinum, Genista radiata, Viola hirta, Leucanthemum heterophyllum, Teucrium montanum and Inula ensifolia. Thus, the new subassociation includes stands that were considered to belong to the variant with Peucedanum oreoselinum a few years ago (Dakskobler, 2014). Most of the relevés were made in the Tolminka Valley (Gnelice) in the southern Julian Alps, but only one relevé was made in the Mala Pišnica Valley (in the northeastern Julian Alps). This is a form of valley dwarf mountain pine scrub from warmer sites, which is also most similar to stands of this association as described in northern and northeastern Italy (see Dakskobler, 2014,  Tofieldia calyculata, Heliosperma alpestre, Gymnocarpium robertianum, Salix appendiculata, Primula wulfeniana, Paederota lutea, Pinguicula alpina, Senecio abrotanifolius, Vaccinium myrtillus and V. vitis-idaea. These species are characteristic of the colder sites of valley dwarf mountain pine scrub in areas where snow remains longer. This subassociation also includes stands of the provisionally described subassociation laricetosum deciduae (Dakskobler, 2019).
The phytocenoses of this subassociation are divided into four variants. The relevés of the variant with Convallaria majalis (two from the Struje erosion area in the Tolmin Julian Alps, one from the Zadnjica Valley in Trenta, relevés nos. 8-10) are most similar in terms of species composition to the stands of the peucedanetosum oreoselini subassociation.
Most of the relevés of the Homogyne sylvestris variant (its differential species is also Galium austriacum, relevés nos. 11-17) were made in the eastern Karavanke Mountains, in the Peca Mountains, Topla Valley and torrential-erosion area of Šodri; only one relevé was from the Zadnjica Valley in Trenta. A characteristic feature of these stands is the sparse occurrence of some of the characteristic species of the association (Ostrya carpinifolia and Fraxinus ornus were not found in the stands in the Topla Valley). Therefore, their inclusion in this association is legitimate, while these stands are grouped with the other stands of the Amelanchiero-Pinetum mugo association and are not completely separated from the other inventories.
The variant with Omphalodes verna (relevés nos. 18-20) includes relevés from the western Karavanke Mountains, from the Draga Valley near Begunje. Aquilegia nigricans, Festuca amethystina and Chamaecytisus purpureus are also its differential species. These are the lowest stands of this association in Slovenia, with  an altitude of only 750 m to 880 m. All characteristic species of the association are represented in them, but among the differentiated species of the subassociation there is no European larch (Larix decidua). However, since they are grouped together with the relevés of the two previous variants, they are assigned to the subassociation hylocomiadelphetosum triquetri. It is likely that these stands could be placed in their own subassociation due to a greater number of relevés.
Relevés nos. 21-27 are classified in the variant Carex firma. Differential species also include Pyrola rotundifolia, Salix eleagnos, Astrantia carniolica, Trisetum argenteum and Aquilegia iulia Nardi. The localities are the Možnice and Kot Valleys (both in the Julian Alps) and Ravenska Kočna in the Kamnik-Savinja Alps. These are dwarf mountain pine stands on alluvial-glacial deposits, on gravel and rubble, near occasional watercourses, as indicated by the differential species of the variant, including grey willow (Salix eleagnos) and the scree species Trisetum argenteum and Aquilegia iulia. Also some of the association differential species (Ostrya carpinifolia, Fraxinus ornus) are very rare or absent in these relevés, as in the Kot Valley and Ravenska Kočna, but the subassociation differential species are well represented there.
The differential species of the geographic variant Rhamnus fallax is common only in stands of the subassociation peucedanetosum oreoselini, but it also occurs sporadically in stands of the subassociation hylocomiadelphetosum triquetri. The range of the species Rhamnus fallax in Slovenia (see Dakskobler et al., 2013: 103) overlaps with the range of the association Ame-lanchiero ovalis-Pinetum mugo in Slovenia (the only exception could be the Topla Valley, where this species has not yet been recorded in quadrant 9545/2). Therefore, we consider all syntaxa described in this paper within the geographical variant Amelanchiero ovalis-Pinetum mugo Minghetti and Pedrotti 1994 var. geogr. Rhamnus fallax Dakskobler 2014.

Ecological characteristics of the detected syntaxa Ekološka oznaka ugotovljenih sintaksonov
The inventoried stands of valley dwarf mountain pine scrub are at elevations between 750 m and 1230 m. In general, the stands of the A-P peucedanetosum oreoselini subassociation grow at a slightly lower elevation than the stands of the A-P hylocomiadelphetosum triquetri subassociation, except for the stands in the Draga Valley, which are assigned to the Omphalodes verna variant. The stands of dwarf mountain pine on alluvial-glacial deposits, on gravel and rubble in the Ravenska Kočna, Možnica and Kot Valleys, which we classified as variant A-P hylocomiadelphetosum var. Carex firma, grow on gentle slopes up to 10°, while the stands of the other variants of this subassociation grow on steeper dolomite slopes of 30°-45°; they are classified as variant A-P hylocomiadelphetosum var. Carex firma. The slope of the relevés of the stands of the peucedanetosum oreoselini subassociation is gentle to steep ( Fig. 3 and Fig. 4).
Using Ellenberg-type indicator values (Tichý et al., 2023), we found significant differences between the  considered syntaxa only in the estimates for temperature and humidity ( Fig. 3 and Fig. 5). Stands of subassociation A-P peucedanetosum oreoselini grow under the warmest conditions, where we also found significantly lower moisture content at the site (Anova, Tukey post-hoc test, p < 0.05).
We counted 242 taxa of higher plants and 19 species of mosses in the valley dwarf mountain pine stands. Among them, 11 species were found in the tree layer, 44 species in the shrub layer, and 187 taxa (species and subspecies) in the herb layer of higher plants. The moss layer is incomplete, as only the most common taxa have been identified so far, while others have been collected and are still awaiting determination. On average, 52 taxa (ranging from 25 to 73) were present in an relevé area of 100 m 2 to 400 m 2 (plot size was adjusted to the homogeneity of the plot). The most speci-es-rich stands were those of the variant A-P hylocomiadelphetosum triquetri var. Carex firma, which grows on alluvial-glacial material at the bottom of alpine valleys, while slightly fewer species were found in the stands of the variants Homogyne sylvestris and Convallaria majalis, which dominate in erosion areas. The Shannon-Wiener index of species diversity shows a similar pattern to the number of species per relevé plot ( Fig. 3 and Fig.  6).

Overview of established syntaxa and their classification into higher syntaxonomic units Pregled in sinsistematska uvrstitev obravnavanih združb v višje enote
The assemblage is classified into the following higher synsystematic units:   The classification in the monograph on forest vegetation types of Slovenia (Bončina et al., 2021)

CONCLUSIONS ZAKLJUČKI
Dwarf mountain pine scrub, found in the valleys of the Slovenian Alps at altitudes between 750 m and 1150 m (exceptionally higher, above 1200 m), is known in the Tolminka, Možnica, Zadnjica and Kot Valleys, as well as on the slopes above the Mala Pišnica Valley in the Julian Alps, in the Draga Valley in the western Karavanke, in the Topla Valley in the eastern Karavanke, in Ravenska Kočna in the Kamnik-Savinja Alps, and probably elsewhere in these mountains. It differs somewhat in appearance and structure from the subalpine-alpine dwarf mountain pine scrub of the southeastern Alps. It thrives on special sites, in erosion are- as, on torrential fans and on alluvial-glacial deposits, especially in the montane beech forest belt. It serves as a long-lasting successional stage where conditions are too extreme for more demanding tree species, such as beech, to thrive. It is characterised by a diverse species composition that includes typical species of pine, spruce, beech and oak-hop hornbeam forests, as well as species of scree, rock crevices, the subalpine zone and dry mountain meadows. Although it usually still contains two characteristic species of subalpine-alpine dwarf pine scrub, Rhodothamnus chamaecistus and Rhododendron hirsutum, its overall species composition and pioneer character allow it to be classified as an independent association Amelanchiero ovalis-Pinetum mugo, as has already been done in some alpine areas of northern Italy. We have described two of its new subassociations, peucedanetosum oreoselini (its stands are most similar to those in northern Italy and hylocomiadelphetosum triquetri. Some stands of the latter could also be considered on the rank of a particular elevational (valley) form of Amelanchier ovalis, as suggested by Zupančič et al. (2006), or as a particular subassociation of amelanchieretosum ovalis, within the Rhodothamno-Pinetum mugo association.
Valley dwarf mountain pine scrub is not of great importance in the forest area of Slovenia because of its small size, and has therefore been added to the Alpine dwarf mountain pine scrub type in terms of forest vegetation types. The importance of these scrub stands is mainly protective, as they prevent erosion. In some places these stands are located along mountain paths (e.g. in the Ravenska Kočna, Tolminka, Zadnjica and Kot Valleys), where they can be partially cleared by humans, which is strongly discouraged. It may be threatened by forest fires, avalanches, torrents, rockfall, prolonged drought and fungal diseases.