LOCALITIES AND SITES OF THE SOUTHEASTERN-ALPINE ENDEMIC SPECIES SPIRAEA DECUMBENS KOCH IN BREGINJSKI KOT (NORTHWESTERN SLOVENIA) NAHAJALIŠČA IN RASTIŠČA JUGOVZHODNOALPSKEGA ENDEMITA SPIRAEA DECUMBENS KOCH V BREGINJSKEM KOTU (SEVEROZAHODNA SLOVENIJA)

The eastern distribution limit of Spiraea decumbens s. str. is in Breginjski Kot (northwestern Slovenia), where we recorded 49 locali- ties of this eastern-Alpine endemic plant species. We determined two new localities in a new quadrant (9746/4) on riparian rocks of the Nadiža River under Mt. Mija at Kozja Peč, which is currently the southeasternmost point of its entire distribution area. We con- ducted a phytosociological survey of 26 localities. This endemic occurs in dolomite rock crevices in stands classified within the association Spiraeo-Potentilletum caulescentis . On dolomite screes and torrential fens it is found to dominate on small areas in the succes- sional stages, classified into the provisional association Aquilegio einseleanea-Spiraeetum decumbentis (alliance Petasition paradoxi ) and into the new association Spiraeo decumbentis-Seslerietum calcariae (alliance Caricion austroalpinae ). These stages are gradually becoming overgrown with thermophilous deciduous trees, and in one of the relevés we found the studied species in an open hop hornbeam stand classified into the association Fraxino orni-Ostryetum . Its populations are vital and unthreatened, except in the two new localities under Mt. Mija, which call for special protection due to their small size and a possibility of being backfilled with gravel.


INTRODUCTION UVOD
Spiraea decumbens is a southeastern-Alpine endemic plant species distributed in northeastern Italy and northwestern Slovenia.We distinguish two subspecies, S. decumbens Koch subsp.decumbens, which occurs in northwestern Slovenia and northeastern Italy, and S. decumbens subsp.tomentosa (Poech.)Dostal.= S. decumbens subsp. hacquetii (Fenzl & Koch) Arcang., which occurs in the eastern part of its distribution area, only in northeastern Italy (Aeschimann et al., 2004;Poldini, 2002).The distribution of this endemic plant species in Slovenia was discussed by Wraber (1969), Wraber and Skoberne (1989), Jogan (2000), Dakskobler (2003) and Čušin (2006).They reported the following localities: Tam v Klinu, Tam na Lepem Brdu under Mt.Mali Muzec (Musc), along the Bela above Breginj, at Most na Nadiži (Ponte Vittorio) and under Drnohla above the Učja valley.All its localities known so far in Slovenia have been under the Stol ridge above the Učja valley and in Breginjski Kot.Spiraea decumbens is listed as rare in the Red List (Anon., 2002).So far, we have conducted phytosociological investigations only of the sites in the rock crevices above the Učja valley, at Plazi and under the mountain pasture Ohoje in Breginjski Kot.These relevés were temporarily assigned to the association Potentilletum caulescentis s. lat.(Dakskobler, 2003).The purpose of our study was to record as many localities of this rare endemic species in Breginjski Kot as possible, to study the plant communities on its sites and assess its vitality and potential threat.

Ecological description of the study area Ekološki opis raziskovanega območja
Breginjski Kot is situated at the foothills of the Julian Alps and is the westernmost part of Slovenia.It is surrounded by the Stol Mountains in the north, the Nadiža River in the west, by mounts Mija and Ljubija in the south and extends into Staroselsko Podolje lowland in the east.The region has a moist climate with mean annual precipitation exceeding 2500 mm and periodically heavy rain.The bedrock at higher elevations is composed of hard calcareous rocks, dolomite, dolomitised limestone and limestone, while the sub-montane belt is dominated by flysch and glacial deposits.The vegetation reflects strong anthropozoogenous influence.Steep and stony areas that were unsuitable for farming are overgrown with forest.Other areas are mainly covered by grasslands that have been subjected to rapid overgrowing in recent decades.The composition of the local flora is dominated by plants of the moderate climatic belt and plants that belong to the boreal geoelement.There are many Mediterranean-montane, Mediterranean and Illyrian species, of which 23 are endemic, mainly southeastern-Alpine (Čušin, 2006).

MATERIALS AND METHODS MATERIALI IN METODE
In Breginjski Kot, we examined the areas with already known localities and the areas where this species could potentially occur.We used the GPS receiver and a synoptic map where we marked the localities.The coordinates of the localities were entered into the FloVe-gSi database (Seliškar et al., 2003).For a more detailed analysis we selected six areas where we made 26 relevés, applying the standard Central-European method (Braun-Blanquet, 1964).These relevés were entered into the FloVegSi database.Combined cover-abundance values were transformed into ordinal values 1 -9 (van der Maarel, 1979).Numerical comparisons were made with the software package SYN-TAX 2000(Podani, 2001).Relevés were arranged into the analytic table (Table 1) based on hierarchical classification and assessment of diagnostic species.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 numerous authors.The nomenclature source for the names of vascular plants is Martinčič et al. (2007), and Martinčič (2003Martinčič ( , 2011) ) for the names of mosses.The nomenclature source for the names of syntaxa is Šilc and Čarni (2012).On each locality we determined the size of the populations and assessed their vitality and potential threat.Vitality was scored on a scale where 1 = poor, 2 = moderate and 3 = good.

RESULTS AND DISCUSSION REZULTATI IN RAZPRAVA 3.1 Phytosociological description of the sites of
Spiraea decumbens in Breginjski Kot 3.1 Fitocenološka oznaka rastišč vrste Spiraea decumbens v Breginjskem kotu The 26 relevés in Table 1 were arranged based on hierarchical classification and with consideration of diagnostic species.We found that the relevés in rock crevices and ledges are floristically very similar to those on steep gravel directly under rock faces, as chasmophytic species frequently occur also on screes, and vice versa.Spiraea decumbens usually spreads abundantly on screes and its coverage is considerably higher there than in rock crevices.Relevés 1 and 2 in Table 1 that were made in the area of Kozja Peč are unique and cannot be adequately syntaxonomically classified as yet, but they belong to a chasmophytic community (class Asplenieta trichomanis).Relevés 2 to 10 in Table 1 can be classified into the association Spiraeo decumbentis-Potentilletum caulescentis Poldini 1969.Compared with the stands of this association in the Carnic Alps and in the Italian part of the Julian Alps (Poldini, 1973) they are somewhat floristically impoverished.Some of the species, for example Leontodon tenuiflorus, Athamanta turbith, Primula auricula, which are common or diagnostic in the original table of this association, were therefore not recorded on our plots.Our stands are treated as a special variant with Rhodothamnus chamaecistus, which very rarely occurs in relevés from Italy.The differential species of the variant is also Campanula cespitosa.Relevés 12 to 16 in Table 1 characterise small ledges or steep screes under rock faces, i.e. scree vegetation, which is in fact usually dominated by Spiraea decumbens.For the time being, these stands are named after Spiraea decumbens and Aquilegia einseleana as the provisional associati-on Aquilegio einseleanae-Spiraeetum decumbentis nom.prov.Its diagnostic species are Spiraea decumbens and Aquilegia einseleana, and its differential species are Salix glabra, Campanula cespitosa, Leontodon hispidus subsp.hyoseroides and Rhamnus pumilus.This is a successional stage that occurs in small areas (from 2 m 2 to 10 m 2 ) on initial soil (lithosol) in the overgrowing of dolomite gravel or of rock ledges.It is characterised by coexistence of chasmophytic species, scree species and species of stony subalpine grasslands.This stage, which requires further investigation, is temporarily classified into the alliance Petasition paradoxi, order Arabido alpinae-Petasitetalia paradoxi and class Thlaspietea rotundifolii.Relevés 17 to 25 in     This area comprises the river bed of a torrential tributary of the Bela, which is in the process of becoming overgrown.Its catchment area is under Mt.Musc.The overgrowing of screes began after 1933 when concrete torrential barriers were built there.This reduced flow velocity and prevented transportation of gravel.During the construction of barriers on the Bela, a large area was reforested, mainly with the conifers Picea abies, Pinus nigra, Pinus sylvestris, Larix decidua (Kočar, 1999).In this area, Spiraea decumbens grows between the last and its preceding barrier at the elevation between 695 m and 820 m.Nine relevés were made there.The geological bedrock is talus or dolomite rock.Spiraea decumbens grows in two basic vegetation types, in stony grassland on overgrown scree (Spiraeo decumbentis-Seslerietum calcariae) and in a chasmophytic community (Spiraeo decumbentis-Potentilletum caulescentis).Especially interesting is the secondary locality in the crevices on the uppermost concrete torrential barrier.Researchers have not reported such secondary localities for Slovenia until now, or they have not been known.Wraber (1969) saw them in Pušja Vas (Venzone) in Italy, where Spiraea decumbens grows on  old walls.Most localities are on gentle slopes facing south and southeast; the slope ranges between 5º and 35º, except on two localities where it reaches 80º and 90º, respectively.The area occupied by Spiraea decumbens varies, ranging from 2.5 m 2 to 12 m 2 in size.On most of the plots it covers between 25 % and 50 % of the surface area (value 3), but it is very scarce on two plots where it covers only a small part of the surface area (value +).The shrubs on stony grasslands grow to be the tallest, reaching up to 40 cm in height.Shrubs growing on the scree and in rock crevices are slightly shorter, up to 20 cm.The population is vital and not potentially threatened.

Spiraea decumbens
Prekopa is a botanically fascinating area with several habitats listed in Annex I to the Habitats Directive (Čušin, 2006).The slope gradient contributes to the erodibility of the dolomite slopes and the overgrowing of screes is very slow.Screes face towards the (south) east and (south)west and there is a mountain trail leading across the ridge towards Mt.Musc.All localities (six relevés) are on the top of the eastwards facing scree, but we did not find any localities on the western side.The elevation ranges between 900 m and 920 m, the geological bedrock is talus or dolomite.Two vegetation types prevail: scree community (Aquilegio einseleanae-Spiraeetum decumbentis) and chasmophytic community (Spiraeo-Potentilletum caulescentis).Spiraea decumbens localities face north, northeast, east and southeast, on slopes of 40° to 95°.The smallest sample plot measures 2 m 2 and the largest 21 m 2 .Spiraea decumbens coverage varies among plots; it was assessed as + on three plots and as 1, 2 and 3 on the remaining three (according to the Braun-Blanquet scale, 1964).Shrub height does not exceed 20 cm.The population is vital and not potentially threatened.

Area Breginj-Plazi Območje Breginj-Plazi
Plazi is situated to the west of Prekopa.This area comprises known localities of several eastern-Alpine taxa that are rare in Slovenia: Thesium rostratum, Physoplexis comosa and Paederota bonarota.The first locality of Spiraea decumbens is only about a metre away from the road, on an already heavily overgrown slope planted with black pine.Other localities are situated at the bottom of two narrow gorges of the Plazi stream and on precipitous rock faces.It is in these two gorges that Spiraea decumbens population is the most abundant.The localities were recorded at 790 m to 820 m a.s.l., but Spiraea decumbens can grow even higher here, up to 1000 m a.s.l.The bedrock on four plots is dolomite and talus on one plot.Localities face different directions: west, northeast, south and east.Three plots, where we recorded a chasmophytic community, have a slope of 90° to 100° and two plots have a slope of 40° or 50°.The smallest plot measures 2 m 2 and the largest 12 m 2 .On most plots, Spiraea decumbens covers less than 10 % of the surface area (value 1), whereas on one plot of 7 m 2 it covers more than 50 % of the surface area.Shrub height ranges from 20 cm in rock crevices to 35 cm on scree.The Spiraea decumbens population on this locality is the largest, vital and not threatened.
3.3.4Area Breginj-Benetke 3.3.4Območje Breginj-Benetke This is a steep dolomite erodible area of about 0.05 km 2 to the west of Plazi.We made three relevés on spots that are not subject to erosion and allow for the growth of Spiraea decumbens.These localities are situated at an altitude between 820 m and 850 m.Above the mountain pastures Ohoje and Javornik, localities can be found as high as 1200 m.One plot is on slightly overgrown scree and two are in rock crevices.The localities face south, north and northwest.The slope on two plots is 40° and 100° on the third.The population of Spiraea decumbens is small here, with the largest plot measuring 4 m 2 and the smallest only 1.5 m 2 .Spiraea decumbens covers more than 50 % of the surface area on two plots and less than 10 % on the third.Shrub height does not exceed 25 cm.The population is vital and not threatened.
3.3.5Area Breginj-Klin 3.3.5Območje Breginj-Klin The locality is situated on heavily overgrown scree, in an open forest stand on rendzina at about 100 m above the mountain trail leading to Brezje (Montemaggiore) village in Italy.The tree layer covers 70 %, the shrub layer 10 % and the herb layer 80 % of the plot.Only one locality nearby has a higher coverage, but could not be recorded because of the damages caused by sleet.The trees here are up to 6 m high and not thicker than 20 cm.Thermophilous deciduous trees form the tree and the shrub layer: Fraxinus ornus, Ostrya carpinifolia and Sorbus aria.Fagus sylvatica and Acer pseudoplatanus occur in the herb layer along with manna ash and whitebeam.The geological bedrock consists of talus.The plot is situated 820 m a.s.l. and faces west.The slope gradient is 25°.Spiraea decumbens grows in an area of 20 m 2 and covers less than 50 % of the surface area.The tallest specimen of Spiraea decumbens was measured here at 50 cm, whereas most shrubs on the plot reach the average height of 30 cm.While vital, the population may become near threatened if the overgrowing of the scree continues.There is only one shrub on each, which leads to the conclusion that the seeds were deposited by the Nadiža from its headwaters (hydrochory).The elevation of the plots was around 265 m, the slope 70° towards northwest (the first plot) and 90° towards north (the second plot).In contrast to other 24 plots, the geological bedrock under Mija consists of limestone.The plot with easier access measures 1.5 m 2 with Spiraea decumbens covering less than 10 %.The tallest specimens are below 30 cm and are vital.The river flow in this part is periodically regulated through gravel excavation and could become backfilled, so we alerted the Institute for Nature Conservation about this locality.The second locality under Kozja Peč is in much less accessible rocks above the Nadiža pool and could be threatened by visitors who come here for a summer swim.The distribution map of Spiraea decumbens in Slovenia with marked new locality is shown in Figure 3. nus ornus and Sorbus aria, sporadically also with individual Pinus nigra trees.Despite several attempts, we did not manage to confirm the Spiraea decumbens locality at the gravel bar on the Nadiža that had been reported by Wraber (1969) and which Čušin (2006) had failed to find as well.However, we found two new localities in the new quadrant (9746/4) at the northern foot of Mt.Mija, at Kozja Peč on the right bank of the Nadiža River.These two localities differ from all other localities investigated in our study, both in terms of ecology (the geological bedrock is limestone) and floristics.Only two clusters of Spiraea decumbens overgrow steep riverine rocks and overhangs.We assume that its seeds had been deposited here by water.Spiraea decumbens is potentially threatened by swimmers in the new localities under Mija and even more by gravel extraction that takes place with the regulation of the river bed.This small population should therefore be carefully monitored and protected, especially because it is the southeasternmost locality in its entire distribution area.On other localities, Spiraea decumbens thrives either in small patches or tufts, or in large clusters in areas ranging from 1.5 m 2 to 24 m 2 in size.The largest population of Spiraea decumbens was found in the area Plazi, where favourable site conditions facilitate its growth in a larger area (screes, rock barriers and solitary rocks).The vitality of individuals on most localities is good, even on slightly shaded sites.Dry individuals that have probably died off because of their physiological age are only rarely observed.The species also regenerates well, although only in limited areas.All this points to predominantly vegetative propagation, which is most distinct in rock crevices.

ACKNOWLEDGEMENTS ZAHVALA
The study is the result of the graduation thesis (Pavlin, 2015) written by the younger author under the mentorship of the senior authors.Sincere thanks to Prof. Dr. Franc Batič for his insights and comments.Dr. Lado Kutnar and Dr. Aleksander Marinšek helped us with valuable improvements and corrections.English translation by Andreja Šalamon Verbič.

Fig. 2 :
Fig. 2: Localities of Spiraea decumbens under Mt.Mija (Kozja Peč) 3.3.6Area Nadiža-Kozja Peč 3.3.6Območje Nadiža-Kozja Peč At the foothills of Mija, under Kozja Peč on the right bank of the Nadiža, Marko Pavlin, the youngest of three authors, discovered on 20 June 2014 two new localities of Spiraea decumbens in the new quadrant 9746/4, about 400 m air distance apart.Igor Dakskobler picked a specimen for the Herbarium of the Institute of Biology SRC SASA (LJS) on 11 July 2014.These are for now the southeasternmost localities in the entire distribution area of this species and the first in the Mija Mountains.All other localities in the territory of Slovenia are in the Stol Mountains.

Fig. 8 :Fig. 9 :
Fig. 8: Secondary locality of Spiraea decumbens in the crevices on the uppermost concrete torrential barrier in the channel of a torrential tributary of the Bela.Photo: M. Pavlin

sified into the association Fraxino orni-Ostryetum. An example of such an open forest can be seen in relevé 26 inTable 1 .
Table 1 represent the next stage in succession, extensively overgrown established screes or gravelly grasslands in erosion areas that are very slowly becoming overgrown with shrub and tree species.These stands are classified into the new association Spiraeo decumbentis-Sesleriete-Synsystematic classification of the studied communities into higher units is as follows: Class: Asplenieta trichomanis (Br.-Bl. in Meier & Br.Bl. um calcariae ass.nov.Its diagnostic species are Spiraea decumbens, Sesleria caerulea subsp.calcaria, Erica carnea, Polygala chamaebuxus, Molinia caerulea subsp.arundinacea, Allium ericetorum, Polygala nicaeensis subsp.carniolica (= P. nicaeensis subsp.forojulensis) and Chamaecytisus purpureus.The nomenclature type of the new association, holotypus, is relevé 21 in Table 1.The new association is classified into the alliance Caricion austroalpinae, order Seslerietalia coeruleae and class Elyno-Seslerietea.In the next stage of succession, these overgrown screes are sometimes covered with open Ostrya carpinifolia and Fraxinus ornus forest clas-