Pinus mugo shrubs on peat bogs in the Tatra National Park

Pinus mugo shrubs on peat bogs in the Tatra National Park (TNP) were for the first time described as a separated plant association by Obidowicz (1975) from only two mires. Since then, there have been no studies on peat bogs in the TNP and they have not been mentioned in the list of vegetation types of the Park. The research regarding the dwarf pine shrubs on mires in the Tatra Mountains was carried out in 2019. We mapped all patches of such vegetation (total ~2 ha) on which we made 26 relevés. P. mugo shrubs on peat bogs occur within the complex of mire habitats, such as Norway spruce bog woodlands, raised bogs and poor fens. The shrub layer is dominated by Pinus mugo with admixture of dwarfish Picea abies. Typical plants of the herb layer are Vaccinium myrtillus, V. vitis-idaea, Eriophorum vaginatum and Oxycoccus palustris, whereas the most common mosses are Sphagnum magellanicum, S. capillifolium, S. russowi, Pleurozium schreberi. P. mugo shrubs on peat bogs in the TNP belong to the association Sphagno magellanici-Pinetum mugo.


Introduction
Pinus mugo shrublands occur in Central Europe in two major types: (1) subalpine, such as Seslerio albicantis-Pinetum mugo (Šoltésová 1974) Šibík in Jarolímek et Šibík 2008, Adenostylo alliariae-Pinetum mugo (Sillinger 1933 Šoltésová 1974, Dryopterido dilatatae-Pinetum mugo Unar et al. 1985, Cetrario islandicae-Pinetum mugo Hada 1956, and(2) azonal peat bog communities (Šibík et al. 2010). Dwarf pine (Pinus mugo) shrubs on peat bogs occur in the Carpathians, Sudetes, Alps, Dinarids, Rila and Pirin Mountains (Šibík et al. 2010). They grow in the montane and subalpine zones between 700-1800 m a.s.l. (Šibík et al. 2008). In Poland, studies regarding these shrublands were carried out in the Sudetes (Potocka 1997(Potocka , 2001, whereas in the Tatras they were not sufficiently described. First phytosociological studies in the Tatra Mountains did not include P. mugo shrubs on peat bogs as a separate plant association. However, Szafer et al. (1927) in their work regarding the vegetation of Kościeliska Valley mentioned such a plant community as a successional stage on peat bogs at the foothills of Tatras. In the phytosociological table of dwarf pine shrubs, they included 5 relevés with abundant occurrence of Sphagnum capillifolium. Pawłowski et al. (1928) in their work concerning the plant communities of Rybi Potok Valley (High Tatras) also described vegetation of Rybie Stawki mires. The description included P. mugo krummholz. Unfortunately, there is lack of information regarding their characteristics, especially moss layer. Obidowicz (1975) was the first who described P. mugo shrubs on peat bogs from the Polish Tatras. He described them as Pinus mugo-Vaccinium uliginosum community from two mires, Toporowy Staw Wyżni (variant with Empetrum nigrum) and Pańszczycka Młaka. Balcerkiewicz (1984), in his work regarding the vegetation of Pięć Stawów Polskich Valley, mentioned the P. mugo krummholz dominated with Sphagnum mosses. There is no information about dwarf pine shrubs on peat bogs in the floristic documentation prepared for the Management Plan of Tatra National Park (Mirek et al. 2013a, b). Therefore, they are also not included as a plant association in the Management Plan of Tatra National Park (Rozporządzenie… 2021). However, the description of the Natura 2000 habitat Bog woodlands in the Tatras shows that this habitat also encompasses such shrublands.
The aim of this work was to characterize P. mugo shrubs on peat bogs in the Tatra National Park based on the relevés collected within the entire range of these shrublands.

Materials and methods
This study was conducted in the Tatra National Park, encompassing 211.8 km 2 and protecting the entire area of the Polish Tatra Mountains, the highest range of the Carpathians (Fig. 1) P. mugo shrubs on peat bogs occur within the complex of mire habitats, such as Norway spruce bog woodlands, raised bogs and poor fens (Figs 2-3). Their patches cover a relatively small area in the Tatra National Park (few hectares - Mirek et al. 2013b, unpubl.). They emerged between the ridges of lateral moraines and slopes of the valleys and between the ridges of recessional moraines. In the second case, they emerged mostly in kettle holes (Derkacz 2006;Łajczak 2014;Zasadni 2015). Both the area and thickness of peat are diversified. Most of the mires are topogenic with only a few of them being typical ombrotrophic bogs. Some wetlands represent both types.
P. mugo shrubs on peat bogs were mapped in the vegetation period of 2019, based on the topographic method (Faliński 1990). Field mapping was done using the GPS etrex 30x. Furthermore, we made 26 relevés in these shrublands (Braun-Blanquet 1964, Dzwonko 2007. The area of relevés varied from 50 to 100 m 2 . In a single case, the area was smaller at 25 m 2 . We detected 14 patches of P. mugo shrubs on peat bogs in the Tatra National Park. Their total area covers ~2 ha. They occur on flat terrains between 1177-1640 m a.s.l. Geological substrate consists of peats and peat loams (SMGT 2016) on which peat soils emerged (Skiba et al. 2015).
We mapped all patches of dwarf pine shrubs on peat bogs in the montane zone of Tatra Mountains. P. mugo krummholz on peat bogs in the subalpine zone (above timberline) were not a subject of this research, except two mires located in the Goryczkowa Valley and in the vicinity of Litworowy Staw. There are a few patches of such shrublands in the subalpine zone of Gąsienicowa and Pięć Stawów Polskich Valleys and probably in other parts of the Tatras as suggested by data from relevés made by Szafer et al. (1927). However, it is difficult to find them in the dense subalpine thickets of P. mugo.

Results
P. mugo is a dominant species in all patches of studied shrublands, accompanied by Picea abies. The most common plants in the herb layer are Vaccinum myrtillus, V. vitis-idaea, Eriophorum vaginatum and Oxycoccus palustris ( Fig. 4E-H). The latter two were not found only on Butorów peat and in a single relevé in Tomanowa Valley. These are peat bogs with relatively tall and most dense krummholz of P. mugo. The moss layer is dominated by Sphagnum magellanicum, S. capillifolium, S. russowi and Pleurozium schreberi (Table 1). According to Matuszkiewicz (2008), the characteristic species of Pino mugo-Sphagnetum which were found in the analyzed patches are P. mugo and Melampyrum pratense. Furthermore, common species that occur in these shrublands are those representing the alliance of acidophilous Norway spruce forests (Piceion abietis) such as Homogyne alpina, Listera cordata, Picea abies and S. girgensohnii. The characteristic plants for Typical species for raised bogs (Oxycocco-Sphagnetea) are Aulacomnium palustre, Calypogea azurea and Sphagnum russowi (Table 1). It is worth adding that species representing order Caricetalia nigrae, such as Carex echinata, Carex nigra, Juncus filiformis, Viola palustris, also occur in the patches of P. mugo shrubs on peat bogs in the Tatra Mountains, however, their constancy is relatively low (Table 1).     . .

Sphagnum magellanicum
Characteristic and differential species were given according to Matuszkiewicz (2008), with the exception of those marked with an asterisk ( * ), which were given according to Hadač et al. (1969).

Peat bogs description
1. Butorów -rel. 1A-C, Fig. 4C -two patches of P. mugo shrubs -large patch, surrounded by Norway spruce bog woodland, and small patch located at the border of Picea abies woodland and raised bog. The complex includes also poor fens.
5. Litworowy Staw in Gąsienicowa Valley -rel. 5, Fig. 3E -a small patch of P. mugo shrubs on peat bog surrounded by poor fen which transits towards the reed bed of Carex rostrata, followed by the lake.
7. Smreczyński Staw -rel. 7, Fig. 3A -a patch of P. mugo shrubs on peat bogs followed by a poor fen with elements of raised bogs occur on Western side of the dystrophic lake. The thickness of peat reaches 3.9 m (Dyakowska 1932).
8. Strzelecka Koliba -rel. 8, Fig. 4B -P. mugo shrubs on peat bogs form narrow line, separating Norway spruce bog woodlands from poor fen. Furthermore, there is a small patch of raised bog in the middle of that mire.
9. Tomanowa Valley -rel. 9A-C, Figs 2F-G, 3Bcomplex of mires on a small plateau above the bottom of valley. There are two patches of P. mugo shrubs on peat bogs, separated by Norway spruce bog woodlands and fragments of raised bog transitioning towards poor fen.
10. Toporowy Staw Wyżni -rel. 10A-C, Figs 2A, 3F -dense belt of P. mugo shrubs on peat bogs encompasses from East and North poor fen with fragments of raised bog, on the Northern side dwarf pine krummholz stretches out for 50 m, bordering raised bog. From West P. mugo borders Norway spruce bog woodland. The thickness of peat reaches 4 m. There is a lens of water in the central part of the peat bog, between the layer of peat and lake sediments (Kloss 2020).
11. Waksmundzka Polana -rel. 11A-C, Fig. 4E patches of P. mugo shrubs on peat bogs are striated by the fragments of raised bog and surrounded from southeast by Norway spruce bog woodland.
12. Waksmundzka Rówień -rel. 12, Fig. 4F -scattered patches of P. mugo shrubs are located in the center of raised bog, surrounded by upper montane Norway spruce forest.
13. Wielka Pańszczycka Młaka -rel. 13A-C, Fig. 4A -in this complex of mires two patches of P. mugo shrublands occur -large patch, surrounded from southeast by Norway spruce bog woodlands and bordering from west with raised bogs, and from south with poor fen. Furthermore, there is a minor belt of P. mugo shrubs located north from the raised bog. The thickness of peat reaches 5.4 m (Obidowicz 1975).
14. Wyżnia Pańszczycka Młaka -rel. 14, Fig. 4D dwarf pine shrubs on peat bogs form narrow belt reaching poor fen which also shows some features of raised bog on the southern side. The thickness of peat reaches here 3.75 m (Obidowicz 1996).

Discussion
The floristic composition of patches of P. mugo shrubs described in this study is similar to those observed by Obidowicz (1975). The only species which were not found in 2019 were Barbilophozia florkei, Calypogea sphagnicola, Dicranum undulatum, Gymnocolea inflata and Lophozia wenzelii. However, Gymnocolea inflata occurred frequently in the neighboring peat bogs. Furthermore, Obidowicz (1975) mentioned Melampyrum sylvaticum in these shrublands, which is a mistake. This species does not grow on peat bogs, unlike similar Melampyrum pratense. According to Matuszkiewicz (2008) it is a characteristic species for the Pino mugo-Sphagnetum. Hadač et al. (1969) (Hadač et al. 1969). It is worth emphasizing that, except for Oxycoccus microcarpus, all of the above mentioned species also occur in similar shrublands in the Polish Tatras. Oxycoccus microcarpus is a rare and endangered species in the Polish Tatra National Park. Its distribution is limited to only four localities (Ociepa et al. 2020). All of them are situated in mires neighboring P. mugo shrubs on peat bogs (Polana Waksmundzka, Wyżnia Pańszczycka Młaka, Toporowy Staw Wyżni, Dolina Tomanowa). Therefore, it is possible that Oxycoccus microcarpus also grows in Polish Tatras on such shrublands, but has not been found there yet. The other difference between P. mugo shrubs growing on both sides of the national border is a lack of Picea abies in the Slovakian Tatras. This could be explained by the higher elevation of analyzed dwarf pine krummholz, located above the timberline. Furthermore, in the Slovakian Tatras grows Empetrum hermaphroditum, whereas on the Polish side Empetrum nigrum grows. This can also be explained by the altitude difference. Empetrum nigrum grows in the lower montane belt and occasionally in the upper montane zone, whereas E. hermaphroditum occurs in the subalpine and alpine zone (Combik & Mirek 2015). In addition, Sphagnum compactum frequently occurs on the Slovakian side. This species has not been detected so far in P. mugo shrubs on peat bogs in the Polish Tatras. It dominates the moss layers in the Trichophoro cespitosi-Sphagnetum compacti and Carici lachenalii-Eriophoretum vaginati associations, which occur in the High Tatras (1500-2100 m a.s.l.) (Sekulová et al. 2011).
P. mugo shrubs were usually classified in the association Pino mugo-Sphagnetum Kästn. et Flössn. 1933em. Neuh. 1969corr Dierss. 1975(Herbich et al. 2004, Matuszkiewicz 2008, Matuszkiewicz et al. 2013). According to Šibík et al. (2008), this classification is incorrect. Kästner i Flössner (1933) described an association called Pinetum uncinatae. Nauhäusl (1969) changed its name to Pino-Sphagnetum. However, this was erroneous, because the updated name cannot substitute welldefined syntaxon. Furthermore, these two associations are formed by two different species of pines (Pinus) (Šibík et al. 2008). The correct name of the P. mugo shrubs on peat bogs is Chamaemoro-Pinetum mughi (Zlatník 1928) Hadač et Váňa 1967. However, Šibík et al. (2008 proposed that Sphagno magellanici-Pinetum mugo Hadač, Ježek et Březina 1969 should be treated as a correct name -nomina conservanda, due to the fact, that eponymous species Rubus chamaemorus does not occur within the entire range of distribution of P. mugo shrubs on peat bogs. P. mugo shrubs on peat bogs in Sudetes have similar species composition as in the Tatras (Żołnierz et al. 2012). However, Rubus chamaemorus does not occur in the Tatra Mountains. Presence of this species was the reason to treat P. mugo shrubs on peat bogs as a separate association, Chamaemoro-Pinetum mughi (Zlatník 1928) Hadač et Váňa 1967(Kwiatkowski 2007. Such concept is not accepted by Šibík et al. (2008), who treat P. mugo shrubs on peat bogs in the Sudetes and Carpathians as one plant association, Sphagno magellanici-Pinetum mugo, common to both mountain ranges.
Another important and disputed issue is an affiliation of P. mugo shrubs to the certain syntaxonomic class. Diagnostic species of this association belong either to the class of peat bogs vegetation Oxycocco-Sphagnetea Br.-Bl. et Tx. 1943, or coniferous forests Vaccinio-Piceeteta Br.-Bl. 1939. According to some authors, Sphagno magellanici -Pinetum mugo should be classified to the Oxycocco-Sphagnetea class (Hadač & Váňa 1967, Hadač et al. 1969, Potocka 1996, Soltes et al. 2001, Matuszkiewicz 2008, Herbich et al. 2004, Matuszkiewicz 2013, whereas others (for example Seibert 1992) claim that such vegetation belongs to Vaccinio-Piceetea. Šibík et al. (2008) suggest another solution and includes that association to Vaccinio uliginosi-Pinetea sylvestris Passarge 1968. This class encompasses azonal, oligotrophic coniferous tree-and shrub-communities, more or less peaty, in the boreal and mountain region (Šibík et al. 2008) Concluding, P. mugo shrubs on peat bogs in the Polish Tatra National Park occur on a relatively small area. They should be classified according to Šibík et al. (2008) as Sphagno magellanici-Pinetum mugo. These shrublands are similar to those growing on the Slovakian side of the Tatras.