Plant communities specific for alkaline fens

The vegetation cover of alkaline fens can be built by very different plant com-munities (see wider discussion of the possible vegetation of this type of habitat in Stańko et al. 2018). However, several plant associations are specific to this ecosys-tem. These associations were included by most authors in two orders: Caricetalia davallianae and Scheuchzerietalia palustris. The first order includes the Caricion davallianae alliance, as well as the recently distinguished Sphagno warnstor-fiani-Tomenthypnion alliance (Hájek et al. 2006, Šefferová-Stanová et al. 2008).

Plant associations from these orders are key components of the vegetation of some alkaline wetlands, and some of them exhibit a close (or sometimes even exclusive) relationship with these ecosystems. Related carbonate ecosystems are petrifying -, calcarous - and alkaline fen types.

The vegetation belonging to the Caricetalia davallianae order has been the subject of many publications. In the mountain and upland areas vegatation of alkaline fens consists of the following plant associations: Valeriano-Cari-cetum flavae, CariValeriano-Cari-cetum davallianae, Ctenidio mollusci-Seslerietum uliginosae, Lipario-Schoenetum ferruginei and Sphagno warnstorfiani-Eriophoretum latifolii (e.g., Fijałkowski 1959, Pawłowski et al. 1960, Kornaś & Medwecka-Kornaś 1967, Stuchlikowa 1967, Hereźniak 1972, Grodzińska 1975, Jargiełło 1976, Głazek 1984, 1992, Fijałkowski & Chojnacka-Fijałkowska 1990, Pisarek 1996, Hájek 1999, Jutrzenka-Trzebiatowski & Szarejko 2001, Towpasz & Stachurska-Swakoń 2009 and Koczur & Nicia 2013). A more complete review of the literature sources, in-cluding unpublished materials, can be found in the monograph of Vončina (2017).

From the fens found in the lowland situated in the northern and north-west-ern part of Poland, the following associations have been reported: Eleocharitetum pauciflorae (=Eleocharitetum quinqueflorae), Campylio-Caricetum dioicae, Carice-tum paniceo-lepidocarpae, JunceCarice-tum subnodulosi, Orchido-SchoeneCarice-tum nigricantis, Campylio-Trichophoretum alpini, Helodium blandowii-Carex acutiformis commu-nity, Carex buxbaumii commucommu-nity, Schoenus ferrugineus community and many others (Steffen 1931, Kaczmarek 1960, 1962, Jasnowski 1962, Pałczyński 1975, Głowacki & Wilczyńska 1979, Jasnowska & Jasnowski 1983, Herbich & Herbicho-wa 1984, Sokołowski 1986-1987, 1988, 1996, Tyszkowski 1993, Kucharski 1998, Kwiatkowski 1999, Wołejko 2000b, Wojterska et al. 2001, Pawlikowski 2000, Her-bich 2017).

Photo 22: Menyantho-Sphagnetum teretis (photo by R. Stańko).

Photo 23: Eleocharitetum pauciflorae (=Eleocharitetum quinqueflorae) (photo by R. Stańko).

The order Scheuchzerietalia palustris essentially consists of plant associations typical of other peatland habitats (such as sub-neutral and transitional mires).

However, for northern Poland in particular, two additional associations have been included in this order, i.e., Menyantho-Sphagnetum teretis and Scorpidio-Cari-cetum diandrae (= CariScorpidio-Cari-cetum diandrae), constituting the dominant element of undrained alkaline fens, classified as habitat type 7230, as defined in Chapter 1.

Within these phytocoenoses, peatland species with a wider ecological amplitude are supplemented by less numerous species characteristic of the Caricion davalli-anae alliance.

Figures 22-31 show the most recent distribution of the most important indi-cator associations for alkaline fens in Poland. The source of this information is the updated database on alkaline fens, available at the webpage of the Naturalists Club. The dissemination image was supplemented with verified phytosociological data from scientific publications. The nomenclature of the associations follows Ratyńska et al. (2010).

In the light of new knowledge (Peterka et al. 2017), the inclusion of some of these associations in higher syntaxonomic units (especially in the rank of alli-ance) needs revision. This applies mostly to associations previously included in the Caricion lasiocarpae alliance. As a result of the recent analysis of abundant phytosociological records from Europe, vegetation of fen and transitional mires has been regrouped into 13 units in the rank of alliance (Peterka et al. 2017). In view of this new classification, the vegetation of the best preserved Polish alkaline fens contains floristic elements representing mainly 4 vegetation alliances: Cari-cion davallianae Klika 1934, Stygio-CariCari-cion limosae Nordhagen 1943, Sphagno warnstorfii-Tomentypnion nitentis Dahl 1956 and Saxifrago-Tomentypnion Lap-shina 2010, which partly have different geographical ranges (Fig. 21).

Fig. 21. Distribution of four natural alkaline fen communities (in the rank of alliance) in Europe (Peterka et al. 2017).

Caricion davallianae Sphagno-Tomentypnion Stygio-Caricion limosae Saxiftrago-Tomentypnion

The Caricion davallianae alliance includes the vegetation of petrifying spring and alkaline fens supplied with calcareous groundwater. The dominating species in the herbaceous layer are mainly calcitrophic sedge plants (including Carex dav-alliana, Carex hostiana, Eleocharis quinqueflora, Eriophorum latifolium, Schoenus ferrugineus) and herbs, such as Parnassia palustris, Pinguicula vulgaris, Primula farinosa and Tofieldia calyculata. In the layer of bryophytes, there is Campylium stellatum s.l., Limprichtia cossonii, Palustriella commutata s.l. and Philonotis cal-carea. Caricion davallianae phytocoenoses are widespread in Europe, but the

Fig. 22. Distribution of the

Valeriano-Caricetum flavae. Fig. 23. Distribution of the Caricetum davallianae.

Photo 24: Caricetum davallianae (photo by R. Stańko).

Photo 25: Valeriano-Caricetum flavae (photo by D.Horabik).

centers of their occurrence are situated in the Alps and the Carpathians. In Po-land some of these species are currently extremely rare. An examples is Primula farinosa with only one site. In Poland, associations belonging to the Caricion davallianae alliance are best developed within the alkaline flush fens. The Valeri-ano-Caricetum flavae association Pawłowski 1949 ex 1960 is present almost exclu-sively (but frequently) in the mountains and foothills. The second of the frequent associations – Caricetum davallianae Dutoit 1924 – has a wider range and can be found throughout southern Poland.

Two other associations belonging to the Caricion davallianae alliance are the Ctenidio mollusci-Seslerietum uliginosae Klika 1943 em. Głazek 1984 and the Schoenetum ferruginei Du Rietz 1925, which are both concentrated in specific regions of Poland only (Fig. 24 and Fig. 25). The Ctenidio mollusci-Seslerietum uliginosae has a very limited distribution and is almost exclusively found in the Nida Basin and in the Świętokrzyskie Mountains. The occurrence of Schoenetum ferruginei is mainly limited to south-eastern Poland, where it is a component of alkaline fen developed in the complex of specific calcareous mires, that have been formed on top of the chalk deposits (Buczek & Buczek 1993, see also chapter 7.2).

Fig. 24. Distribution of the

Schoenetum ferruginei. Fig. 25. Distribution of the Ctenidio mollusci-Seslerietum uliginosae.

Photo 26: Schoenetum ferruginei on the dome of a spring fen with travertine deposits (Śniatycze-Komarów near Zamość) with a large share of Swertia perennis and Molinia

caerulea. In the background, the Cladietum marisci association covering the top of the cupola (photo by D. Horabik).

The association Caricetum paniceo-lepidocarpae (Steffen 1931) W. Braun 1968 occurs all over the country, but is the most frequent Caricion davallianae associ-ation of the north-eastern Poland. The rarer, pioneer community Eleocharitetum pauciflorae Lüdi 1921 also has a wide distribution pattern in Poland.

The Juncetum subnodulosi (Allorge 1922) W. Koch 1926 association is restrict-ed to north-western Poland, which is probably relatrestrict-ed to the sub-Atlantic charac-ter of Juncus subnodulosus (Markowski & Stasiak 1988).

Photo 27: Caricetum paniceo-lepidocarpae (photo by R. Stańko).

Photo 28: Juncetum subnodulosi (photo by R. Stańko).

Fig. 27. Distribution of the Eleocharitetum pauciflorae.

Fig. 26. Distribution of the Caricetum paniceo-lepidocarpae.

Fig. 28. Distribution of the Juncetum subnodulosi.

The alliance of Sphagno warnstorfii-Tomentypnion nitentis is characterized by the presence of calcium-tolerant Sphagnum mosses (such as Sphagnum contor-tum, Sphagnum subnitens, Sphagnum teres and Sphagnum warnstorfii) and also by brown mosses occupying higher positions in microtopography (e.g., Aulacomni-um palustre, Paludella squarrosa and TomentypnAulacomni-um nitens). Typical species of al-kaline fens are also numerous here: Campylium stellatum s.l., Limprichtia revolvens agg., Carex davalliana, Eleocharis quinqueflora, Eriophorum latifolium, Parnassia palustris etc. Acidophilous plants with shallow roots (e.g., Drosera rotundifolia) can be found on elevated hummocks formed by bryophytes, constituting favour-able conditions. The large diversity of micro-habitats causes the mire vegetation of this alliance to be one of the richest in floristic terms. It is spread throughout Europe, but more often found in mountainous and upland areas. Also in Poland,

the generally rare localities of the communities belonging to the alliance have been mainly found in mountainous and sub-mountainous areas: in the Carpathi-ans (Hájek 1999), the Sudety Mountains (e.g., Orlicke Mountains: Smoczyk &

Karakula 2016), and even within the limits of Kraków municipality– as a Sphagno warnstorfii-Eriophoretum latifolii association, Rybníček 1974 (Koczur 2014).

Proposals to include some phytocenoses of alkaline fens of northern Poland in the Sphagno warnstorfii-Tomentypnion alliance, require a critical analysis. In the light of available phytosociological records, the floristic affinities of the pre-viously recognized communities from the Sphagno warnstorfii-Tomentypnion al-liance with the flush fen associations Valeriano-Caricetum flavae and Caricetum davallianae are visible.

Fig. 29. Distribution of the Sphagno warnstorfii-Tomentypnion nitentis.

Phytocoenoses belonging to the Stygio-Caricion limosae alliance are often found in strongly hydrated peatlands with a topogenic water supply type. The veg-etation consists of small sedges (e.g., Carex chordorrhiza, Carex lasiocarpa, Carex limosa) and brown mosses forming loose turfs (e.g., Pseudocalliergon trifarium, Scorpidium scorpioides) and a few Sphagnum mosses (e.g., Sphagnum contortum and Sphagnum platyphyllum). The communities of this alliance are widespread in northern Europe, reaching southward to the British Isles and Ireland and north-eastward to the Baltic Republics. It is also found in the Alps and, less often, in the Carpathians and the Balkans. Many of the foregoing species are floristic pe-culiarities in Poland, found mainly on the best-preserved alkaline and subneutrial fens of northern Poland. To date, no specific plant associations have been assigned to this alliance. Initial vegetation analysis carried out for the purpose of this study suggests that it should include the most-common Polish sedge-moss associations, especially those occurring in the north of the country: Menyantho-Sphagnetum

teretis Warén 1926 and Scorpidio-Caricetum diandrae Osvald 1926 nom. inverse.

et nom. mut. Until now, these associations were most often included in the alli-ance Caricion lasiocarpae Vanden Berghen in Lebrun et al. 1949 or Caricion ni-grae, however the legitimacy of distinguishing this first alliance is currently being questioned (Peterka et al. 2017).

Fig. 30. Distribution of the

Menyantho-Sphagnetum teretis. Fig. 31. Distribution of the Scorpidio-Caricetum diandrae.

The Saxifrago-Tomentypnion alliance includes fens rich in calcium (but no accumulation of calcareous tufas). In addition to species typical of the alkaline fen plants described above, there are bryophyte species with higher trophic re-quirements. These are wetland species with a wider ecological spectrum (such as Brachythecium mildeanum, Drepanocladus aduncus agg., Marchantia polymor-pha) or specialized brown mosses with a higher demand for phosphorus (such as Hamatocaulis vernicosus; c.f., Hájek et al. 2014). A characteristic feature of the herbaceous layer is the coexistence of marsh and water plants (Cicuta virosa, Ranunculus lingua, Thelypteris palustris), meadow species (such as Poa pratensis agg., Rumex acetosa s.l.), and sometimes rare species of nutrient-poor boreo-con-tinental habitats (Saxifraga hirculus, Stellaria crassifolia, Triglochin maritima). The alliance, originally described from western Siberia, occurs in the north-eastern part of the European Lowlands and in isolated positions of the Romanian Car-pathians. It was also found at several positions in Germany (Peterka et al. 2017).

Within Poland, most of the sites with the vegetation of this alliance is probably related to the presence of specific subneutral mires, which are frequent in the Su-wałki Lake District (Pawlikowski et al. 2013).

It is worth noting that all plant associations specific for alkaline fens are rare or very rare in Poland, and their threat condition is defined as “directly threatened with extinction” or “vulnerable” (Ratyńska et al. 2010).