This region is conventionally bounded on the west and on the east by valleys of the Oder River and the Vistula River. The Baltic Sea coastline constitutes its northern border, while the southern border is delineated by the S line of maximal extent of Vistulian/Würm glaciation marked by marginal landforms of the Leszno Phase (Kondracki 2011, Solon et al. 2018). However, in practice, regions of the Po-merania Lakelands are the most important. In particular, river valleys, primarily formed in the deglaciation process, and depressions of different origin, most often with lakes currently at different stages of terrestrialization, played a significant role in the development of alkaline fens. Variable geological landforms dominated by moraine glacial till and sorted sands and gravels of sandurs are essential for the chemical character and composition of groundwater supporting the fens (Herbich 1994, Wołejko 2000, Osadowski 2010).
In terms of the administrative division of Poland, this area occupies the Zachodniopomorskie Voivodeship and parts of the Pomorskie Voivodeship and Kujawsko-Pomorskie Voivodeship located west of the Vistula River and northern parts of the Lubuskie Voivodeship and Wielkopolskie Voivodeship. According to data from the Naturalists’ Club database, 235 patches of habitat 7230 in this region cover an area of ca. 1450 ha in total. Several distinct areas of alkaline fen concentration can be distinguished. They are situated in the following mesore-gions (Kondracki 2011, Solon et al. 2018): Białogard Plain, Słupsk Plain, Polanów Heights, Choszczno Lakeland, Drawsko Lakeland, Bytów Lakeland, Cassubian Lakeland, Gorzów Plain, Drawa Plain, Wałcz Lakeland, Szczecinek Lakeland, Gwda river valley, Southern Krajna Lakeland, Charzykowy Plain and in the Tu-chola Forest. A few but important sites were preserved in the Lubuskie Lakeland, especially in the Torzym Plain. Several fens have also been recorded in the To-ruń-Eberswalde Ice Marginal Valley.
Alkaline fens in the northern part of the Tuchola Forest
Robert Stańko The Tuchola Forest is an expanse of large sandur plains having an area of over 3 000 km2 covered by a complex of oligotrophic pine forests, one of the largest in
western Poland, situated in two mesoregions: the Charzykowy Plain and the Tucho-la Forest. These are terrains with reTucho-latively diverse young-gTucho-lacial Tucho-landforms, inter-woven by well-developed hydrographic grid and numerous water bodies, including many hard-water lakes dominated by Chara spp. More than 50 alkaline fens have been reported to be located mostly in the northern part of the complex.
Alkaline fens are encountered here most often in the vicinity of the lakes lo-cated in vast, relatively shallow kettle depressions and also in narrow deep sub-glacial tunnel valleys. Diverse, concave landforms usually filled with sediments are the primary basis for development of alkaline fens gaining over time also hy-drological support from groundwater. The hyhy-drological relations of this area are determined by special geomorphological configuration. Waters supplying the al-kaline fens originate from vast sand outwash plain. Usually they form one main water-bearing horizon, while in the tunnel valleys located in the neighboring Cas-subian Lakeland, several inter-moraine horizons are present (Herbich 1998a).
It is also noteworthy that carbonate formations are locally exposed, as near the source of the Kulawa river where alkaline mires are located in a nature reserve Dolina Kulawy established, among others, for their conservation (see Chapter 8).
The geological structure of this river valley is partially associated with a broken natural barrier maintaining an earlier water level in postglacial reservoirs. In a part of the valley, erosion processes have uncovered the layers of calcareous gyt-tja and carbonate tufa (of spring origin) lining bottoms of old reservoirs and the seeping edges of river valleys (Prusinkiewicz & Noryśkiewicz 1975). Apart from alkaline mires, the localities of many calciphilous mesophilic species can be iden-tified in this area. Small patches of interesting calciphilous vegetation regenerate also at locations of former excavation works, like in the former chalk mine near Zapceń village.
This area is distinguished by the highest concentration of sedge-moss fens in all of northwestern Poland (ca. 7,5 fen/100km2) and by the best conserva-tion status and diversity of flora, especially in the fens located close to the lakes since they were not so easy to dewater. Special geomorphological features (bio-gene-poor sandur landscape, less suitable for agricultural use but rich in calci-um carbonate limiting natural and anthropogenic eutrophication processes) and probably historical factors enabled the survival here of the several best developed and conserved sites in the western Poland. The following are worth mentioning:
Mechowisko Radość, Bagno Stawek, Krąg lake, Księże lake, Kruszynek, Zielona Chocina, Polgoszcz, Wieck, Zdrójno, Cypel, Kulawa river valley, Lipczynka river valley, and Dłużnica river valley. Most of these mires developed as a result of lake terrestrialization which is confirmed by their shallow peat beds directly overly-ing, mostly carbonate, gyttjas. It is also worth noting that these mires have huge potential for further stable development and expansion in size due to constant overgrowing of adjacent water bodies.
The vegetation of the alkaline fens in this area is often presented as a reference for sedge-fens of northwestern Poland while these sites are mentioned among the most dazzling natural sites (Stańko & Wołejko 2018a). At the best preserved sites, for example Bagno Stawek or Mechowisko Radość, relative large areas are occupied by already exceptionally rare in lowlands associations: Eleocharitetum pauciflorae, Caricetum paniceo-lepidocarpae and Scorpidio-Caricetum diandrae.
The mosaic of moss-low-sedge vegetation is complemented by the most common of lowland sedge-moss associations, namely Menyantho-Sphagnetum teretis. All the aforementioned associations are distinguished by the highest concentration of species in this part of Poland considered to be characteristic of the Caricion daval-lianae alliance and exceptionally rare species. Alkaline fens of the northern part of the Tuchola Forest are the largest refuge of Saxifraga hirculus in western Poland. In addition, these areas harbor probably the most abundant populations in western Poland of such species as: Liparis loeselii, Carex dioca, C. chordorrhiza, mosses:
Cinclidium stygium, Hamatocaulis vernicosus, Scorpidium scorpioides, Limprich-tia cossonii, Tomentypnum nitens, Helodium blandowii, Paludella squarrosa and species of the genus Campylium spp. Rarities of this area also include species oc-curring sporadically and increasingly rarely recorded in Poland: Pseudocaliergon trifarium and Meesia triquetra. Sedge-moss fens are also overgrown by character-istic peat mosses: Sphagnum warnstorfii, Sph. subnitens and Sph. teres. A majority of fens harbor abundant orchid populations: Dactylorhiza majalis, D. incarnata, D. fuchsii and the most abundant Epipactis palustris. Low sedge vegetation and excellent water conditions of the best preserved fens (valleys) provide favourable conditions for growth of bladderworts including Utricularia australis, U. inter-media, U. minor, U. ochroleuca.
Some sites located in this area have been long known and are thoroughly de-scribed in scientific literature, e.g., Bagno Stawek (Lisowski et al. 1965), however the majority of them have been identified and described in recent years (Gdaniec 2010, Gdaniec & Markowski 2010, Gdaniec & Schutz 2010, Stańko et al. 2015, Kozub & Dembicz 2018). Mechowisko Radość, adjacent to the Luboń village, can be mentioned here as a specific case as it was discovered in 2008 and first de-scribed as late as in 2009 as one of the most valuable alkaline fens in western Poland (Kujawa-Pawlaczyk et al. 2009, Stańko et al. 2015).
Observations and surveys carried out in recent years indicate that other still unknown alkaline fens can be discovered in this area.
Knowledge on the alkaline fens in the Tuchola Forest was significantly ex-tended and updated during documentation of valuable fens and drafting projects of their conservation realized by the Naturalists’ Club and Regional Directorate of Environmental Protection (RDOŚ) in Gdańsk in recent years. A synthetic de-scription of the natural conditions of the most important sites and references to
Photo 82: Mechowisko Radość nature reserve of terrestrialization origin, is a locality of yellow marsh saxifrage (photo by J. Kujawa-Pawlaczyk).
unpublished materials can be found in the following publications: Kiaszewicz &
Stańko (2011a), Wołejko et al. (2012), Stańko & Wołejko (2018a).
The alkaline fens of this area are protected in Natura 2000 sites:
Sandr Brdy PLH220026, Ostoja Zapceńska PLH220057, Jezioro Krąg PLH220070, Jezioro Księże w Lipuszu PLH220104, Rynna Dłużnicy PLH220081 and Jeziora Wdzydzkie PLH220034; while those located at the site Nowa Brda PLH220078 still require inclusion in the list of protected sites (see Chapter 8). Until the end of the last century, only one nature reserve protecting alkaline fens was established there, i.e., Bagno Stawek, created in 1977. The Dolina Kulawy nature reserve was established in 2009 (enlarged in 2009) while the next nature reserves created in the period 2014 – 2018 most of all to protect alkaline fens include: Mechowisko Radość, Kruszynek and Mechowisko Krąg covering a total area of ca. 22 ha (Ma-kowska et al. 2018). Their management was planned in parallel (Re(Ma-kowska et al.
2014, Bociąg et al. 2014, Gawroński et al. 2016). It is still necessary to establish the Zdrójno nature reserve and Jezioro Trawnickie nature reserve and to perform corrections of boundaries of Natura 2000 sites (see Chapter 8).
Alkaline fens in the Kaszuby moraine landscape
Robert Stańko, Paweł Pawlaczyk A concentration of alkaline fens is situated in three mesoregions: the Cassu-bian Lakeland and the Żarnowiec Height split by the Reda-Łeba Progracial Val-ley. The moraine part of the Kaszuby region, unlike the adjacent sandur areas, is characterized by the presence of a few scattered alkaline fens, most of which are in bad shape.
On the slope of Żarnowiec Height and on the bank of Reda-Łeba Progracial Valley, Orle mire is located. Alkaline fens have been preserved here in the edge mineral zone of a very large wetland complex surrounding the lake. They origi-nated from lake terrestrialization but at present they are situated 1 – 1,5 m above the water level; they are supplied by groundwater flowing from the northern and northeastern edge of the Żarnowiec Heights. Habitat 7230 at this location covers a coherent area of ca. 36 ha, which is rather exceptional in western Poland, and is characterized by the occurrence of an almost complete set of regional typical species, e.g., Liparis loeselii, Dactylorhiza fuchsii, D. incarnata, D. maculata, D.
majalis, Epipactis palustris, Polemonium coeruleum and bryophytes: Paludella squarrosa, Helodium blandowii, Tomentypnum nitens and Hamatocaulis verni-cosus.
The fen is overgrown by vast patches of blunt-flowered rush Juncus subnodu-losus, the population of which belongs to the largest in this region. Unfortunately, almost all resources of well-preserved alkaline fens are privately owned and the owners do not agree to the implementation of necessary conservation measures (Stańko 2011).
The sedge moss fen at the Bukowina River mouth to the Kamienieckie lake in the Sierakowice municipality is long known (Herbich 1994) and given the sig-nifying name of either Jezioro Święte or Jezioro Kamienieckie. The mire fills the terrestrialized bay of this lake. The dominant communities include the Menyan-tho-Sphagnetum teretis and the Caricetum diandrae, harboring, e.g., Helodium blandowii, Tomentypnum nitens and numerous orchids Dactylorhiza spp. (Utrac-ka-Minko, unpublished).
The alkaline fen located in the area of the Zęblewo village in the Szemud mu-nicipality is now occupied predominantly by meadows where only four patches of typical vegetation (Menyantho-Sphagnetum teretis, sedge-moss fen form of the Caricetum rostratae) were preserved and called the Mechowiska Zęblewskie. This habitat developed into several small patches in the edge zone of a small stream valley. The central part of this area is covered by heavily flooded rushes, mostly reeds and tall sedges, surrounding a few ponds created probably by beaver dams.
The plant communities representing the habitat are characterized by a significant proportion of meadow species, which are now heavily saturated with water due to beaver activity. In spite of this, they are increasingly overgrown by willows and black alders.
The fen developed as a result of lake terrestrialization processes. Drilling showed a shallow sedge-moss peat layer (to a depth of 40 cm) underlain by or-ganic gyttja.
Several alkaline fens are concentrated in the Ostrzyca Tunnel Valley in the Stężyca municipality. In the past, sedge-moss fens were reported to be situated in a narrow strip of land between the Lubowisko lake and Dąbrowskie lake (Her-bich 1994) and at the edge of the Potulskie ribbon lake near the Gołubie village.
At the latter site, even today the Menyantho-Sphagnetum teretis was confirmed with abundant population of the marsh helleborine Epipactis palustris. The most interesting site, i.e., Gołubie mire located in the side tunnel valley south of the Dąbrowskie Lake is overgrown by a mosaic of communities: Scorpidio-Carice-tum diandrae, CariceScorpidio-Carice-tum lepidocarpae and Menyantho-SphagneScorpidio-Carice-tum teretis, with a well-developed brown moss layer comprising Paludella squarossa, Tomentyp-num nitens and Helodium blandowii, with a locality for Liparis loeselii (Utrac-ka-Minko, unpublished).
Several small alkaline fens can be found in the western part of this area at the upper Łupawa river and its tributary – the Bukowina river. The sites on the Bukowina river are heavily degraded but the interesting Dąbie fen was preserved along a short Łupawa tributary west of the Rokitki village. It is covered by a
com-Photo 83: Dąbie fen in the Łupawa river valley (photo by J. Kujawa-Pawlaczyk).
plex of communities Menyantho-Sphagnetum teretis, Caricetum appropinquatae and Scorpidio-Caricetum diandrae with carpets of moss Helodium blandowii and Cinclidium stygium; orchids are very abundant: Epipactis palustris, Dactylorhiza incarnata, D. majalis, D. fuchsii (Kujawa-Pawlaczyk, unpublished).
The fen in the southern part of this area in the Wierzyca river valley north of the Wielki Klincz village is strongly degraded and practically transformed into a wet meadow, but it is known as a site where interesting studies were conducted to determine the effect of mowing on alkaline fen vegetation (Kozub et al. 2019).
Alkaline fens in the Upper Słupia River catchment area
Robert Stańko This complex of alkaline fens is located in the western parts of the mesore-gions: Bytów Lakeland and Polanów Heights. The landscape is dominated by mo-raine high plains with relatively numerous lakes in tunnel valleys. The Słupia Riv-er with plentiful small tributaries is the main axis of this area.
Alkaline mires in the Upper Słupia river catchment area occupy both terres-trialized lake basins (with dominating percolating water supply) and the edges of river valleys where the water supply from springs prevails. They widely differ in hydrological relations which is associated with peculiar geomorphological fea-tures of their groundwater catchment area. Waters supporting alkaline fens can originate both from one water-bearing horizon (sites located in close proximity or on vast sandur plains) and from many water-bearing layers in the case of tunnel valleys cracking through moraine landforms.
The distribution and natural values of the fens in this area are well recog-nized. It was possible owning to realization of the project “Valorization of natu-ral resources and preliminary characterization of hydroecological conditions of wetland ecosystems in the Słupia River Valley Landscape Park” carried out by the Landscape Park in 2001 – 2002 (Stańko et al. 2002, in Polish).
To date, a dozen or so sites of different sizes have been preserved in this area;
they are usually in bad shape due to draining and transformation into meadows and pastures. Also a lot of hydrotechnical transformations, like the construction of watermills and small hydropower plants either on the Słupia river of its tribu-taries, have contributed to fen degradation. A hydropower plant system and re-lated historical infrastructure have been in operation until today to the detriment of the alkaline fens. It is harmful for spring fens situated along the so-called Old Słupia river, i.e., the original river-bed, presently carrying only a slight amount of water. The remaining water flow was diverted to the new river channel, several kilometers long, to supply the hydropower plant.
Consequently, characteristic vegetation of alkaline fens, especially typical sedge-moss fens, has been preserved in a residual form. The only exemption is a remarkably well-preserved fen in the Mechowiska Sulęczyńskie nature reserve (Herbichowa & Herbich 2015, Herbich 2017). It is a very young terrestrialized mire on deep calcareous gyttja bed with a few traces of exploitation. Its most im-portant floristic components include such species as the Liparis loeselii, Ham-marbya paludosa, Carex dioica, Stellaria crassifolia and rare in the northern part of the country Eriophorum latifolium. Moreover, orchid species have developed there very large populations comprising thousands of individuals: Epipactis palus-tris while Dactylorhiza majalis and D. incarnata are less abundant. Of the bry-ophytes, the following are worth mentioning: Cinclidium stygium, Hamatocaulis vernicosus, Scorpidium scorpioides and huge populations of Paludella squarrosa, Tomentypnum nitens and Helodium blandowii.
The nature reserve, postulated for several years, was established as late as in 2014, among other things thanks to a land purchase by the Naturalists’ Club. Al-most immediately thereafter, a conservation plan for this area was prepared and a thorough scientific monograph was published (Herbich 2017), concluding many years of interdisciplinary studies.
Among the terrestrialization mires of the Upper Słupia river catchment area, also two other sites protected as nature reserves – Gogolewko and Skotawskie Łąki – are worthy of notice. These sites were heavily transformed in the past. Al-though the major part of their area was changed into meadows, they have been undergoing slow spontaneous renaturation and regeneration as a result of imple-mentation of conservation measures (blockading of ditches and restoration of ex-tensive mowing). The characteristic vegetation of alkaline fens was preserved only in small and scanty patches (e.g., an excellently preserved Scorpidio-Caricetum di-andrae patch of several ares with copious appearance of Hamatocaulis vernicosus in the Skotawskie Łąki nature reserve), but these sites are interesting as examples of spontaneous renaturation processes.
The Gogolewko nature reserve was probably the first where an example of spontaneous sedge-moss fen regeneration in shallow peat hollows was described (Stańko et al. 2003). This process has been observed already for over ten years and the vegetation identified in 2001 still preserves its character.
The Mechowiska Czaple nature reserve is a representative of the second group of alkaline fens of the Upper Słupia River catchment area, formerly more wide-spread, developing in systems of transverse river valleys. In the past almost the entire side valley of a tributary of the Słupia river was covered by alkaline fens.
On the steepest edges, typical spring fens including cupola springs developed, of-ten transforming into percolating fens in the lowest parts of the valley. A part of the mires was irreversibly transformed into meadows. However, those receiving ample groundwater supply, survived. The vegetation is diverse; vegetation of the cupola springs heavily saturated with water is dominated by lesser pond sedge
Carex acutiformis with copious representation of Equisetum fluviatile and E.
palustre. In the neighborhood, shallow peats (ca. 30 – 40 cm deep) are also cov-ered by typical sedge-moss fen vegetation represented by the Menyantho-Spa-hagnetum teretis association. The conducted stratygraphic studies confirmed the presence of moss and sedge-moss peats with tufa interbeddings in the central part of the valley.
Small but valuable alkaline spring fens are also preserved along the Słupia River near the Parchów village. Unfortunately, floristic elements characteristic of sedge-moss vegetation are scanty, but an abundance of orchids is a hallmark of these sites. In respect of landscape, the cupola fens of the so-called Old Słupia
Small but valuable alkaline spring fens are also preserved along the Słupia River near the Parchów village. Unfortunately, floristic elements characteristic of sedge-moss vegetation are scanty, but an abundance of orchids is a hallmark of these sites. In respect of landscape, the cupola fens of the so-called Old Słupia