Meadows with dandelions of the section Palustria in Pogórze Dynowskie , S Poland

The paper presents ecological characteristics of meadows with Taraxacum sect. Palustria in Pogórze Dynowskie. Field studies were carried out using the patrol method. Floristic description was made, methods of meadow use were evaluated and habitat conditions were determined based on Ellenberg’s bioindication method on every meadow with marsh dandelions. Analyses were performed in eight sites with T. mendax, T. paucilobum, T. polonicum, T. portentosum, and T. vindobonense.


Introduction
Species of the genus Taraxacum attributed to the section Palustria are the plants associated with wet, extensively used meadows and pastures.They mainly form communities of the Calthion, Alopecurion, and Molinion alliances, class Molinio-Arrhenatheretea, and communities of the class Scheuchzerio-Caricetea nigrae [1][2][3][4].A few sites of dandelions of this group spread all over the country have been recorded in Poland till now [4,5].Most Polish marsh dandelions are threatened with extinction due to unfavorable changes in habitat conditions and the disappearance of appropriate phytocoenoses in many places [4].These species are also considered endangered and are listed in the "Red list of vascular plants in the Czech Republic" [6].In the opinion of the authors of the monograph on the section Palustria [2], the problem of habitat disappearance pertains to all species in the whole range of their occurrence.
From among 24 species of Taraxacum sect.Palustria found in Poland [4,7], Pogórze Dynowskie hosts seven of them.In this study, we consider six species, the seventh -T.zajacii -is a subject of a separate study [8].Five species, namely T. mendax, T. paucilobum, T. polonicum, T. portentosum, and T. vindobonense, were found in well-preserved wet meadows.Taraxacum hollandicum was, however, found in a small patch of drying meadow at the edge of shrubs with Alnus glutinosa.

Material and methods
The studies on dandelions of the section Palustria were carried out in Pogórze Dynowskie within the borders drawn by Balon et al. [9].In April 2014, all potential habitats for marsh dandelions were examined.Well-preserved meadows with marsh dandelions were found mainly in the valleys of two rivers: the Strug and the Stobnica (Fig. 1).

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The meadows were located in the ATPOL grid (2 × 2 km) [10].Sites found in the previous years listed in the paper by Marciniuk [4] were also included.Floristic lists made in the observed meadows were then arranged in a working table.Based on the table, plant species co-occurring with marsh dandelions and species that migrate to these types of meadows from neighboring habitats or have a broader spectrum of occurrence were selected.Information on the effect of meadow use on the density of dandelion populations was also recorded in the field.Habitats were evaluated with the use of indicator numbers of Ellenberg et al. [11].Nomenclature of the vascular plants follows Mirek et al. [12].Syntaxonomic affiliation was adopted after Matuszkiewicz [13].

Results
The presence of dandelions of the section Palustria in Pogórze Dynowskie is limited to wet meadows located in 12 units of the ATPOL cartogram 2 × 2 km (Fig. 2).Plant patches referred in their physiognomy and species composition to the communities of Alopecuretum pratensis, Cirsietum rivularis, or Scirpetum sylvatici.In the prevailing number of cases, these were mown meadows.In total, 102 species of vascular plants were noted in these meadows (Tab.1).Two species characteristic for the class Molinio-Arrhenatheretea, namely Cardamine pratensis and Cerastium holosteoides, were always present there.Almost at each locality we noted the species characteristic for Calthion (Cirsium rivulare, Equisetum palustre, and Scirpus sylvaticus), Cynosurion (Trifolium repens), and meadow species of a broad range of occurrence (Ranunculus acris, Rumex acetosa, and Plantago lanceolata).Less numerous and definitely less frequent were the species characteristic for various syntaxa of wet meadows (e.g., Myosotis palustris, Filipendula ulmaria, Juncus effusus, Angelica sylvestris, Lychnis flos-cuculi) or rare in Poland like Taraxacum gelertii belonging to the section Celtica.The presence of species characteristic for other syntaxonomic groups might be associated with their penetration from neighboring patches (e.g., Agrostis stolonifera, Juncus inflexus, Galium palustre, or Carex nigra) or with immigration from plant communities of quite different character (e.g., Glechoma hederacea, Urtica dioica, Ficaria verna, or Anemone ranunculoides).Noteworthy was the presence of dandelions of the section Ruderalia in floristic composition of the studied meadows.Despite rather low abundance, their list includes 27 species, some of which (T. ancistrolobum, T. lucidum, T. oblongatum, T. sinuatum, and Fig. 2 Location of the sites of dandelions of the section Palustria on cartogram maps of Pogórze Dynowskie.
Tab. 1 The species composition of meadows with the participation of Taraxacum sect.Palustria.

Discussion
Plant communities with naturally occurring marsh dandelion are primarily hay meadows from which hay has been collected.The marsh dandelion population considerably decreased, and some species, observed in the previous vegetation seasons, even disappeared on the meadows which were not used or where the mown plants where left.This shows that these plants have low resistance to changes in habitat conditions.The disappearance of marsh dandelion was primarily determined by its low competitiveness (2)(3)(4).Marsh dandelion lost the competition with high meadow plants and could not grow through deposited litter.Oosterveld [14] wrote about a high sensitivity of species belonging to the specialized sections such as: Erythrosperma, Celtica, and Palustria, suggesting that the main threat to these plants in the Netherlands was the fertilization of meadows, especially with phosphorus compounds.Even moderate fertilization of meadows accelerates tillering and growth of grasses, significantly increasing their competitiveness.
According to monographs of the section [2], only two species of marsh dandelion withstand such conditions, namely T. vindobonense and T. hollandicum.In Poland, the latter of these species is very rare [4], which does not allow us to identify its habitat preferences.However, the population studied by us, i.e., T. hollandicum, occurs on an unused, partly overgrown meadow, which confirms its high resistance to competition from high meadow plants.Taraxacum vindobonense, which is one of the most common species of the section Palustria occurring in Poland, has similar resistance.The optimum habitat for this species is unfertilized, extensively used meadows from the Molinietalia order; however, it is able to grow on quite intensively used and moderately fertilized meadows and pastures [2][3][4].The other species of the section are very sensitive and die due to the lack of meadow use, or as a result of intensified utilization.This sensitivity of marsh dandelion can be a good indicator of the intensity of use of naturally valuable wet meadows.This indicator can also be very helpful when assessing the effectiveness of activities concerning biodiversity protection, undertaken within agri-environmental programs or conservation measures plans for Natura 2000 sites.