THE VASCULAR PLANT SPECIES OF THE KRUG E BAGNO AQUATIC PEATLAND COMPLEX ( CZNA – W ODAWA LAKELAND )

This paper presents the richness of vascular plant species of the Krug e Bagno aquatic peatland complex and its structure. A field study was carried out in the growing seasons of 2008–2010. The aim of the study was to determine the species richness of the flora and its characteristics as well as to document changes in its composition taking place in successive years of the study. Based on the obtained results, it can be concluded that the stability of the qualitative and quantitative structure of the phytocoenoses and abiotic environmental factors bodes well for the maintenance of this aquatic peatland complex in good condition. However, due to the specificity of its species composition (a large proportion of stenobiontic species), it seems advisable to monitor regularly the biotic and abiotic conditions of this habitat.


INTRODUCTION
Plant species composition is expressed as the number of taxa occurring in a specific area.Monitoring and conservation of biodiversity, including plant species richness, have become priority actions both in the implementation of nature conservation strategies and in the restoration of natural systems [1].These actions cover different types of ecosystems, with special attention given to aquatic peatland habitats.Peatlands and peat pits are an important habitat for specific organisms which affect the stability of ecosystems and their biodiversity.Many peat pits, despite their anthropogenic origin, have great natural values and often deserve protection [2,3].
Stenotopic, and thus sometimes rare and protected, plant species are often associated with this type of ecosystems.Their specific abiotic requirements and low flexibility to changes in habitat conditions, on the one hand, allow them to occupy such extreme habitats, while on the other hand, small changes can cause disturbances in the functioning of their populations or even threaten their existence.The species of raised and transitional bogs are therefore a good indicator of any habitat disturbances [4].The changes in peatland plant species composition is reflected in a reduction in the number of locations of the most sensitive taxa [5].Research on the distribution of adventive species in wetland ecosystems in Poland has revealed that peatlands are relatively resistant to their expansion [6], although in large complexes of raised and transitional bogs significant enrichment of the flora with foreign elements is sometimes observed [7].
The aim of the study was to determine the richness of the vascular flora and its characteristics as well as to document changes in its composition taking place in successive years of the study.

MATERIALS AND METHODS
The research site of this study was the Krug e Bagno aquatic peatland complex located in the village of Jelino in the czna -W odawa Lakeland, south--eastern Poland.The present study covered the area of an open peat bog formed on the edges of overgrown pits left after peat extraction.It is a Site of Community Importance -SCI Jelino (PLH060095) -due to the occurrence of endangered fish species Eupallasella percnurus (Pall.).Krug e Bagno is located in the south-western part of the czna -W odawa Lakeland, in the buffer zone of the Polesie National Park (N 51 o 25' 29", E 23 o 02' 14'').This is a grouping of several small peat pits, characterized by an irregular bankline and surrounded by raised and transitional bogs which were created as a result of peat extraction at the beginning of the 20th century.Since then, they have been significantly overgrown with sphagnum mats.These are water bodies with an average depth of 0.6 m, a maximum depth of 1.5 m, and an area of up to 0.8 ha.The catchment of the study area includes forests and agricultural land [8,9].Fig. 1.Krug e Bagno aquatic peatland complex location and its surroundings [8] (1 -peatbog; 2 -post-excavation peat pools; 3 -forest; 4 -fields and meadows; 5 -buildings; 6 -roads) The vascular plant species of the Krug e Bagno aquatic peatland complex were the object of the study.A field study was carried out in the growing seasons of 2008-2010.
An inventory was made of all vascular plant species found in the entire area of the peat bog, taking into account species cover-abundance expressed as the degree of cover and using the Braun-Blanquet scale (with a modification).The degrees of cover for each species were used to calculate weighted mean values to determine habitat conditions existing in the study area.Botanical nomenclature followed M i r e k et al. [10].Syntaxonomic nomenclature followed M at u s z k i e w i c z [11].The following features were analysed: the biomorphological structure of the species composition according to R a u n k i a e r [12], the ta-xonomic and syntaxonomic structure at the class level following M a t u s z k i e w i c z [11], the historical--geographical structure and geographical elements of the flora following C h m i e l [13].
In analyzing the taxonomical data, the flora systematic diversity index was used, which was based on the following formula: Z S = the number of species + 5 x the number of genera + 25 x the number of families [14, cited after Olaczek, personal communication].
The degree of threat to the taxa was determined based on the Regulation of the Minister of the Environment of 5 January 2012 concerning plant species conservation [15] and on Z a r z y c k i et al. [12].
The plant species composition of Krug e Bagno was analyzed in terms of the number of locations of par-ticular species in Poland as well as their dynamic trends over the last decades according to Z a r z y c k i et al. [12].Based on the weighted mean values of some indicators of Z a r z y c k i et al. [12] (light and temperature, soil moisture content, trophic state and soil acidity), habitat conditions existing in the study area were determined.Three times a year, in situ measurements were made of groundwater pH (using a field pH-meter) and of electrolytic conductivity (using a field conductometer).

Species richness and taxonomic structure
Within the entire area of the K rug e Bagno aquatic peatland complex, the occurrence of 25 vascular plant species was recorded and they represented 19 genera belonging to 16 plant families (Table 1).The flora systematic diversity index was constant and it was 520 throughout the study period.
The Cyperaceae (4 species) and Ericaceae (3 species) plant families were represented by the most plant species.

Biomorphological structure of the species composition
In the plant species composition of the Krug e Bagno peatland complex, a predominance of two groups of plant biomorphological forms can be clearly seen, notably hemicryptophytes (31%, 10 taxa) and hydrophytes (24%, 8 taxa).Only one species was inclu-ded in the groups of therophytes (Bidens tripartita) and herbaceous chamaephytes (Comarum palustre; Fig. 2)

Syntaxonomic structure
The vegetation found in the Krug e Bagno bog showed a diverse syntaxonomic structure.The taxa currently present in the study area represented 8 clas-ses.Rush plants of the class Phragmitetea (5 taxa), peatland plants of the class Oxycocco-Sphagnetea (4 taxa), and species of the classes Molinio-Arrhenatheretea and Scheuchzerio-Caricetea nigrae (3 taxa each) had the highest percentage contribution (Fig. 3).

Historical-geographical structure
Only and exclusively native species were found to occur in the plant species composition of the investigated area and hence spontaneophytes ac-counted for 100% of the plant species.Among them, non-synanthropic spontaneophytes constituted 76% (19 species), while apophytes, being members of synanthropic native plant species, accounted for 24% (6 species).

Rare and protected species
The presence of 5 species legally protected under the Regulation of the Minister of Environment [15] was recorded among all vascular plant taxa found in the study area.These were Drosera rotundifolia, Ledum palustre and Utricularia minor, which are fully protected species, as well as Frangula alnus and Menyanthes trifoliate, which are partially protected.At the same time, Z a r z y c k i et al. [12] included Drosera rotundifolia and Utricularia minor in endangered species.
Taxa that have a large number of locations in Poland predominated in the species composition of the phytocoenosis of the studied peat bog (Fig. 4).A major part of these species have been observed to show a large decline in the number of locations or a decrease in population numbers in our country (Fig. 5).

Habitat conditions
A decisive majority of plant species found in the study area preferred moderate light conditions (84 %).
Few preferred semi-shade or light, but these were taxa of wider ecological tolerance.
The analysis of the temperature indicator values showed that a high percentage of species preferred moderately cool (44%) or moderately warm (43%) climatic conditions.
Based on the habitat preferences of the species determined on the basis of the indicator properties of plants according to Z a r z y c k i et al. [12], it can be said that the plant species of Krug e Bagna is predominantly composed of wet habitat species (57%) and moist habitat species (23%; Fig. 8) which prefer soils moderately poor (34%) or poor in biogenic elements (27%; Fig. 9) and which are primarily found in soils with acidic pH (pH 4 pH < 5; 25%) to moderately acidic pH (5 pH < 6; 28%) to neutral pH (6 pH < 7; 25%; Fig. 6).In the studied peat bog, the groundwater was acidic.In all years of the study, the mean water pH ranged from 5.21 to 5.31 in spring, 4.41 to 4.43 in summer, while in autumn these values were from 4.26 to 4.29.The mean electrolytic conductivity ranged from 50.6 to 61.3 in spring, 58.7 to 84.9 in summer, while in autumn from 42.3 to 48.7 S × cm -1 (Table 2).

DISCUSSION
The species richness of vascular plants in the Krug e Bagno peat bog is characteristic of oligotrophic aquatic wetland ecosystems of the temperate climate.At the studied site, 25 higher plant species were recorded.The species composition of the vascular plants of the peat bog remained unchanged throughout the study period.It was also similar to that observed in 1997 by B u c z y s k i and S t a n i e c [8].In a floristic inventory characterizing animal habitats of Krug e Bagno, B u c z y s k i and S t a n i e c [8] mentioned the occurrence of small clusters of Hydrocharis morsusranae L. in the water of the peat pits, but its presence was not recorded during the period 2008-2010.In 1997 and 1998 I w a n i u k [16] conducted an investigation of the Krug e Bagno plant species composition.At that time, he recorded three taxa (Carex canescens, Eleocharis palustris and Eriophorum angustifolium) whose presence was not confirmed during the present study (Table 1).In 2001 B u c z y s k i [17] recorded the presence of Carex lasiocarpa Ehrh., Utricularia vulgaris L., and Eleocharis palustris in the study area, but they were not found in 2008-2010.It can therefore be said that the species richness and taxonomic structure of Krug e Bagno are characterized by relatively low stability.
In spite of the close vicinity of human settlements, the naturalness of the plant species composition is confirmed by its geographical and historical analysis.Krug e Bagno, as a habitat of anthropogenic origin partially adjacent to land used by humans, has been colonized by native plant species characteristic of natural ecosystems.No encroachment of alien species is observed in this area.
Among 25 taxa whose presence was recorded in the Krug e Bagno peat bog, 5 are legally protected species.Not only the number of species, but primarily the significant numbers of their populations are evidence of their good condition at the studied site.Taking into account the relatively small number of taxa found in the study area, the proportion of environmentally valuable species in the plants of Krug e Bagno is substantial.
The species composition of the plants at the studied site was also used to determine the type of habitat.Krug e Bagno is a peat bog of problematic classification.Species characteristic of both raised and transitional bogs are found there.Among the species recorded in Krug e Bagno, Oxycoccus palustris and Ledum palustre are taxa characteristic of the continental stage of a raised bog [18], while Carex rostrata and Menyanthes trifoliata are considered to be peat-forming species for transitional bogs.On the other hand, Drosera rotundifolia is found in both types of bogs [19].
The peatland communities located in the Polesie National Park also show large variations.The close proximity of Krug e Bagno to these ecosystems allows one to refer to the studies conducted within the Polesie National Park.When observing the transitional bogs in the Polesie National Park, it can be noticed that their characteristic feature is the presence of sphagnum mats.The Krug e Bagno peatland complex is an area whose major part is covered by a moss and turf blanket mainly consisting of Spagnum sp.The acidic water pH, ranging 4-5 there, is not irrelevant, either [18].Water pH measurements in the Krug e Bagno peat bog made by B u c z y s k i [8] show that its water pH is at a level characteristic of transitional bogs, with its average value of about 4.7.It is accompanied by low mineralization, which is evidence of weak decomposition of organic compounds and water stagnation.These characteristics indicate that Krug e Bagno is a transitional bog which at the next stage of succession, after terrestrialization, will be transformed into a raised bog [18].
The analysis of published data and of the field observations in the study area do not allow the vegetation of Krug e Bagno to be classified unambiguously.The plant species composition and vegetation pattern confirm the findings of B u c z y s k i [8] who claimed that this bog has a mixed nature.An area of well-developed sphagnum mats overgrowing the peat pits can be classified as a transitional bog, while the higher situated areas with a large proportion of Ledum palustre and Eriophorum vaginatum as a raised bog [8].
The plant species recorded in the study area, represented by Oxycocco-Sphagnetea and Phragmitetea classes, are closely associated with high moisture content in the habitat and additionally with specific habitat requirements.The plant communities recorded in the study area (taxa of the classes Oxycocco-Sphagnetea and Phragmitetea) are closely associated with high moisture content in the habitat and additionally with specific habitat requirements.M a t u s z k i ew i c z [11] says that plant communities of the class Oxycocco-Sphagnetea occur in acidic oligotrophic or dystrophic habitats supplied only or mainly with rainwater.Associations of the class Phragmitetea are of enormous importance in the process of overgrowing water bodies [11].
The plant species composition of a habitat is strictly dependent on the abiotic environment.Thanks to the analysis of the species composition in terms of habitat preferences of particular species, habitat conditions of the studied site can be determined.The study conducted in the period 2008-2010 confirmed that the open space of the peat bog was characterized by high moisture content, this habitat was poor and extremely poor, and most species recorded there also indicated moderately acidic and acidic habitats.The waters of the peat bog were described as dystrophic by K o l e jk o and S e n d e r [20].The acidic nature of the habitat was confirmed by B u c z y s k i and S t a n i e c [8] as well as by K o l e j k o et al. [9], and their results were close to those obtained in 2008-2010.
The stability of the qualitative structure of the phytocoenoses as well as of the abiotic environmental factors bodes well for the maintenance of this aquatic peatland ecosystem in good condition.However, due to the specificity of its plant species composition (a large proportion of stenobiontic species), it seems advisable to monitor regularly the biotic and abiotic conditions of this habitat.
Handling Editor: El bieta Weryszko-Chmielewska This is an Open Access digital version of the article distributed under the terms of the Creative Commons Attribution 3.0 License (creativecommons.org/licenses/by/3.0/),which permits redistribution, commercial and non-commercial, provided that the article is properly cited.©The Author(s) 2014 Published by Polish Botanical Society

Fig. 4 .Fig. 5 .
Fig. 5. Contribution of plant species to the Krug e Bagno plant species composition with different dynamics of occupying new sites in Poland over the last decades Explanation: -2 -large decrease in the number of sites; -1 -decrease in the number of sites or reduction in the number of individuals; +/--disappearance of sites and appearance of new ones in balance; +1 -increase in the number of sites, marked increase in the number of individuals at sites; +2 -large increase and occupation of new sites

Table 1
Species richness of Krug e Bagno and its changes in 1997-2010

Table 2
Descriptive statistics of some groundwater parameters in the Krug e Bagno peat bog