Floristic diversity in selected city parks in southern Poland

Parks are an important element of green areas of cities and serve various purposes such as recreation, health and social functions and improving the condition of the urban environment [Breuste et al. 2013]. In general, their biocenotic function is ignored. Some parts of parks are fragments of transformed natural communities, such as forested or artificially planted areas, and nowadays are completely altered.

The developing processes of urbanization are usually accompanied by undesirable environmental and social problems, consisting mainly of drastic loss of natural habitat and its fragmentation, leading to deterioration of the environment in the form of reduction of green areas [Pukowiec-Kurda 2018] and straightening of rivers in cities and surrounding areas [Grimm et al. 2008]. Such action may lead not only to loss of biodiversity and disintegration of ecological systems [Haines-Young, Potschin 2010; Banaszek et al. 2014; 2017], but also to a reduction in the social value of urban areas. Urban green space refers to public spaces in city areas, mostly covered by different types of vegetation, which include urban parks, woodlands, street trees, square plantings and others social infrastructures. City parks are often designed along the river in many cities which also influences species composition and biodiversity. They are also elements of ecological network [Izakovičová, Świąder 2017].

The advantages of urban green areas are notable primarily in city parks, where valuable urban biotopes generate a varied set of substantial ecosystem services for people [Niemelä et al. 2010; Konijnendijk et al. 2013].

The concept of ecosystem services is defined as the benefits that people derive, directly or indirectly, from ecosystems and can be classified into provisional, regulating, cultural and supporting services in accordance with the Millennium Ecosystem Assessment [MEA 2005]. Biological diversity has been shown to play a key role at all levels of the ecosystem services hierarchy [Mace et al. 2012]. Efforts to mitigate global biodiversity loss have traditionally concerned large, biodiverse and relatively untouched natural habitats and ecosystems [Lovell, Johnston 2009; Cornelis, Hermy 2004; Rahmonov et al. 2013]. High biodiversity has also been observed in urban areas in urban parks or city parks. City parks are a specific ecological system in urban areas and are most often considered as green spaces for recreational purposes. They are defined as delineated open space areas, mostly dominated by vegetation and water, and are generally meant for public use. City parks are usually large, but many smaller ‘pocket parks’ also exist. City parks are usually locally defined (by authorities) as ‘parks’ [Konijnendijk et al. 2013].

Today, city parks are often created in areas changed by human activity and on artificially (anthropogenically) created grounds composed of rocks of diverse origin, from various geological periods, and characterized by diverse chemical compositions [Pukowiec-Kurda et al. 2019]. Such grounds and soils differ in their physical, chemical and water-retaining properties. Such conditions are the reasons that the formation of mosaic or micro-mosaic habitats and new ecological niches for various species with diverse ecological requirement can take place, from algae to flowers [Czaja et al. 2014; Rahmonov et al. 2016]. This is one of the most important causes of biodiversity in anthropogenic areas, including urban parks [Sikorski et al. 2012]. In contrast, parks created in natural ecosystems feature fewer plant species, due to their stability and a lesser degree of human interference. Urban parks, as one specific type of urban green space, constitute particularly important biodiversity hotspots in the cityscape [Nielsen et al. 2013].

The aim of this study is to present the ecological and floristic diversity of urban parks within the highly industrialized region of southern Poland, the former Upper Silesian Industrial District.

Studies on the composition of vascular plants were carried out in the years 2014–2019. The floristic material was collected in four cities in southern Poland (Fig. 1) in Silesian Voivodeship. Ten parks were chosen for investigation during this study: Grabek, Jordana (Czeladź), Hallera, Zielona, Sielecki (Dąbrowa Górnicza), Środula, Leśny (Sosnowiec), Góra Zamkowa, Syberka Niska and Park Wojkowice (Będzin). These parks have been formed at different times, on various parent rocks, both natural and anthropogenic transported ground [Rahmonov et al. 2018], have different size surfaces and fulfil the same function as outlined in Table 1.

Figure 1

The collected floristic materials (both native and alien plant species) were analysed in terms of life form, botanical family, geographical–historical groups and phytosociological affiliation of species. Classification of species with regard to their affiliation to geographical–historical groups [Kornaś 1968] and names of flowering plants and pteridophyte species were given by Mirek et al. [2002]. Urban parks flora was analysed in terms of the share of Raunkiaer’s life forms, ecological indicator values and phytosociological affiliation by following the works of Zarzycki et al. [2002], Rutkowski [2011] and Matuszkiewicz [2004].

The collected data were also subjected to statistical tests aimed to show whether there are statistically significant differences in the floristic composition in terms of geographical–historical groups of flora and life forms. First, the analysed parks were compared in terms of differences in the ratio of species representing a given geographical–historical group of flora using the chi-squared test (χ²), the significance level equal to α = 0.05. All sites were compared together, then with each other. Similarly, the parks were compared with each other in terms of the occurrence of individual life forms of plants. These tests were performed using the PAST 3.0 software [Hammer et al. 2001].

The progressing anthropogenic pressure in particular climatic zones has led to or will lead to the destruction of partial natural habitats or to their complete disintegration. This is manifested by the destruction or modification of habitats, the introduction of invasive species, overexploitation, environmental pollution, climate change and agricultural and farming practices which can lead to a reduced gene pool. This contributes to the reduction and loss of biodiversity at all levels: genetic, species and ecosystem. Sources of biodiversity in majority of city parks are often connected with their management and cares. High species diversity is often related to the park habitats as river valley, urban forests and housing estates [Breuste et. al. 2013; Cornelis, Hermy 2004].

Paradoxically, despite the occurrence of most of the abovementioned factors leading to the loss of biodiversity, the level of species diversity in urban parks is relatively high [Banaszek et. al. 2014; 2017]. Such diversity in these anthropogenic ecosystems is conditioned by many factors. This may result from the history of a given park, the reasons for its creation (e.g. parks near castles, palaces), its size, period of origin and ways of development, management or continuous modernization. Special microenvironments are created in the form of ponds or rockeries, also for plants from other climatic zones. These kinds of activities are decorative and increase the attractiveness of the park for the inhabitants of the surrounding regions even from an educational point of view. This is important, especially in areas of large polycentric agglomerations, which also include the analysed municipal parks. Modernization of the analysed parks today leads partly to the destruction and modification of habitats for the benefit of infrastructural elements.

An important ecosystem role, in terms of biodiversity, is played by the location of park establishment, the type of geological bedrock (limestone, sandstone and anthropogenic materials), the place of the park in the landscape (hill, riverside) and the features of the urban geosystem. Within the analysed parks, in several cases, the above-mentioned elements played a key role in the formation of the habitat and microhabitats. For example, the Góra Zamkowa Park was founded on a hill built of Triassic formations, and rocky outcrops are visible on the surface. The southern slopes are sunny and overgrown with xerothermic grasslands, and the semi-natural Tilio-Carpinetum forests develop on the northern slopes. The park is well decorated and subject to constant care. Such edaphic diversity contributes to the occurrence of taxa with different ecological requirements and in this way the flora is enriched.

In turn, parks that are located along rivers and water reservoirs have even contributed to the formation of azonal types of plant communities with incomplete species composition. These parks include Sielecki Park, Leśny (Sosnowiec) and Zielona in Dąbrowa Górnicza. Species enrichment in such conditions is often associated with transport of propagules by water from higher areas. A clear example is the migration of invasive species such as Reynoutria japonica occurring in all parks along the rivers flowing through them [Rahmonov et al. 2018]. Feeding birds with seeds is a potential source of emergence of new taxa, which were found several times by researchers [Tokarska-Guzik 2005].

Permanent human activity in the ecosystem of the city park leads to the formation of a variety of ecological niches on the background of mosaic habitat with a diversified surface. This does not allow the formation of typical plant communities. As a result, many species with diverse phytosociological affiliations can be found here. This situation was also found in similar objects [Dyderski et. al. 2017; Sender et al. 2016]. Many species are not bound to any plant associations.

There are species that can develop from extreme to optimal habitats. Extreme habitats in the areas of parks should be considered as soils with a high content of heavy metals [Rahmonov et al. 2019] and disturbed by trampling water–air relations in the soil cover in large surfaces. Trampling, in general, as a phenomenon has a positive effect on the formation of microhabitats and seed dispersion. Due to the above reasons, occurrence of species belonging to different phytosociological units in the park areas is justified. A significant number of species (189) is characteristic of more than one syntaxon. This clearly demonstrates the diversity of the habitat and ecological unpredictability (as during the primary succession), even when compared to the stabilizing ecological system.

In all parks, as in temperate climate, hemicryptophytes dominate in the structure of the life form. The structure of life forms of vascular flora may indicate the degree of naturalization of the vegetation of a given park. When a significant proportion of mega- and nanophanerophytes are found, it can be concluded that such a park has well-maintained greenery (a large proportion of typically park and ornamental species). The most number of megaphanerophytes, that is, 50 species, was found in the Grabek Park (Table 5). This is related to the fact that the ecosystem is heavily managed in terms of the decorativeness of the park, especially with the introduction of alien species. In turn, the least number of megaphanerophytes was found in the Zielona Park. This park was built within the natural oak-hornbeam forest, where alien species occur individually. The diversity of life forms is conditioned by the mosaic-like nature of the habitat (macro and micro landforms) and the presence of a potential biochore in the vicinity of urban parks.

In general, parks in the investigated region do not differ significantly in terms of geographical and historical groups. Differences in parks are visible only when comparing two specific locations, although in most cases the differences in the compared pairs are not statistically significant. According to Raunkiaer’s life forms, plants are much more diverse than in terms of geographical and historical groups.

The analysed parks are important links in floral diversity within highly urbanized areas in city centres. The variety includes both native species and typical park species of ornamental or alien origin which provide ecological services for science and society. Urban parks are excellent objects for investigations and aid in the preservation of biodiversity within cities. City parks, specifically older parks, are often a point of synanthropization of many plant species from surrounding areas.

Species diversity in anthropogenic ecosystems of urban parks is observed at all levels, especially at the species and ecosystem level. The reasons for high biodiversity in these ecosystems are conditioned by both natural and anthropogenic factors resulting from the introduction of species (native and alien) and the creation of new habitats and microhabitats.