Abstract
The aim of the present study was to describe the distribution of xerothermic species of vascular plants in the lower San River valley and the relationship between their density and the intensity of selected environmental (natural and anthropogenic) factors. Xerothermic species occurred more frequently in the present valley floor compared to the glacial terrace. Within the present valley, the highest density was observed in the floodplain. The examined species also occurred more often on steep slopes of the valley, at the margins of the present valley terraces, and in the area of occurrence of aeolian sands. Moreover, a positive correlation has been found between the number of xerothermic species and the area of polyhemeroby ecosystems. The distribution of xero- and thermophilous species is determined by natural edaphic and geomorphological factors as well as anthropogenic ones (land use, lowering of the groundwater level as a result of river regulation).
Highlights
The group of dry and warm habitat plants, depending on the adopted criteria, may be recognized in various manners
The species which seem to prefer this part of the valley include Astragalus cicer, A. glycyphyllos, Bromus erectus, Koeleria macrantha, Lathyrus sylvestris or Scabiosa ochroleuca
The species more commonly found in the bottom of the whole present valley are, e.g., Agrimonia eupatoria, Filipendula vulgaris, Carex praecox, and Fragaria viridis
Summary
The group of dry and warm habitat plants, depending on the adopted criteria (syntaxonomy, ecological indicator values), may be recognized in various manners. They are the taxa associated with dry grasslands of the class Festuco-Brometea This group often includes plants typical of other syntaxa like Trifolio-Geranietea, Koelerion glaucae, Onopordion, Agropyretea, Berberidion, Prunion fruticosae, and Quercetalia pubescenti-petraeae as well as a number of other species with a wider ecological amplitude, but most often occurring in thermophilous communities in the given region. In the landscape of river valleys, it is the steep and insolated slopes, usually rich in calcium and devoid of dense forest vegetation, which are the optimum for thermophilous plants In such places typical dry grasslands, forest edges communities, thermophilous scrub and sparse forests are formed. Apart from the optimal habitats, a certain number of xerothermic species is always present throughout the river valley They most commonly occur in the drier parts of river terraces, erosion edges, pioneer and ruderal habitats. They grow on dry meadows and sandy grasslands, on balks, fallow lands, roadsides, scarps and in areas heavily transformed by man (Kucharczyk , 2001; Skrzyczyńska and Rzymowska , 2001; Skrzyczyńska and Stachowicz , 2007; Myśliwy , 2010)
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