Abstract
Two species of the genus <em>Petasites</em>, <em>P. kablikianus</em> (occurs upstream) and <em>P. hybridus</em> (occurs downstream), form characteristic tall herb communities in two altitudinal zones of Carpathian streams and rivers. They are described as “altitudinal vicariants” due to their substitution with decreasing elevation on similar habitats along mountain streams. This would indicate that the phenomenon is conditioned by climatic factors. In this study, we investigated the factors that determine this substitution on streambanks, and whether <em>P. hybridus</em> competes with <em>P. kablikianus</em> and limits its spread from mountains to foothills. We analyzed 72 plant patches from the Western and Eastern Carpathians in terms of flora composition, and geomorphological features of the habitat. The content of organic matter, available Mg, P, K, C, total N, and pH were also analyzed for a representative group of patches. Phytocoenoses were analyzed based on the presence of one of the analyzed species or on the quantitative proportions, in the case of a co-occurrence. We found statistically significant differences in the soil structure (skeleton percentage), content of Mg, N, and C, and the values of the C:N ratio. These results revealed that <em>P. kablikianus</em> prefers skeletal soils with a lower clay content, that is rich in Mg, N, C, and organic matter. <em>Petasites hybridus</em> prefers finer soils, which are richer in pulverized and clay fractions, in a zone of decrease of soil richness and where a thick layer of humus is typical for its phytocoenoses. We found that the spread of <em>P. kablikianus</em> into lower locations is not limited by competition with <em>P. hybridus</em>, but rather by the quality and structure of the habitat. Therefore, both species should be treated as ecological rather than altitudinal vicariants.
Highlights
Riparian vegetation is an example of a transitional environment between stream water and surrounding areas
Essential feedback occurs between the vegetation and fluvial processes, which have a fundamental effect on the character and dynamics of the riparian habitat mosaic [3] and plant composition
Analysis of phytosociological data revealed that phytocoenoses with butterburs became gradually impoverished from 208 species in the Pk group, 164 in the Pk/Ph group, 171 in the Ph/Pk group, to 141 species in the Ph group
Summary
Riparian vegetation is an example of a transitional environment between stream water and surrounding areas. The vegetation forms characteristic zones according to the frequency of flooding [1]. Closest to the water current are the most frequently flooded communities of pioneer vegetation, followed by tall herbs or rushes, willow thickets, and riparian forests. The lower the location above sea level, the better formed the vegetation zones. In these zones, geomorphological, hydrological, and ecological processes interact actively, generating a highly dynamic landscape that is characterized by a heterogeneous mosaic of microhabitats [2]. Essential feedback occurs between the vegetation and fluvial processes, which have a fundamental effect on the character and dynamics of the riparian habitat mosaic [3] and plant composition.
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