Robert Hanczaruk and Agnieszka Kompała-Bąba
Department of Botany and Nature Protection, Faculty of Biology and Environmental Protection, University of Silesia in Katowice, Jagiellońska 28, 40-032 Katowice, Poland
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Urban river valleys belong to the ecosystems most vulnerable to plant invasions. A model example is the Kłodnica valley – the main river of Upper Silesian Industrial Region (Silesian Upland, Poland). It flows through large and densely populated towns as Katowice, Ruda Śląska, Zabrze and Gliwice. It has been subjected to strong anthropopressure caused both by mining and metallurgical industry, as well as, heavy urbanization since the end of the 18th century. As a result of human activity, existing plant cover was seriously transformed or even completely destroyed. In place of riparian forests (Fraxino-Alnetum) and willow-poplar thickets (Salicetum albo-fragilis), secondary communities developed. According to Corine Land Cover 2018, we distinguished 13 classes of land use. We examined (i) the differentiation of vegetation of the Kłodnica valley along a section that differs in reference to anthropogenous pressure (i.e. land use), and (ii) the distribution of invasive herbaceous plants along the Kłodnica valley in terms of land use.
We recorded 23 plant communities that were constituted by 173 vascular species. Among them, 17 invasive plant species were recorded. Some species occurred in the floristic composition of plant communities, whereas species such as Aster novi-belgii, Helianthus tuberosus, Impatiens parviflora, Reynoutria japonica and Solidago gigantea formed some aggregation. Solidago gigantea, Reynoutria japonica and Conyza canadensis occupied the highest number of localities. The results of the non-parametric Kruskal-Wallis test showed statistically significant impact of the land use on the distribution of invasive herbaceous plants (H = 11.83; p = 0.01). The mean number of invasive plants was higher in urban (8.17), sport and leisure (5.00), as well as industrial areas (4.80) than in agricultural and forest lands (2.67).
The distribution of invasive alien species along the Kłodnica river valley shows the strong connection with the pattern of land use. The river was exposed to strong propagule pressure from human-altered ecosystems. The areas most prone to invasion were urbanized areas with features such as: high population density, industrial sites and allotment gardens, where the level of anthropogenic disturbances and resources availability was high. In contrast, extensively used agricultural areas reduced the spread of exotic taxa. Arable lands played a role as a buffer, limiting the encroachment of invasive species to the forest, which occur in the surroundings. Our results showed that the land use metrics allows to determine the level of invasion and predict the future spread of exotic taxa. Therefore, landscape characteristics should be included in the management strategies of alien species.