Abstract
Invasions were studied at different spatial scales, however these scales were rarely compared. The aim of this study is to compare the rate of expansion of eight alien plant species within the borders of the city with expansion in the whole country and to analyse changes in distribution of these plant species in the last 30 years. We hypothesised that at the scale of the city, despite of stronger human impact, invasion processes will perform in a similar way as at the scale of whole country. Distribution changes of Bidens frondosa, Conyza canadensis, Echinocystis lobata, Helianthus tuberosus, Impatiens parviflora, Reynoutria japonica, Solidago canadensis and S. gigantea in 1 km squares grid was examined in the Warta River Valley in Poznań (W Poland) in 2013 and compared to data collected during 1980–1984. All species increased their distribution within the study area. E. lobata had the highest increment of occupied grid squares (from 0 in 1980’s to 28 in 2013), and S. gigantea had the lowest (from 8 to 9). Echinocystis lobata reached the highest invasion success, which results from species traits (hydrochory) and large propagule pressure from garden plots. Between species with different ecological traits residence time has relatively little influence on invasion success, however in cases of species with similar traits (S. canadensis and S. gigantea) residence time is a crucial factor determining invasion success. Although urban ecosystems are more vulnerable to biological invasions, this process occurs in a similar way as in the whole country. This similarity is connected with similar factors responsible for spread of invasive species: propagule pressure, time since introduction and spatial distributions of invasible habitats.
Highlights
River valleys are habitats which are vulnerable to biological invasions
The highest increment of occupied grid squares occurred for Echinocystis lobata, which was not recorded in the Warta River Valley in Poznań in the 1980s, but was found in 28 squares in 2013
Results of this study indicate that the range expansion of neophytes was observed in cases of species occurring mainly in frequently disturbed habitats (i.e. B. frondosa or C. canadensis), and species connected with late-successional stages, such as I. parviflora
Summary
River valleys are habitats which are vulnerable to biological invasions. River regulation and building embankments caused lack of episodic flows, which were responsible for shaping the successional gradient This gradient represents the range of successional stages from the most pioneer conditions near the river bank, where only some shrubs may exist, to river valley slopes, where persistence of the forest community has not been interrupted by floods and late-successional plant communities may occur (DeFerrari and Naiman 1994; Hood and Naiman 2000; Richardson et al 2007). River regulation increases the opportunities of invasion for many alien species of plants, especially those which benefit from ecosystem alteration (Cooper et al 2003; Jagodziński and Maciejewska-Rutkowska 2005a, 2005b, 2008; Catford et al 2011; Dyderski and Jagodziński 2014; Dyderski and Wrońska-Pilarek 2015)
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