Comparison of neophyte communities of Robinia pseudoacacia L. and Acer negundo L. in the eastern Baltic Sea region cities of Riga and Kaunas

Abstract

In this study, we examined the species composition of neophyte communities of Robinia pseudoacacia andAcer negundo and compared the site conditions of the urban environment of two cities—Riga and Kaunas.Eighty-five plots of A. negundo and R. pseudoacacia communities were selected. Within each plot, all of thevascular plant species were recorded, and their abundance was estimated in 2014. Composite soil samplesof the 0–10 cm mineral topsoil were collected for the estimation of the soil chemical properties at ninesystematically distributed points in each sample plot. The soil pHKCL, exchangeable bases, total nitrogen,total organic matter, C/N ratio, and concentrations of the elements (P, K, Ca, Mg, Fe, Mn, Zn, Cu, Na, Pb, Cd,and Ni) were estimated. Canonical correspondence analysis was used to analyse the vegetation data. Anindicator species analysis was carried out. The relationship between the soil chemical parameters wasassessed by principal component analysis, and the results showed that structure and composition of theplant communities of A. negundo and R. pseudoacacia differed. The number of species was lower and theherb layer was more developed in R. pseudoacacia communities, whereas the structure of communitiesdiffered between Riga and Kaunas. The cover of the shrub layer was more developed in Riga. The numberof species in A. negundo communities was similar, whereas the number of species in R. pseudoacaciacommunities was lower in Kaunas. Alien species were more frequent in Riga. Neophyte communitiesin Kaunas were more homogenous. The soil in communities in Riga had more carbon, was richer innutrients and more acidic than in Kaunas. R. pseudoacacia grew in more fertile soils than A. negundocommunities. The differences between the neophyte communities in Riga and Kaunas were caused bydiffering geological parameters, soil development and urbanization effects.