Shrub encroachment in non-wooded habitats in Riga. II. Distribution patterns, ecology and plant communities of Robinia pseudoacacia and R. luxurians.
This paper presents the results of a study on shrub encroachment in non-wooded habitats in Riga, Latvia. In particular the paper discusses the distribution patterns, ecology and plant communities of Robinia pseudoacacia and R. luxurians. The community was classified as association Chelidonio-Robinietum and divided into two variants-typicum and var. Festuca rubra. The species characteristic for var. typicum are Aegopodium podagraria (V constancy class), Taraxacum officinale, Stellaria media, Glechoma hederacea, Chelidonium majus and Impatiens parviflora (III-IV constancy class). The species typical for var. Festuca rubra are Dactylis glomerata and Elytrigia repens [Elymus repens] (IV constancy class) and Festuca rubra (III constancy class). In var. Festuca rubra, there is larger proportion of plant species typical for moist soils and species with sub-oceanic distribution, while in var. typicum the largest proportion of species are nitrophilous, characteristic for moderately moist soils and with oceanic to sub-oceanic distribution. Finally, the paper establishes that the composition of neophytic woody plant communities reflects the contemporary transformation processes in urban environment: ruderalization-increasing proportion of annual and perennial plant species typical for heavily modified habitats (ruderals), graminification-expansion of graminoids in xerohpytic and eutrophic or contaminated environments, formation of early stages of shrublands and forests, and nemoralization-increasing proportion of nemoral (deciduous broadleaved) woody and herbaceous species in eutrophic environment, especially in urban areas.