Effects of dominant trees and anthropogenic disturbances on species richness and floristic composition of secondary communities in southern Poland

1. Woodland vegetation can be restored via natural succession in sites that are adjacent to woods which can act as seed sources for trees, shrubs and woodland herbs. The influence of the dominant tree species, Scots pine Pinus sylvestris is or black locust Robinia pseudacacia, and recreational disturbances on the Aoristic composition, species richness and spatial differentiation of communities that had developed in an abandoned sandy grassland over a 10-year period was studied in a suburban landscape in southern Poland. Data from 105 plots were used to determine the frequencies of various species groups and differences in soil conditions. 2. Canonical correspondence analysis (CCA) and step-wise regression analyses showed that pine and black locust had a strong impact on the species composition of young woodland communities, and that human activity, in particular trampling, affected the spatial differentiation of vegetation. The total number of species, and the number and cover of trees, shrubs and woodland herb species, increased along an ecocline that has developed as a result of regular disturbances, whereas the number and cover of grassland species decreased. 3. Cover of nitrophilous and ruderal species was most closely positively correlated with black locust cover; cover of heathland species with pine; and cover of woodland species with tree height. Grassland species were negatively correlated with tree height. 4, Soils under young secondary woods were richer in P, NO3-N and NH4-N than in adjacent sandy grassland. Symbiotic nitrogen-fixation and the fast growth of black locust contributed to the increase in soil NH4-N. Differences in nitrogen availability and light conditions appeared to cause the strong divergence in the development of different types of young secondary woods. 5. The species composition of secondary communities on poor sandy soils in a suburban landscape was thus indirectly determined by the dominant tree species, black locust or pine, and directly by recreational disturbances. Dispersal and colonization were important in determining which species of trees, shrubs and woodland herbs were present in a given site.