The role of soil and microclimatic variables in the distribution patterns of urban wasteland flora in Brussels, Belgium

Despite increased recognition of the importance of urban vegetation research, few attempts have been made to assess the relative influence of ecological variables on the species composition of urban wastelands. The main aim of this paper is to assess the relative importance of soil and microclimatic variables in structuring plant species richness and diversity in this habitat. Field investigations were carried out in 22 wasteland sites situated within the city of Brussels. The vegetation has been recorded in 38 4 m2-plots according to the Braun–Blanquet-method. A total of 19 environmental variables were taken into consideration, among others the presence of different kinds of anthropogenic substrates and microclimatic variables. Results indicate that plant species composition in urban wastelands is mainly driven by soil nutrient content, soil moisture, soil pH and light intensity (as inferred by the mean Ellenberg's indicator values). Various types of anthropogenic substrates such as concrete, pebbles, sand and rubble had different effects on the species composition, the proportion of neophytes, hemeroby and urbanity level. Air temperature and humidity did show a significant influence on the presence of some species. The contribution of these environmental variables to the species composition and diversity of urban wastelands is discussed.