Weed synecology and dynamics in urban environment

Abstract

Forty vacant lots within the City of Montreal were studied during summer of 1983 for floristic composition. Despite a low floristic diversity per site — number of species per site varies around 23 — the whole sampling allowed us to record 136 taxa. Among these taxa, very few appear in more than 50% of the stands, suggesting a good discrimination between the 40 vacant lots. The data were analysed using principal coordinate analysis and hierarchic agglomeration cluster analysis. A study of the ordination and the dendrogram reveals eight phytosociological groups among which the most important are those dominated by Agropyron repens, Ambrosia artemisiifolia, Hordeum jubatum, Melilotus alba and Poa pratensis. Finally, dynamic relationships were identified between these groups which go from annual-dominated communities towards perennial-dominated communities.