Actual and potential flora in the streets of Padova: considerations for a sound weed management

Floral surveys on six sites in the town of Padua (4 in residential and 2 in industrial areas) were carried out along the pavements at four different times of year. The surveys included both actual and potential flora. Weed species were divided on the basis of biological and eco-physiological groups, type of dissemination and botanical family. The vegetation was analysed using cluster analysis and principal components analysis. The environmental dynamics of a hypothetical herbicide was simulated with the model SOILFUG using the physical and chemical characteristics of the substrate. A total of 145 species were found in the actual flora and 83 in the potential flora. The average potential flora varied between 340 and 29060 seeds per 100 linear metres (mean = 6188, median = 3200) of kerbside. Cluster analysis of the actual flora showed a separation between the two sites in the industrial zone and those in the residential areas. A large percentage of species is present throughout the year and no clear correspondence exists between potential and actual flora. There is a wide variability in space and time that renders the urban flora largely unstructured. Pre-emergence herbicides have to be used with care to control weeds along urban streets: they should be applied at reduced rates and only in the most infested areas.