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INVASIVE ALIEN WEED Conyza canadensis (L.) Cronquist IN URBAN AREAS OF THE ZAGREB COUNTY

Conyza canadensis (L.) Cronquist (Canadian fleabane) is a common and widespread alien invasive plant in Croatia, first recorded in 1847. However, systematic research on its occurrence and possible spread has not been conducted so far. Therefore, the aim of our work was to show the spatial distribution of Canadian fleabane in urban areas of the Zagreb County and to detect its possible spread. Therefore, in 2012 the species was mapped in all nine towns of the Zagreb County, on approximately equal plots (250x250 m2). Further, in 2016, the survey was repeated on the same plots in the towns of Dugo Selo (eastern part of the County) and Samobor (western part of the County), in order to determine the possible spread of the species. A total of 541 plots were surveyed in all towns in 2012, and C. canadensis was found on 362 plots (66.9%). In Ivanić Grad, the plant was found on 44 of the 73 surveyed plots, in Jastrebarsko on 32 of 48, in Sveti Ivan Zelina on 21 of 44, in Sveta Nedjelja on 19 of 31, in Velika Gorica on 33 of 76, in Vrbovec on 24 of 48, in Zaprešić on 39 of 58, in Dugo Selo on 21 of 54, and in Samobor on 71 of 109 investigated plots. A comparative analysis of the spatial distribution of Canadian fleabane between two "opposite" towns of the County showed a significant increase in the areas covered by C. canadensis in a four-year period: in 2016, it was recorded in Dugo Selo on all 54 plots, and in Samobor on 87 plots. It was additionally observed that the increase in the both areas is more significant in suburban and rural parts of the towns, and less in the urban parts, probably due to more regular maintenance.

Canadian fleabane, mapping of invasive alien plants, northwest Croatia, spatial distribution

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