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Both landscape gradient and temporal data confirmed that urbanization had the function of species conservations with sharp increases of alien species and tropical type plants.In the case woody species,60-yr urbanization in Harbin had induced increases of 9 families and 17 genera,and there were 7-20 more families,12-35 more genera,1.6-2.6 higher Margalef richness in urban areas than those in nature reserves and local forest farms; Increases in alien species(4-fold in 60-yr urbanization; 21%in urban area vs <2%for non-urban region)and tropical type plants(1.6-fold in 60-yr urbanization; temperate/tropical ratio at 1.2 in urban area vs >1.6 in non-urban area)were mainly responsible for these compositional changes,which can be proved by their significant correlations.