Low plant diversity and floristic homogenization in fast-urbanizing towns in Shandong Peninsular, China: Effects of urban greening at regional scale for ecological engineering

• An investigation of man-made urban flora in 15 fast-urbanizing towns for effects of urban greening on the local and regional plant diversity.
• Huge investment to urban greening contributes to high urban green coverage but do not foster high plant diversity.
• Exotic species has lower overall dissimilarity between town pairs than native in either cultivated or wild flora.
• Both wild and cultivated flora show homogenizing tendency, yet the main driving forces are different.

Urban forest construction is believed as an effective method to preserve urban biodiversity and restore urban green ecosystem. However, in some fast-urbanizing towns, the most urban flora in the built-up area was almost totally manmade, where is new expanded areas mainly transformed from cultivated lands. How such urban flora contribute to local and regional diversity is seldom quantitatively tested. In this study, we conducted a comprehensive investigation of man-made urban flora in 15 fast-urbanizing towns in Shandong Peninsular, China, to explore the effect of urban greening on the local and regional plant diversity. The results that showed huge investment to urban greening contribute to high urban green coverage but do not foster high plant diversity. Exotic species has lower overall dissimilarity between town pairs than native in either cultivated or wild flora. Urban greening does not result in high proportion of exotic species, however, either wild flora or cultivated flora show homogenizing tendency due to the expansion of exotic species. Nevertheless, the main driving forces are different: the wild flora are homogenized by diminished species richness difference while the cultivated flora due to the decreased species replacement. We therefore suggest biodiversity conservation should be more considered and strengthened in further urban greening. Our study could also provide useful reference data in biotic homogenization research in China.