Tree biodiversity in USU green space: exotic plant and its risk to native species.
Globally, urban ecosystems provide important green spaces for biodiversity conservation. Many exotic species are grown in tropical urban ecosystems, and their harmful effects on native species and pollinator communities have been widely documented. Therefore, the purpose of this research is to determine the origin (native or exotic to Indonesia, sexual and reproductive system) of tree species on the University of Sumatera's (USU) campus. Field inventory methods were used in this study for observed tree species on the USU campus. All tree species were observed, their flowering observed if any. According to our research, the USU green area comprises a collection of 121 tree species. Seventy species (57.85%) are native to Indonesia, while 51 species (42.15%) are exotics from other tropical regions. In terms of individual abundance, these values are 37.28% native and 62.72% exotic. The exotic trees on the USU campus show monoecious and dioecious flower sexuality; 19 species are hermaphrodite, two species have self-incompatibility characters, seven species are dioecious, and 23 species are monoecious. Together with the results from the few other experimental studies, it concluded that the increase of exotic species plantation in USU campus might indicate risk for animal interactions (e.g., pollination; dispersal), threaten reproduction of native plant species, pollination specialization, habitat, and other life-history properties. Therefore, the use of these exotic species needs special attention for stakeholders at USU.