Urban forest fragmentation can highly influence pollinator-plant interactions in close contrasting habitats of a local herb, Ajuga decumbens (Labiatae)

Frequent anthropogenic activities in urban regions may result in fragmentation, sequentially forming a variety of forest edges. The contrasting habitats (forest interior vs. edge) may differ in foster pollinator and plant diversity, but little is known about the influence of urban forest fragmentation on pollinator-plant interactions. Six patches of a local bee-pollinated herb, Ajuga decumbens (Labiatae) were used to detect the edge effect. The patches from both the forest edge (three patches) and interior (the other three patches) habitats were close to reduce the differences in pollinator fauna, in an urban fragmented forest in Wuhan city, China. We investigated the pollinator species richness and abundance as well as the reproductive success of the plant across the forest edge and interior habitats. Results revealed that the pollinator assemblage and fruit set of the plant differed between the forest edge and interior habitats, plants from the forest edge had higher pollinator abundance and yielded more fruits than those from the forest interior. Although the patches were close enough for the pollinating bees to fly over, forest edges resulting from fragmentation intensely changed the pollinator assemblage of the local herb. Where the fragmentation of urban forest is unavoidable, our results indicated that the forest edge should be a friendly urban matrix for the local herb and its bee pollinators. Thus, anthropogenic actions e.g. road hardening and introduction of ornamental flowers should be avoided in areas where the forest edges have already been generated by urban construction.