How does the 3-dimensional built environment and green infrastructure impact plant pollinator interactions?

Urbanization is a rapidly expanding global process that alters local environments and transforms landscapes. Despite extensive research on how urbanization in general influences biotic communities, little is known about how the 3-dimensional (3D) built environment (e.g., buildings of varying height, rooftops, etc.), inherent to cities influences species interactions and fitness. Using a unique plant model for tracking pollen movement (i.e., hermaphroditic and male-sterile rapid cycling Brassica), we investigated the effects of building height and roof type (green vs non-green) on pollen dispersal (Question 1) and plant reproductive success (Question 2). We found that buildings act as a barrier for pollen movement among plants from the ground to rooftops (Question 1), and building height negatively influenced pollination success of hermaphrodites (Question 2). Green roofs neither positively influenced the pollen transfer from the ground to roofs nor strongly influenced the plant reproductive success of hermaphrodites. However, hermaphroditic plants still experienced higher seed set on rooftops because roofs created unique environmental conditions that increased flower production. Our results suggest that buildings create a vertical barrier to pollinators, inhibiting the movement of pollen among plants growing at different heights. However, plants can maintain reproductive success when those negative effects of buildings on pollen movement are offset by environmental conditions that promote flowering on rooftops. Our study illustrates that understanding how the 3D built environment and greening initiatives affect urban species and their interactions can inform sustainable urban planning and development.