Rocks and walls: Biodiversity and temperature regulation of natural cliffs and vertical greenery systems

• A novel framework comparing vertical greenery systems and natural cliffs is proposed. • VGSs can act as temperature buffer towards the building wall at day and night. • VGSs host more animals than non-vegetated walls, but less than natural cliffs. • Biodiversity on VGSs increases with vegetation thickness and its plant diversity. Loss of natural habitats and increased human activity results in warming up of cities and a reduced biodiversity. Vertical greenery systems (VGSs) have been proposed to mitigate rising temperatures and the loss of biodiversity. So far, studies on existing VGSs have only analysed a single ecosystem service and their performance has not been compared to that of their natural counterparts. Here, air and surface temperature measurements as well as biodiversity observations were conducted on two different types of existing VGSs (climber, foliage) on buildings in Singapore and compared to non-vegetated building walls and vegetated natural cliffs. Our results show that VGSs act as temperature buffer creating a cooling layer towards the building wall during the day and a warming layer during the night. Furthermore, VGSs host significantly more animals than non-vegetated walls, however, VGS have less animals than vegetated natural cliffs. Moreover, a positive correlation was found between the amount of surrounding vegetation (green cover, tree density within 10 m of VGS), thickness of vegetation, plant richness on VGS and biodiversity observed on VGSs. Together, VGSs not only contribute with their aesthetics but can also be used to regulate daytime temperature in a tropical city like Singapore and to mitigate, at least in part, the loss of habitat for biodiversity.