Drought tolerance and thermal effect measurements for plants suitable for extensive green roof planting in humid subtropical climates

This study aims to investigate the physiology, endurance, and environmental thermal regulatory effects of plants suitable for thin layer green roofs, to provide reference for plant selection in future green roofs. Water conservation and drought tolerance experiments are carried out on 31 types of plants in Taichung, in central Taiwan. The drought tolerance of various plants was investigated. Thermal effect experiments were performed on 10 types of plants. The results from this study show that plants suitable for thin layer green roofs resist drought conditions through physiological mechanisms such as succulent foliage, surface cuticles, mucilaginous substances, hairs or spines, and the Crassulacean acid metabolism (CAM). Plants that grew well came from the families Crassulaceae, Euphorbiaceae, and Portulacaceae. When temperature reduction effectiveness was measured in regard to plant height, the best reductions in temperature occurred in 35 cm plants, followed by 15 cm and then 10 cm plants. Green leafed plants have better temperature reduction effects than purple/red leafed plants. The plants suggested in this study are suitable for regions with subtropical climates. Selecting thin layer green roof plants that resist drought, survive well, and decrease temperature effectively can adequately use water resources and realize green building concepts such as ecological friendliness, energy conservation, carbon emissions reduction, and water conservation.