臺灣原生地被植物於薄層綠屋頂生長適性與降溫效益評估──以臺灣中部地區為例

Evaluation of Growth and Thermal Benefits of Taiwan Indigenous Ground Cover Plants for Extensive Green Roofs–A Case Study in Central Taiwan

世界各大都市之熱島效應日益加劇，設置綠屋頂已被公認為最好的都市降溫方法之一。臺灣位於亞熱帶地區，可使用於緩解都市夏季屋頂高溫之地被植物尚無廣泛試驗研究。本研究以試驗法選拔適合臺灣中部都市建築薄層屋頂綠化使用，且能快速達到高綠覆效果之臺灣原生地被植物。在9種試驗植物中，具最佳匍匐性，能快速擴張且生長勢強的地被植物種為全年生長佳的鴨舌癀與糯米糰，以及夏季成長佳的仙草與蠅翼草。研究過程中亦發現此4種地被植物的匍匐莖於夏季能迅速擴張覆蓋土表，且能溢盆外拓長出直接覆蓋在高溫達60℃的樓版上，仍生長良好；於中午最高溫時段，直接覆蓋在樓版的匍匐莖葉可為樓版降溫達9-25℃，植槽內下方樓版則可降溫達21-26℃。在夜間，綠化對樓版具有保溫的效果。於清晨最低溫時段，於植栽槽內下方樓版溫度比裸露樓版高約3-5℃，匍匐莖葉直接覆蓋之樓版溫度約與裸露樓版相等，故綠化可明顯減少夏天樓版熱漲冷縮的幅度而達保護建物及降溫之效果。建議未來可利用此類地被進行薄層綠屋頂綠化，可以最小的種植面積達到2-5倍的綠覆效果，除可減少綠屋頂建造費用，又可有效降溫，達節能減碳與減緩都市熱島效應之效果。

The urban heat island effect is becoming more severe in many cities in the world as a consequence of more intensive urbanization. Installation of green roofs is regarded as one of the best ways to reduce high temperature in urban areas. Taiwan is located in subtropical region, however, the usage and efficiency of indigenous ground cover plants to mitigate high summer temperature for extensive green roofs have not been extensively explored yet. The research employed empirical approach to screen indigenous plant species that can achieve rapid green coverage for green roofs in Taiwan. Based on previous studies, 9 indigenous species were selected in this research, in which Phyla nodiflora and Gonostegia hirta grow vigorously all year round, while Mesona procumbens and Desmodium triflorum could also grow very well during summer. The 4 species could grow out of the planting box and sprawling on floor when its temperature was higher than 60℃at noon in summer. When the plants sprawling directly over the slabs, the temperature of the slabsat noon could be reduced by up to 9-25℃during summer, furthermore, the slab temperature underneath the planting box was reduced by 21-26℃. During the night the planting box showed heat insulating effects for slabs. On the other hand, while the air temperature dropped to daily minimum at dawn,the heat beneath the slab of the planting box was retained making the temperature of the slab 3-5℃warmer than bare floor. The slab temperature beneath the sprawling plants was nearly equal to the bare floor. Therefore, it could be concluded that these sprawling plants can protect the building from intensive thermal expansion and contraction of roof top slabs in summer and reduce floor temperature. The indigenous ground cover plants are recommended for setting extensive green roofs in urban area of central Taiwan. Owing to the ratio of green cover is 2-5 times higher than planting area, the installation expenses is lower than conventional roof gardens. More ground cover plants on building roof could reduce floor temperature substantially to save air conditioning energy and mitigate urban heat island effects.