Abstract
Most of the services and benefits of green roofs are related to the substrate as well as the vegetation layer. Although plant selection should be made on the basis of green roof typology, morphology, and climate conditions, very often, Sedum species only are used worldwide. However, they do not always guarantee the best performances; hence, it is important to investigate different plant species and their performance in different climate contexts. Herein, an experiment was conducted using three plant mixes (i.e., a Sedum mix, a perennial herbaceous mix, and a suffruticose mix), grown in boxes containing two substrates (a volcanic substrate or a recycled crushed brick substrate) and two drainage/storage layers (a preformed layer or a mineral layer), in factorial combination. The Sedum mix showed a high canopy cover, comparable to or even higher than that of the other mixes, particularly when supplemental irrigation was stopped. However, the actual crop coefficient (Kcact) of the herbaceous and suffruticose mixes was often higher than that of the Sedum mix. The results also showed that both the substrate and the drainage/storage layer may improve Kcact values as a consequence of their capacity for stormwater retention.
Highlights
The presence and coverage of plants have great influence on the services and benefits of green roofs [1], among which the most appreciated are those related to stormwater management, such as the delay in runoff peak and the direct retention of a portion of the rainfall, even if most of this retention is a function of the growth substrate [2,3,4,5]
SF coverage strongly decreased as a consequence of drought, which resulted in the death of several plants
Our results proved once again that Sedum species can survive without supplemental irrigation during summer, while irrigation is mandatory for other species
Summary
The presence and coverage of plants have great influence on the services and benefits of green roofs [1], among which the most appreciated are those related to stormwater management, such as the delay in runoff peak and the direct retention of a portion of the rainfall, even if most of this retention is a function of the growth substrate [2,3,4,5]. The vegetation and substrate of green roofs can provide a wildlife habitat for many species and can improve biodiversity [1]. Urban surfaces and roof coatings contribute to the urban heat island (UHI) effect. Green roofs can mitigate the UHI effect and can improve building energy performance thanks to the characteristics of their layers and the presence of vegetation. Green roof vegetation can mitigate air temperature via evapotranspiration phenomena, but albedo (reflectivity) is a key determinant of roof temperature, with more reflective vegetation correlated with lower surface temperatures [6,7,8,9,10]
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