Contribution of green roofs and walls to ecosystem services of urban green

This paper reports a literature review of the large-scale ecosystem services (ESS) which green roofs and walls can provide for cities. A short overview of 17 ESS’s is given. Much research has been done on ESS’s meeting immediate physical human needs and providing long-term physical and socioeconomic security. Services meeting social and psychological needs have been less studied. In general, ground-level urban vegetation like parks can provide a higher level of ESS’s than green roofs and walls, but the latter are a valuable addition where ground-level room is scarce. Of roof and wall types, intensive green roofs provide the highest level of ESS’s. Extensive green roofs mainly satisfy physical needs, and green walls mainly satisfy social and psychological needs. Green roofs and walls can probably contribute the most to the reduction of the Urban Heat Island effect, and to the processing of annual rainfall. It is not possible yet to translate all ESS’s into a financial value, for easy comparison of their impact. Recent research points to health benefits and savings on energy and emissions as candidates for the largest effects of green roofs and walls in financial terms