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Abstract
Despite the fact that green roofs are based upon living systems, the majority of published research literature contains little specific information on the contribution of plants to the various functions and properties of green roofs. Further-more, there has been little investi-gation of the influence of the composition of vegetation on the physical properties of a green roof system. This paper reviews previously published material that throws light on the role of vegetation composition on green roof function, with particular regard to hydrology and biodiversity support. Two current experiments at the University of Sheffield, UK, are considered: a) Comparison of quality and quantity of run off from different vegetations. A lysimeter experiment that investigated the quantity of runoff from trays containing 100mm (3”) of growing medium and combinations of grasses and herbs, together with bare substrate. The composition of the vegetation was found to significantly affect both the amount of water retained and released from the system. In summer, trays containing substrate only were found to retain more water than trays with vegetation. b) Comparison of flowering season and biodiversity support of different vegetations. Comparison of the length of flowering period of mixed grass and herb vegetation compared with sedum vegetation in 100mm growing substrate indicates significant differences in invertebrate food sources over the course of a growing season. The range of options that have been explored for non-intensive green roofs is generally very limited. Ask someone to describe a green roof and the chances are that they will visualize a rather uniform sedum or grass covering. This reflects the types of green roofs that are available commercially, but it does result in a uniformity of vegetation type that goes against notions of regional distinctiveness and character. A very limited range of tried-and-tested plants is routinely used. This is, of course, partly a result of necessity: on shallow extensive roofs which are subject to the most extreme environmental conditions only a restricted range of specialized species will survive. However, it is also apparent that there is relatively little investigation into widening the types of plants and vegetation that may be used in a green roof context.
Despite the fact that green roofs are based upon living systems, the majority of published research literature contains little specific information on the contribution of plants to the various functions and properties of green roofs. Further-more, there has been little investi-gation of the influence of the composition of vegetation on the physical properties of a green roof system. This paper reviews previously published material that throws light on the role of vegetation composition on green roof function, with particular regard to hydrology and biodiversity support. Two current experiments at the University of Sheffield, UK, are considered: a) Comparison of quality and quantity of run off from different vegetations. A lysimeter experiment that investigated the quantity of runoff from trays containing 100mm (3”) of growing medium and combinations of grasses and herbs, together with bare substrate. The composition of the vegetation was found to significantly affect both the amount of water retained and released from the system. In summer, trays containing substrate only were found to retain more water than trays with vegetation. b) Comparison of flowering season and biodiversity support of different vegetations. Comparison of the length of flowering period of mixed grass and herb vegetation compared with sedum vegetation in 100mm growing substrate indicates significant differences in invertebrate food sources over the course of a growing season. The range of options that have been explored for non-intensive green roofs is generally very limited. Ask someone to describe a green roof and the chances are that they will visualize a rather uniform sedum or grass covering. This reflects the types of green roofs that are available commercially, but it does result in a uniformity of vegetation type that goes against notions of regional distinctiveness and character. A very limited range of tried-and-tested plants is routinely used. This is, of course, partly a result of necessity: on shallow extensive roofs which are subject to the most extreme environmental conditions only a restricted range of specialized species will survive. However, it is also apparent that there is relatively little investigation into widening the types of plants and vegetation that may be used in a green roof context.
Date
5/2005
5/2005
Author(s)
Nigel Dunnett; Ayako Nagase, Rosemary Booth; Philip Grime
Nigel Dunnett; Ayako Nagase, Rosemary Booth; Philip Grime
Page(s)
Keyword(s)
green roof; vegetation composition
green roof; vegetation composition