The European Communication on Green Infrastructures (1) encourages the use of reedbed, wildflower verge, green walls, green roofs, etc. to mitigate the consequences of the artificiality of the urban and rural environment. As far as the green roofs are concerned, they are engineered ecosystems occupying underutilized urban spaces, that rely on the plant cover to provide services, such as reduction of roof temperature, retention of stormwater, enhancement of urban biodiversity (2). Researches aiming at quantifying the green roof performances, depending on the physio-ecological characteristics of the plants used in their realization, are not yet fully developed (3). The Sedum species have been widely employed because of the extreme abiotic conditions they can tolerate. Recently, however, the importance to distinguish between the ability of a species to survive on a green roof and his ability to provide valuable services, starts to be considered. In the harsh conditions of green roofs, Sedum species may have the highest survival, even without some irrigation. However, other species are more likely to provide multiple, effective green roof services compared to a Sedum monoculture, if a moderate irrigation is foreseen. Irrigation during very dry periods would allow to employ a more diversified plant community and the improvements in green roof performances, could offer a high return on the investment of time and money (4). In this framework we explored the ability of some wild herbaceous perennial species of the arid and semi-arid grassland communities (Xerobromion and Mesobromion communities), to survive and colonize the substrate of a commercial extensive green roof system, adopted by the University of Bologna in the realization of the green roofs of the Agricultural Sciences School. The native plant species represent a rich heritage, to now not fully explored, which can be profitably used for the production of plant cover in green roofs of high environmental quality, well adapted to the conditions of the site where they are realized. The plant material was collected in natural and semi-natural plant communities of the Emilian Apennines, then cultivated and reproduced at the Azienda Agraria of the Bologna University (AUB) and finally utilized for the realization of the plant cover of an experimental green roof. For each species, the same number of young plants was planted in plots of 50x60 cm, at the mid June 2015, irrigated during the overall 2015 summer season. The irrigation was then suspended at mid September 2015. We report here the main results of a monthly monitoring (from June 2015 to April 2016) of the growth and colonization capacity of four of the species under study. For each species, different parameters were monitored, depending on its particular way of growth, in order to better describe the ability to cover the plot surface. Festuca ovina L, a perennial caespitose, showed a great capacity of shooting. During the 2015 summer, under irrigation, the number of shoots increased very quickly. Shooting capacity slowed in autumn, but at mid-end winter 2016 restarted. Water availability greatly influenced the shoot production. Hieracium pilosella L. is a stoloniferous creeping species. Stolons are important structures for the vegetative propagation as well as for the space colonization; they elongate mainly in the autumn and winter months. New leaves arranged in a basal rosette and floral axes are produced at the rooting points of the stolons. Sanguisorba minor Scop. is a medium size plant with a cluster of basal leaves that progressively enlarges all around. We measured the increase of the projection of the canopy on the horizontal surface. Maximum increase occurred at the start of autumn 2015 and in spring 2016, whereas in the winter months its cover progressively decreases. Achillea millefolium L. has solid, mat-forming rhizome/root system and fine feathery leaves which make it drought resistant. Both sexual and vegetative reproduction coexist and both are very efficient. The number of individuals produced through vegetative propagation regularly increases all over the observed period. After a period of acclimatation, all the species under study survived in the green roof artificial environment, even without particular cares. Each of them has a particular strategy and period of maximum development. Undoubtedly they represent an interesting pool of species whose eco-physiological characteristics could be explored, in order to better define their utilization for different performances and environmental services of urban green roofs.
NATIVE PERENNIAL HERBACEOUS SPECIES FOR NEW COVERS OF GREEN ROOFS
SPERANZA, MARIA;FERRONI, LUCIA;D'ARCO, MATTEO;VELLI, ANDREA
2016
Abstract
The European Communication on Green Infrastructures (1) encourages the use of reedbed, wildflower verge, green walls, green roofs, etc. to mitigate the consequences of the artificiality of the urban and rural environment. As far as the green roofs are concerned, they are engineered ecosystems occupying underutilized urban spaces, that rely on the plant cover to provide services, such as reduction of roof temperature, retention of stormwater, enhancement of urban biodiversity (2). Researches aiming at quantifying the green roof performances, depending on the physio-ecological characteristics of the plants used in their realization, are not yet fully developed (3). The Sedum species have been widely employed because of the extreme abiotic conditions they can tolerate. Recently, however, the importance to distinguish between the ability of a species to survive on a green roof and his ability to provide valuable services, starts to be considered. In the harsh conditions of green roofs, Sedum species may have the highest survival, even without some irrigation. However, other species are more likely to provide multiple, effective green roof services compared to a Sedum monoculture, if a moderate irrigation is foreseen. Irrigation during very dry periods would allow to employ a more diversified plant community and the improvements in green roof performances, could offer a high return on the investment of time and money (4). In this framework we explored the ability of some wild herbaceous perennial species of the arid and semi-arid grassland communities (Xerobromion and Mesobromion communities), to survive and colonize the substrate of a commercial extensive green roof system, adopted by the University of Bologna in the realization of the green roofs of the Agricultural Sciences School. The native plant species represent a rich heritage, to now not fully explored, which can be profitably used for the production of plant cover in green roofs of high environmental quality, well adapted to the conditions of the site where they are realized. The plant material was collected in natural and semi-natural plant communities of the Emilian Apennines, then cultivated and reproduced at the Azienda Agraria of the Bologna University (AUB) and finally utilized for the realization of the plant cover of an experimental green roof. For each species, the same number of young plants was planted in plots of 50x60 cm, at the mid June 2015, irrigated during the overall 2015 summer season. The irrigation was then suspended at mid September 2015. We report here the main results of a monthly monitoring (from June 2015 to April 2016) of the growth and colonization capacity of four of the species under study. For each species, different parameters were monitored, depending on its particular way of growth, in order to better describe the ability to cover the plot surface. Festuca ovina L, a perennial caespitose, showed a great capacity of shooting. During the 2015 summer, under irrigation, the number of shoots increased very quickly. Shooting capacity slowed in autumn, but at mid-end winter 2016 restarted. Water availability greatly influenced the shoot production. Hieracium pilosella L. is a stoloniferous creeping species. Stolons are important structures for the vegetative propagation as well as for the space colonization; they elongate mainly in the autumn and winter months. New leaves arranged in a basal rosette and floral axes are produced at the rooting points of the stolons. Sanguisorba minor Scop. is a medium size plant with a cluster of basal leaves that progressively enlarges all around. We measured the increase of the projection of the canopy on the horizontal surface. Maximum increase occurred at the start of autumn 2015 and in spring 2016, whereas in the winter months its cover progressively decreases. Achillea millefolium L. has solid, mat-forming rhizome/root system and fine feathery leaves which make it drought resistant. Both sexual and vegetative reproduction coexist and both are very efficient. The number of individuals produced through vegetative propagation regularly increases all over the observed period. After a period of acclimatation, all the species under study survived in the green roof artificial environment, even without particular cares. Each of them has a particular strategy and period of maximum development. Undoubtedly they represent an interesting pool of species whose eco-physiological characteristics could be explored, in order to better define their utilization for different performances and environmental services of urban green roofs.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
