The European Communication on Green Infrastructures encourages the use of wildflower verges, green walls, green roofs, etc. to mitigate the artificiality of the urban and rural environment. Green roofs are engineered ecosystems occupying underutilized urban spaces that rely on the plant cover to provide services, such as the reduction of temperature, retention of storm-water and enhancement of urban biodiversity. In this framework we explored the ability of some wild perennial species of arid and semi-arid grasslands to survive and colonize the substrate of the extensive green roofs of the Agricultural Sciences School of the University of Bologna. In mid-June 2015 young plants of Festuca ovina L., Thymus serpyllum L., Hieracium pilosella L., Acinos alpinus (L.) Moench, Sanguisorba minor Scop. and Achillea millefolium L., coming from wild local populations, were transplanted into containers (54×54×9 cm depth) forming the upper cover of a green roof. The plants were fertilized and then irrigated throughout the summer of 2015. The growth of the species (coverage and space occupation) was monitored approximately once a month, from August 2015 to May 2016. F. ovina reached the highest values of coverage, without any significant seasonal variations. T. serpyllum and H. pilosella reached moderate coverage values depending however on the seasons. A. millefolium showed very effective dispersal abilities, but poor coverage potential. It can be used as a filler species in multi-species green roofs. Our results showed that the wild local flora can be an important, though still poorly explored, reserve of biodiversity for a new generation of extensive green roofs, designed, following a careful selection of species, for the best possible performances of the services they provide.

Green roofs are frequently exposed to extremely hard condition, in particular in Mediterranean area due to the shallow depth and low water holding capacity of the substrate, and to the custom of reducing maintenance costs, avoiding irrigation. This study presents the effects of a hydrogel polymer on the hydrological behavior and on growth of Sedum hispanicum L. and Bromus erectus Huds. Plants were grown in six test beds containing 10 cm of substrate mixed with three concentration of hydrolgel: 0% w/w (2 modules with substrate itself), 0.3% w/w (2 modules) and 0.6% w/w (2 modules). Weather data were collected continuously, while runoff was measured for three events. The water losses, due to evapotranspiration (ET, in mm/day), were evaluated by measuring the difference between the daily changes in weight of the boxes. Furthermore, two plant traits (leaf dry matter content-LDMC and relative water content-RWC) were used to evaluate the ecological behavior of the species. RWC was measured during the runoff measurement; LDMC was measured at the beginning of the experiments and after 3 months. Preliminary results show that the presence of hydrogel strongly influence the retention performance of green roofs, in fact the higher the hydrogel concentration the higher the retention. Hydrogel increases the substrate water content at saturation, as well as the water available for vegetation and consequently the greater the hydrogel concentration and the greater the daily losses for ET. Regarding the ecological performance, the preliminary results show that the presence of hydrogel does not influence the species RWC, moreover the LDMC values show a decreasing after 3 months especially for Bromus. LDMC has been shown to correlate negatively with potential relative growth rate; the presence of hydrogel then helps the vegetation growth.

Although the ability of green roofs as stormwater source control technologies has been the topic of many recent studies, most conclude that a better understanding of full-scale hydrological performance and of the impact of different plant cover types is still needed. Based on these considerations, this research presents the results of 15 months of monitoring activity in Bologna (Italy) studying the hydrological performance of two adjacent full-scale extensive green roof plots with a different plant cover composition. One of the plots (SR) was planted with Sedum species (CAM) and the other (NR) with native herbaceous perennial species (C3). Continuous rainfall, runoff and weather data were collected and used to compare the effect of changing plant cover type on the green roof retention rate. Over the 15 months of this study, NR presented a 59% retention rate (111 valid events) whereas SR had a 52% retention rate (91 valid events). For 24 common events, with retention lower than 100%, the average difference between the NR and SR plot retention was 10%, confirming the higher water storage capacity, and therefore the higher retention rate, of the NR plot.

An analysis is made of the land use transformations over the last sixty years, as well as the consequences of these transformations on the naturalness of the territories of three municipalities of the “Nuovo Circondario Imolese” (Bologna, Italy). The selected municipalities are: Medicina, Borgo Tossignano and Castel del Rio, which represent the main territorial aspects of the “Nuovo Circondario Imolese”.The land use transformations are quantified through the GIS comparison of the land use maps of the years 1995, 1976, 1994 and 2003. The corresponding legends are transformed into the five categories of the first level CORINE Land Cover classes. The naturalness increases in the three territories throughout the period 1955-2003, but with different quantitative importance: limited for the territory of Medicina and progressively increasing from Borgo Tossignano to Castel del Rio. Urban areas increase too, but following a gradient opposite to the one concerning naturalness. The land use transformations in the “Nuovo circondario imolese” are similar to the trends reported for the same period in Italy as a whole and in many other European countries. Concerning the effects of land use transformations on the territory naturalness and biodiversity, our results highlight the critical state of the intensively used areas and the marginal areas. Some lines of action for a correct ecological planning of these different situations are suggested