: Milan’s Vertical Forest is made up of two towers of 80 and 112 meters respectively, accommodating 480 large and medium trees, 300 small trees, 11,000 perennial and covering plants and 5,000 shrubs over an urban surface of 1,500 m2, serving as the equivalent of 20,000 m2 of forest and undergrowth. The selection of species and their distribution according to the orientation and height of façades is the fruit of three years of studies carried out together with a group of botanists and ethologists. The plants which are uutilised on the building were pre-cultivated in a nursery so as to accustom them to conditions akin to those prevailing on the balconies. Subsequent to micro-meteorological studies, a calculation of irrigation requirements was accomplished by examining climatic characteristics and was diversified to cover all the planting areas by taking into account the exposure of each façade and the distribution of vegetation on each floor. (Boeri Studio, 2020). The living wall system was completely integrated into the facade construction, with plants and planting media being both located on the vertical surface of the exterior walls. Thanks to this setup, the irrigation systems can be complemented by rain sensors to render the living wall's needed irrigation more efficient and sustainable (Giacomello, Valagussa, 2015).
: 181.8 km²
: 3,140,181 (World Population Review, 2020)
: 8 years
: Co-governance or hybrid governance (mix of responsibilities between government and non-government actors)
Reduced drought risk, cooling effect, urban heat island mitigation
Yes, the Vertical Forest helps to build a microclimate and to filter fine particles contained in the urban environment. The diversity of plants helps to develop the microclimate which produces humidity, absorbs CO2 and particles, produces oxygen, and protects against solar radiation. (Boeri Studio, 2020).
Biodiversity conservation or increased biodiversity
Yes, the Vertical Forest boosts urban biodiversity. It encourages the formation of an urban ecosystem where various plant types (100 different plant species: 15 species of trees, 45 shrubs, and 34 types of perennials) create a separate vertical environment (Giacomello, Valagussa, 2015; Naturvation project, 2020), but which works within the existing network, able to be inhabited by birds and insects (with an initial estimate of 1,600 specimens of birds and butterflies). A number of species of bugs such as ladybugs have been introduced to combat pests, obviating the need for pesticides. Thus, the Vertical Forest constitutes a spontaneous factor for repopulating the city’s flora and fauna. (Boeri Studio, 2020).
Increased quality and quantity of green and blue infrastructures
The Vertical Forest is an architectural concept which replaces traditional materials on urban surfaces, using the changing polychromy of leaves for its walls. The biological architect relies on a screen of vegetation, needing to create a suitable microclimate and filter sunlight, and rejecting the narrow technological and mechanical approach to environmental sustainability. (Boeri Studio, 2020). The first analysis of the NBS impacts after the first year of the implementation stated that it is evident that the presence of terraces and additional trees decreases the amount of collected solar radiation during the winter season by 32% and 21% for configurations “C.a” (external walls, green terraces, trees) and “C.b” (external walls, green terraces, NO trees) respectively, compared with configuration “C.c” (external walls, NO green terraces, NO trees), thus resulting in 44% and 24% higher space-heating energy needs, respectively. On the other hand, in configurations “C.a” and “C.b”, terraces and trees block 49% and 35% of the solar radiation entering the reference floor in summer, compared with configuration “C.c”, thus making it possible to decrease space-cooling energy consumption by about 68% and 46% respectively. (Giacomello, Valagussa, 2015). The facade temperature registered during the summer is 30 degrees lower thanks to the water vapour emitted from the watered plants (Giacomello, Valagussa, 2015; Naturvation project, 2020). The diversity of plants protects against noise pollution (Boeri Studio, 2020). An indicator that turned out negatively for this NBS was the time dedicated to tree maintenance, as Giacomello and Valagussa (2015) observed that the time for pruning one tree in the vertical forest is five times higher than pruning a tree with the same characteristics at ground level. This implies high maintenance costs (Giacomello, Valagussa, 2015; Naturvation project, 2020).
Improved aesthetic value
Yes, the first example of a ‘Vertical Forest’ (il Bosco Verticale) formed part of a broader renovation project of two towers of 80m and 112m. It is a constantly evolving landmark of the city, whose colours change according to the season and the different nature of the plants used. This regales the local residents and passers-by an ever-changing view of the city (Boeri Studio, 2020). (Boeri Studio, 2020).
Increased access to green infrastructure
Yes, the city of Milan was planning to renew this derelict area since the 50s, but could not do it due to financing shortages. Green buldings were designed with the goal of introducing reforestation in that area of the city using efficiently the limited space available (Giacomello, Valagussa, 2015; Naturvation project, 2020).
Drought and heat risk
The Mediterranean Region is considered as a "hot-spot" of climate change, having been identified in global climate scenarios as one of the most responsive regions to climate change (Lionello and Scarascia, 2018). There is a consensus in scientific literature that average temperatures will rise across most of the Mediterranean Region, and that precipitation will decrease (Ulbrich et al. 2013; Lionello and Scarascia, 2018). Observed annual mean temperatures in the Mediterranean Region are now 1.4 °C higher than the average late-nineteenth-century levels particularly during the summer months (Cramer et al., 2018).
The Vertical Forest is an anti-sprawl system which aids in controlling and restricting urban expansion. In terms of urban density, each tower amounts to the equivalent of a peripheral area of single-family houses and buildings of around 50,000 m2 (Boeri Studio, 2020).
Low aesthetic value
Good health and well-being (SDG3)
Sustainable cities and communities (SDG11)
Climate action, resilience, mitigation and adaptation (SDG13)
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Lionello, P., Scarascia, L. 2018. The relation between climate change in the Mediterranean region and global warming. In Regional Environmental Change, 2018, Volume 18, Issue 5, pp 1481–1493.
Murtas, R., Russo, A.G. 2019. Effects of pollution, low temperature and influenza syndrome on the excess mortality risk in winter 2016–2017. BMC Public Health 19, 1445. https://doi.org/10.1186/s12889-019-7788-8.
Ulbrich U, Xoplaki E, Dobricic S, García-Herrera R, Lionello P, Adani M, Baldi M, Barriopedro D, Coccimiglio P, Dalu G, Efthymiadis D, Gaetani M, Galati MB, Gimeno L, Goodess CM, Jones PD, Kuglitsch FG, Leckebusch GC, Luterbacher J, Marcos-Moreno M, Mariotti A, Nieto R, Nissen KM, Pettenuzzo D, Pinardi N, Pino C, Shaw AGP, Sousa P, Toreti A, Trigo RM, Tsimplis M. 2013. Past and current climate changes in the Mediterranean region. In: Navarra A, Tubiana L (eds) Regional Assessment of Climate Change in the Mediterranean. Springer, Dordrecht, pp 9–52. https://doi.org/10.1007/978-94-007-5781-3_2.