: The creation of a network of trees as a green infrastructure as part of the Trees Master Plan. The plan has the overall objective of maintaining a well-managed, thriving and biodiverse woodland to enhance green corridors and deal with the urban heat island effect. (IUCN, 2019). As an illustration, some examples are provided below on theway the challenge of climate change is currently being addressed through the actions envisaged in the Barcelona Trees Master Plan:
• Species are selected for their suitability to the environmental conditions and resilience when faced with water and heat stress. Moreover, the city’s aim is not to allow trees of any one species to exceed 15% of the total of street trees in Barcelona. The logic behind this approach, which is being implemented gradually, is to avoid problems of vulnerability to pests and diseases inherent in mono-specific populations. The trees selected are preferably native species that are the most resistant to pests and diseases and best adapted to the low availability of water. When needed, pest control is mainly carried out using biological means.
• A limiting factor for street trees is that they usually have very little space in the ground for the roots, and are planted compact soil with little structure and scarce organic material for nutrition. In most instances, this is a result of the limited width of the pavements and area of the tree pits. Therefore, in the public area, streets wider than six meters are identified, as they provide the possibility of transforming individual tree pits into continuous pits. It is aimed to also improve tree pit conditions in the remaining areas with street trees.
• In response to water and heat stress there is an augmented use of runoff water in park and forest areas and the promotion of alternatives to drinking water for watering purposes. Moreover, plants with low water requirements are selected, and for each species of tree, the appropriate irrigation is established having regard to their biology and place and time of planting. Automatic irrigation systems for the watering of trees are in place, with regular controls for leaks. (Climate-ADAPT, 2019).
Increased infiltration, water retention and flood protection
Yes, trees are able to prevent potential local flooding by contributing to the reduction of storm water runoff. (Climate-ADAPT, 2019).
Improved air quality
Yes, the trees in Barcelona can remove more than 305 tons of air pollutants in a single year, providing an estimated value to society of 1.12 million Euros (numbers are for 2008). (Climate-ADAPT, 2019).
Reduced drought risk, cooling effect, urban heat island mitigation
Yes, through climate adaptation benefits. Trees alter the urban microclimate and mitigate the climatic conditions by creating a cooling effect through shade and transpiration. Additionally, the reflection of sunlight by the leaves lowers the temperature in pedestrian zones and the shade protects people from the sun’s rays, especially during the hot summer months. (Climate-AdDAPT, 2019).
Biodiversity conservation or increased biodiversity
Yes, trees conserve and boost urban biodiversity. Barcelona has more street trees than most other European cities. At present there are more than 200.000 trees of 150 different species lining the streets of Barcelona (roughly 1 tree for every 10 m of street), and new ones are being planted every year. If one takes includes the trees found in parks (about 36.000) and those in woodland areas (73.500), about 310.000 trees altogether are managed by the City Council.(Climate-ADAPT, 2019).
Yes, the Trees Master Plan has the overall goal of maintaining a well‐managed, healthy and biodiverse woodland to enhance green corridors (IUCN, 2019). The project improves the city’s ecological, environmental, social and economic services by linking various areas through vegetation to create an effective ecological infrastructure. (Climate-ADAPT, 2019).
Increased quality and quantity of green and blue infrastructures
Yes, by means of the implementation of a network of trees. According to the Plan vision, trees are deemed to be a fundamental part of the green infrastructure of Barcelona. The project provides a model of an urban green network and a city in which green elements are not just ornamental accessories but rather genuine green infrastructures. (Climate-ADAPT, 2019).
Yes, the project links various areas through vegetation to create an effective ecological infrastructure; the goal is to ensure a city model in which nature and urbanity are able to interact and enhance one another for the benefit of citizens, to allow them to improve their welfare through the natural heritage and be actively engaged in the safeguarding and betterment of all areas. Trees can improve the urban microclimate and mitigate climatic conditions by creating a cooling effect through shade and transpiration. In addition, the reflection of sunlight by the leaves lowers the temperature in pedestrian zones and the shade shelters people from the sun’s rays, especially during the hot summer months. Furthermore, trees prevent potential local flooding by contributing to the reduction of storm water runoff. Consequently, they can play a significant role in urban climate change adaptation. Trees can also supply several co-benefits. For instance, in a single year, the storage of carbon in the city’s trees adds up to 113.000 tons. (Climate-ADAPT, 2019).
Improved aesthetic value
Yes, trees also afford a more pleasant urban landscape. (Climate-ADAPT, 2019).
Increased access to green infrastructure
Increased social interaction and inclusion
Yes, trees and, more generally, plant cover, also can function as a place for socialisation or social gatherings, and as a location for taking a stroll or engaging in sports and leisure activities in the open air. The safeguarding of this green heritage is undertaken by the Barcelona City Council with the involvement of both public and private organisations and of the citizens themselves, through stakeholder participation and various volunteer activities. (Climate-ADAPT, 2019).
Increased willingness, participation, investment in NBS
Yes, by stakeholder participation. It is vital to engage citizens in the greening of the city. This need is addressed through actions on: - Participation: the City Council collaborates with sector-based and territorial associations and institutions generally, in relation to a specific space or group. For instance, when developing the Barcelona Citizen Commitment to Sustainability 2012-22 document, more than 800 entities were roped in, including businesses, civic and professional associations, trade unions, foundations, universities, schools and various areas and districts of the local administration. (Climate-ADAPT, 2019).
Provision of health benefits
Yes, trees and, more generally, plant cover, also mitigate noise and air pollution and regulate damp. According to the Plan vision, trees are considered a fundamental part of the green infrastructure of Barcelona, a natural resource that enables the enjoyment of a healthier life in the city. Trees and shrubs retain and boost urban biodiversity, link people with nature and supply social and environmental services (e.g. in relation to health, habitability, landscape, etc.) to the current population as well as future generations. (Climate-ADAPT, 2019).
Education, knowledge exchange and learning
Yes, it is absolutely crucial for citizens to become engaged in the greening of the city. This need is addressed through actions on communication and education: the City Council’s strategy is focussed on expanding citizen knowledge of the natural urban environment and its benefits, and promoting respect for green spaces. The actions included in this strategy include, for instance, the development and implementation of a communication strategy about trees, promoting education projects on trees in schools, encouraging citizen involvement in projects and the utilisation of new technologies for dissemination such as apps relating to trees. (Climate-ADAPT, 2019).
Low air quality
Yes, the effect of air pollutants emitted by urban activity, mainly vehicle traffic, must also be taken into account. (Climate-Adapt, 2019).
Drought and heat risk
Yes, Barcelona is particularly vulnerable to climate change. Its high population density also multiplies the local heat island effect, causing a range of health and environmental challenges. Main climate change challenges for Barcelona are related to temperature rise, a significant drop in precipitation and a rise in related extreme events such as droughts and heat waves. The high urban density can act as a driver worsening the heat island effect. Intense sunlight and high temperatures are aggravated by buildings reflecting sunlight instead of dissipating energy, due to the lack of evaporative surfaces, thus additionally heating up the atmosphere. (Climate-Adapt, 2019).
Low availability of green infrastructure
Yes, Barcelona has a relatively low ratio of green space to inhabitants (Climate-Adapt, 2019).
Low aesthetic value
Yes, the Plan has included the structuring of greenery actions at new pedestrian streets, squares and superblocks as a strategy to reclaim overtaken public spaces and add new functional and recreational pockets of productive greenery. (Jones, Wilenius, 2018).
Good health and well-being (SDG3)
Yes, the Master Plan also aims to improve the Barcelona population's health and comfort. (Climate-Adapt, 2019).
Sustainable cities and communities (SDG11)
Yes, the Master Plan aims to maximise environmental, social and economic services from Barcelona's trees. (Climate-Adapt, 2019).
Climate action, resilience, mitigation and adaptation (SDG13)
Yes, trees modify the urban microclimate and temper the Mediterranean city conditions by providing cooling through shade and transpiration. In addition, the reflection of sunlight by the leaves lowers the temperature in pedestrian areas, and the shade protects people from the sun, especially during the hottest months. (Climate-Adapt, 2019).
Terrestrial biodiversity (SDG15)
Yes, currently there are over 200.000 trees of 150 different species lining the streets of Barcelona (approximately 1 tree for every 10 m of street), with new trees being planted every year. When including the trees in parks (about 36.000) and those in forest areas (73.500) all together, about 310.000 trees are managed by the City Council. (Climate-Adapt, 2019).
IUCN. 2019. Nature based Solutions in Mediterranean cities. Rapid assessment report and compilation of urban interventions (2017‐2018). Malaga, Spain: IUCN. 117pp.
Naturvation project. 2019. Trees Master Plan. Information obtained: 2020-08-04. Available at: https://naturvation.eu/.