The management of street trees was already included as an action in the earlier Barcelona Green Infrastructure and Biodiversity Plan 2020 (BGIBP), which is the “umbrella” strategic plan for actions related to green infrastructure and biodiversity in Barcelona. Besides setting out an action plan, the BGIBP provides for a model of an urban green network and a city where green elements are not ornamental accessories but rather genuine green infrastructures. In the broader context, the BGIBP is a component of the overall efforts the city of Barcelona is making in terms of sustainable development and resilience to climate change. In particular, with the BGIBP Barcelona seeks to enhance the city ecological, environmental, social and economic services by connecting various areas with vegetation to produce effective ecological infrastructure. The aim is to secure a city model where nature and urbanity interact and enhance one another for the benefit of citizens, to enable them to derive welfare from the natural heritage and be actively engaged in the protection and improvement of all areas.
Because of the relevance of trees a Trees Master Plan is being completed as a separate document remaining in line with the goals of the BGIBP. To have trees being appreciated as a true urban infrastructure of first order and to favour cooperation between the municipal departments 10 strategic lines constitute the basis for the Trees Master Plan. These include: heritage and biodiversity, planning and connectivity, plant material, land, water, safety and pruning, health of trees, preservation and protection, knowledge, and communication and participation. These 10 lines will be displayed by 46 actions and a range of associated tasks that have been prioritised considering mandates and the timing of actions for the coming years.
As an illustration, some examples are below given on how the challenge of climate change is currently addressed through Barcelona Trees Master Plan’s actions:
- Species are selected suited to the environmental conditions and resilient to water and heat stress. Furthermore, the city’s aim is for no one species to exceed 15% of the total of street trees in Barcelona. The reasoning behind this approach, which is being achieved gradually, is to avoid mono-specific populations vulnerable to pests and diseases. The species chosen are more resistant to pests and diseases, the best adapted to the low availability of water and preferably native. When needed, pest control is mainly approached through biological control.
- A limiting factor for street trees is that they mostly have very little space in the ground for the roots, with very little organic material and compact soil with little structure and deficient nutrition. In most instances, this is caused by the small width of the pavements and the tree pits. Therefore, in the public area, streets wider than six meters shall be located as they provide scope for transforming individual tree pits into continuous pits. Tree pit conditions shall also be improved in the remaining areas with street trees.
- In response to water and heat stress there is an increased use of runoff water in park and forest areas and alternatives to drinking water for tree watering are promoted. Furthermore, plants with low water requirements are selected and for each species of tree the appropriate irrigation is determined according to their biology and where and when they are planted. Automatic irrigation systems are in place for the watering of trees and there is controlling for leaks for these systems.
While Barcelona has a relatively low ratio of green space per inhabitant, it has more street trees than most other European cities. 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.