There has been increasing recognition of the important role trees play in cities’ quality of life. Taking as the beneficial effects of trees as an empirical starting point, many cities, including Lisbon, have always incorporated trees in street planning. The increasing degree of rigour when assessing and quantifying the environmental (or ecosystem) services provided by a city’s trees has led to great international interest in the subject. Of particular note in Europe is the European Cooperation in the field of scientific and technical research, the COST action "Urban forests and trees" and the essential book resulting from it, edited by Cecil Konijnendijk and others in 2005. In the United States, as a result of the STRATUM model developed by Greg McPherson, another modelling tool appears in 2006, the i-Tree, developed in partnership with Forest Services (USDA-FS). David Nowak played an important role in the designing of this tool and its application in a number of cities.

The trees found in Lisbon streets have been the subject of important studies, such as that of Teresa Andresen in 1982, but only  in 2006, a first quantification of street tree ecosystem services was by Ana Luísa Soares and Francisco Castro Rego, through the STRATUM model. Similar work was undertaken in Porto, using the more recent i-Tree model, by Marisa Graça in 2017.

In terms of inventory, it should be noted that since 2006 Lisbon Municipal Council (CML) has invested in the cataloguing of the greenery in Lisbon, in particular its georeferencing as a management and maintenance tool. By the end of 2018 some 48 000 street trees had been georeferenced.

The aim of this agreement is to undertake studies to quantify the ecosystem services provided by urban trees, by taking inventory and analysing it, making comparisons with previous inventories taken in the city, as well as employing the tools that allow that quantification to be performed. The work will be divided among the following tasks:

It is estimated that during task 1, the number of trees to be catalogued is around 14000, and it is important to distinguish between the need to make a survey and the need to georeferenced the greenery in some boroughs where less information is available (the boroughs of Alvalade, Beato, Lumiar, Marvila, Penha de França and Santa Clara); during task 2 the data that boroughs already have will be updated, and this calls for verifying around 30 000 trees (the boroughs of Ajuda, Alcântara, Areeiro, Arroios, Avenidas Novas, Belém, Benfica, Campo de Ourique, Campolide, Carnide, Estrela, Olivais, Parque das Nações, Santa Maria Maior, Santo António, São Domingos de Benfica and São Vicente); task 3 calls for the inserting of the data collected in the previous tasks to the GIS (geographical information systems) so that they may be used in later phases of the project and other applications of interest to CML. Task 4 focuses on the quantifying of the ecosystem services provided by street trees which will be based on the previous inventory phases. Task 5 includes the disseminating of the results and communicating with the public, which will be on-going throughout the other tasks. By the end of the project a session open to the general public will be held, the date of which will be set in line with CML commitments as the Green Capital of Europe 2020. Also forecast is a CML publication setting out the results of the project, containing the data collected, images and articles.

The research undertaken under this agreement will assess the benefits of urban trees, so as to show which species should be valued and used in the city. Account will be taken of their ecology and aesthetic values, their resistance to pests and disease, their state of conservation, and their geographic origin and/or their invasive behaviour. The aim is to contribute to enhancing the value of street trees, and at the same time support the decision-making model, within urban planning, through tree management founded on landscape architecture and urban ecology.