Linking urban landscapes to ecosystem services and carbon flows: A European analysis.

In the context of population growth and urbanisation, associated with an increase in the concentration of GHG (greenhouse gases) in the atmosphere, the impact of human activities on climate change is ever increasing. Simultaneously, the pressure on natural ecosystems, especially in and around cities, is intensifying. Natural ecosystems associated with the urban forest (all elements of urban vegetation) can play an important role in mitigating climate change, especially in cities. In addition, they can contribute positively to the quality of life and wellbeing of urban dwellers. The dynamic of the services they provide, to Earth and mankind, vary between and within cities and need to be better understood.

This thesis focusses on the impact of the spatial integration of the urban forest on the supply and demand of ecosystem services. The main objective is to provide insights into how urban forms and their inner characteristics are related to ecosystem services (ES) and to carbon dioxide (CO2) profiles. In particular, it analyses the level of integration of the urban forest present within the built up footprint and anthropogenic land, in order to derive the effect of their spatial distribution on 5 ES provided by the urban forest.

The research is conducted at detailed spatial resolution for hundreds of Functional Urban Areas (FUAs) in Europe. It is structured as follows. We built an Urban Forest typology for Europe: 689 urban areas in 10 clusters and gathered in 4 groups (Forest cities, Herbaceous cities, Anthropogenic cities and Standard European cities). The typology reveals how nature is spatially integrated into urban structures. The metrics used in the typology reflect the potential supply and demand of 5 urban ES associated with the urban forest: micro climate regulation, macro climate regulation, air quality regulation, rainwater runoff regulation and physical and mental health. All cities are ranked according to an overall score. One of our main conclusions is that, given the same forest cover, a spatially integrated urban forest makes cities less sensitive to urban stressors.

We then focus on a specific regulatory ES: macro climate regulation. The Urban Carbon Balance (UCB) model has been developed and allows the estimation of the urban carbon balance at a high spatial and temporal resolution for a large number of areas, using land used and emission data. The UCB model has been applied to 802 European urban areas. We downscaled anthropogenic CO2 emissions to a spatial resolution of 1 ha before applying a temporal decomposition of annual, monthly and finally daily emissions, following year-, sector- and country-specific guidelines. For a typical day of each month, we simulate 3 steady-state situations for the dispersion and sequestration of CO2 molecules. We find that the urban structure and the level of integration of the urban forest contribute positively to helping urban areas sequester their own emissions.