Assessing the contribution of urban forest to ecological connectivity and net ecosystem services supply in densifying cities

Oral Presentation Abstract: Urban nature-based solutions (NBS), especially urban forests, have become popular among policy makers and built environment professionals for their potential to provide multiple co-benefits and mitigate multiple societal challenges. However, urban NBS assessments usually do not consider: i) environmental impacts of NBS (both, positive and negative) over their entire life cycle; and ii) the influence of the local urban context (e.g. building density) on ES demand and supply. We present a modelling framework that assesses the positive (ES) and negative environmental impacts of urban forests over their entire life cycle. It acknowledges that changes in ES supply and demand over time are dynamic and it works at two levels: foreground (dynamic) and background (steady state). This generates a semi-dynamic modelling framework where local impacts during the operational phase of the NBS intervention are considered dynamically. In contrast, the implementation and end-of-life phases as well as remote impacts are assumed steady state. Moreover, the modelling framework includes an ecological connectivity module, and takes into account the influence of the local context on the ES supply and demand. The modelling framework is tested by evaluating four planning options for the regeneration of a former industrial district in Esch-sur-Alzette (Luxembourg). The options have been developed during a competition held by a public-private consortium. They differ in the amount, density, and spatial arrangement of trees and buildings. The application of our modelling framework allowed to measure the impacts on ES supply and demand due to the compositional and configurational variations of the natural and built features associated to each planning option. In addition, it provided insights on the effects on ecological connectivity at urban and peri-urban levels. The potential and limitations related to the use of our approach to support real-life urban plans is presented and discussed. Keywords: nature-based solutions, system dynamics, biophysical assessment, densification, functional connectivity