S07 - Session P2 - A research methodology to select tree species able to meet the challenge of climate change adaptation in cities: case study on street tree monitoring in Paris

Authors: Julien Thierry *, Sophie Herpin, Fabrice Rodriguez, Mathilde Renard, Marie Gantois, Pierre-Emmanuel Bournet

In the context of climate change, heatwaves frequency and intensity are increasing, especially in cities where the urban configuration enhance overheating and the quantity and the distribution of rainfalls is getting modified. Street trees can provide cities with climatic benefits thanks to evapotranspiration and cast shadows. However, the choice of the right species, able to resist to heat and drought conditions while keeping providing significant cooling benefits appears to be critical. In this prospect, the green spaces department of the city of Paris developed in 2018 a methodology ("Trees and Climate") aiming at understanding the behaviour of various species of trees during heatwaves and droughts. First, the whole population of street trees of the city of Paris was analysed. 9 species considered as the most vigorous and representative ones and having a rather good cooling potential as well as drought resistance capacity were selected. Then, 5 sites containing at least 3 individuals of one or more of the 9 selected tree species were chosen. Each tree (36 in total) was equipped with a set of meteorological sensors (air and globe temperature, air relative humidity and wind speed) mounted inside the crown. Nearby, lamp posts were equipped with the same sensors. The soil water availability was monitored with tensiometers installed in the pit. The tree physiological response was also assessed with a micro-dendrometer mounted on a branch together with the morphological characteristics of the trees which were measured using the LIDAR technology. Field surveys were conducted from May 2019 to April 2022. The methodology offers the possibility to compare different species located in one site and also one species in various sites. The cross analysis of the collected data is expected to help stakeholders select the most adapted species regarding both the resistance to drought and the microclimate mitigation.