New trees to improve well-being on campus

With its iconic buildings that have sprung up on the Ecublens campus over the years, the EPFL has progressively distanced itself from nature, a feeling that is reinforced by the ongoing and future construction of new buildings, such as the RTS complex to the east and the Advanced Sciences Building (ASB) planned for the west. This densification is today accompanied by a reflection and concrete actions to bring back vegetation on the open spaces. This movement is part of the ambitions of EPFL's Climate and Sustainability Strategy, one of whose objectives is to approach a 30% canopy index by 2030.

Between February and March 2023, no less than 200 trees of thirty different species, 450 shrubs and 30 fruit trees were planted on campus under the direction of the Outdoor Spaces group of the Sustainability Unit at the Vice Presidency for Responsible Transformation (VPT). These plantings are in addition to the 82 potted trees already installed on campus during 2022 as part of the Campus Piéton project, which will be planted at a later date once work is completed on the affected area. In 2019, for the 50th anniversary of EPFL, a first series of 50 trees had already appeared.

Planting in the right place

"The idea is to plant in the right place, taking into account climatic and ecological, landscape, heritage and social issues," explains François Dupuy, landscape architect in charge of the team. According to him, a resilient campus can only be conceived "with the benefit of a generous tree planting to be passed on to future users".

By 2070, we can expect Lausanne's climate to resemble that of the Balkans today. The choice of species was therefore made to allow the trees to thrive in the decades to come, with a mixture of native species, from the Mediterranean basin and southeastern Europe, all raised locally. It will take twenty years for these trees to reach full maturity, and continued planting over the next fifteen years to significantly improve the campus climate, already marked today by too much concrete and impervious space.

"Trees are a climate damper that mitigates heat islands and the risk of flooding, continues François Dupuy. The canopy absorbs CO₂ while diffusing water vapor. This process cools the ambient air. In the shade of a tree, the temperature is lowered by at least 5°C. Strategic placement of trees can therefore reduce the air temperature of an urbanized area by 2°C to 8°C."

Ecological corridor

Beyond the climate, the presence of trees on campus offers multiple benefits, adds the manager: they are beneficial to health, improve the living environment and contribute to social ties; they mark the landscape and, moreover, promote biodiversity by serving as an ecological corridor for birds and small mammals.

The choice of locations was made taking into account all these parameters, as well as the constraints of the campus operation, such as traffic for deliveries, maintenance of facades, or festive events requiring large spaces, such as the Balelec festival, to name but one.

The main locations chosen for this first stage of planting are the south and west of the Rolex Learning Center, near the cantonal road and Place Cosandey, Maryam Mirzakhani Road, west of EPFL Pavilions, as well as several areas in the north of the campus, along Route de la Sorge and Avenue Forel, notably around the Rivier and Forel parking lots.

The 591,621 m2 of campus land currently includes about 1300 trees, as well as about 39,000 m2 of forest. This represents less than 18% of canopy cover. To reach 30%, it is estimated that there should be at least 2500 mature trees on campus with a crown diameter of 10 meters.

"Our implementation strategy combines a proactive attitude with an opportunistic approach. Trees must be the driving force behind new projects, and must be included in all work sites that offer planting opportunities," concludes François Dupuy.