Renewing our green spaces

CERN’s poplars were planted 50 years ago to soak up the surplus water in the ground beneath the Laboratory’s sites. Now that they have reached the end of their life-cycle, some of the poplars are in danger of falling or losing their dead branches. On Saturday, 17 April, as part of the campaign launched in February at Prévessin, work will start on replacing the poplars on central areas of the Meyrin site.


Replanting plan for the Cedars and kindergarten carparks.

In July 2009, CERN was awarded an environmental label for its protection of rare flower species and the natural landscaping approach it has taken at its Meyrin site. The Laboratory has a very strict environmental policy: for years those in charge of CERN's green areas have given priority to natural management methods and have avoided the use of pesticides. In addition, patches of land are left unmowed in spring, allowing the local flora—especially the orchids—to grow naturally.

Since last year the team in charge of CERN's green areas within the GS-SEM-LS section has been turning its attention to the poplars. “During work for the first installations on the Meyrin site 50 years ago, people realised that there was a lot of water in the ground,” explains Mathieu Meylan, a member of the green-areas management team. “Poplars were planted because they absorb a lot of water from the ground and therefore provide good drainage.”

This tactic has worked and the site is now well drained. But these trees now pose a problem since they've reached the end of their life cycle (approximately 40 years) and are becoming fragile: when this happens, branches can fall off and a tree may even fall, representing a hazard to people and property. As Mathieu further explains: “In 2009, we commissioned institutions such as France’s National Forestry Office (ONF) and HEPIA in Switzerland to survey all the poplars on the Meyrin site.” The survey revealed that a substantial proportion of the remaining 400 trees were approaching the end of their life-cycle and needed to be replaced.”

Operations to cut down the poplars representing the greatest hazard will therefore start on Saturday, at 17 April on the car park in front of the entrance to the CERN kindergarten near Gate A as well as around the Cedars car park. To avoid all traffic disruption, the 33 poplars concerned will be cut down over three weekends, 11 each time. A second phase will start in November, bringing the total number of trees cut down to 75 by the end of the year. Replanting with varieties found locally will start in the winter.

Replanting operation on the terrace of Restaurant 1 (Thursday, 8 April 2010).

Timing is an all-important rule in nature
Mathieu points out that “For every tree that we cut down, we will plant one and in some cases two new trees. However, trees have to be planted at the right time of the year to take account of their growth cycle. We also have to take account of the cost. So we will plant relatively young trees, which are less expensive.” In addition, trees have to be replanted when they are resting, i.e. when there isn't much sap rising up the trunk. This means that replanting operations are restricted to the period between October and the end of April. “In December we will start planting wild and ornamental flowering cherry trees, red oaks, hornbeams and other varieties that are commonly found in this region.” Then we can just sit back and watch them grow!

Recycling idea
The trees that have been cut down will be transformed into wood chips for heating.

by CERN Bulletin