Switzerland: In Valais, we refresh the pines with misty

Under the heat of an end of spring, a multitude of nozzles mounted on scaffolding spray water vapor on the peaks of around sixty pines of sylvesters of fifteen meters in the Swiss region of Valais.

This essay conducted by the Federal Institute for Research on the Forest, Snow and the WSL Landscape and the Federal Polytechnic School of Lausanne (EPFL) is actually a unique experience in the world aimed at dissociating the effects of the dryness of the soil and that of air in a natural forest ecosystem, finished wood, one of the largest alpine pine -pine.

“The goal is not to spray the forests to save them but to understand why this lack of water in the atmosphere has such an important impact in the forests,” explains Charlotte Grossord, project manager, to AFP.

One of the purposes is to better understand the mortality mechanisms of trees because they form the basis of climatic models “which make it possible to estimate the concentration of CO2 in the atmosphere”, a greenhouse gas having a major role in global warming, underlines the professor in plant ecology.

The objective is also to help develop forestry strategies and the choice of the essences of the future, while in recent years, the frequency of dry summers has progressed in Switzerland. According to recent estimates from the Federal Environment Office, by 2060, it will fall up to 25% less rain in summer, and periods of drought will last longer.

The tests in finish wood also helps measure the speed of decline in trees and its impact on biodiversity, in order to better anticipate when other areas will be affected, explains Giovanni Bortolami, one of the researchers.

Located at 615 m above sea level, surrounded by alpine massifs, finish wood and its thousand centenary trees around the Rhône in one of the hottest and dry places in Switzerland, ideal conditions for researchers.

Since last year, foggers have appeared to study the dryness of air because climate change results in another disturbing environmental parameter: the increase in “thirst for air”.

“Imagine a glass of water in a desert and a glass of water in the tropical forest. The temperature is the same. The glass of water empties very quickly in the desert, but not in the tropical forest, ”says Mr. Bortolami.

It is “exactly the same on the trees” which will lose much more water “if the air is drier and which will, consequently,” consume the water of the ground faster “, continues the researcher in plant ecophysiology.

In the pine forest, 18 scaffolding towers with stairs were erected around the trees. High pressure nozzles diffuse water vapor in part of the canopy during the day to reduce this “thirst” of air by around 20 to 30%. The researchers then compare the data with the trees not having received this saving water vapor.

In the forest, large cables litter the ground. They connect sensors attached to the trees, to continuously measure the diameter of the trunks and the circulation of the sap – an indicator of water stress. Researchers also make measures directly on site every month. Experience will continue until 2028.

The first results show that the lack of water in the ground accelerates the decline process, a result which researchers expected.

“On the other hand, we have observed that a drying up of the atmosphere, rather than accelerating the decline, will slow it down. This is what really surprised us, ”says Ms. Grossord, who explains that the measurements show that with less water in the atmosphere, the trees close their stomates (pores) to keep their water resources.