Swiss Forest Innovation: Trees Misted to Study Climate Adaptation

Deep within the Pfynwald forest, a surreal transformation is taking place. Rising sharply against the backdrop of the Valais Alps, 18 industrial scaffolding towers now dominate the canopy, turning an ancient ecosystem into a futuristic open-air laboratory. Standing a formidable 15 metres tall, these structures are not for construction, but for survival. They are the backbone of a groundbreaking experiment spearheaded by the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) and EPFL, designed to confront the harsh realities of climate change head-on.

This is not passive observation; it is active, high-stakes science. The towers are equipped with high-pressure nozzles that blast vapour over 60 specific Scots pines, creating a controlled microclimate in one of Switzerland's hottest and driest regions. At 615 metres above sea level, the Pfynwald is already a battleground for vegetation. Now, researchers are manipulating the very air these trees breathe to isolate the deadly effects of drought. "The goal is not to spray forests to save them, but to understand why a lack of water in the atmosphere has such a significant impact," declares project director Charlotte Grossiord, emphasizing the critical nature of this research.

Switzerland confronts a staggering projection: by 2060, summer rainfall will plummet by 25 percent. But the danger isn't just in the soil; it is in the air itself. Scientists are now racing to understand "Vapour Pressure Deficit" (VPD)—or simply, "thirsty air." As global temperatures soar, the atmosphere demands more moisture, stripping it aggressively from vegetation. This invisible enemy accelerates water stress, forcing trees to empty their reserves at an alarming rate.

Giovanni Bortolami, a key researcher on the project, illustrates the threat with a stark analogy: "Imagine a glass of water in a desert and a glass of water in a rainforest. The temperature is the same. The glass of water empties very quickly in the desert." This is the reality facing Swiss forests. The misting system in Pfynwald artificially reduces this atmospheric "thirst" by 20 to 30 percent, allowing scientists to compare misted trees against those left to battle the dry air alone. It is a race against time to quantify exactly how this atmospheric demand drives tree mortality before the climate shifts permanently.

The Pfynwald has been under the microscope since 2003, but this new phase elevates the research to a global level. While previous studies focused on soil irrigation—using translucent plastic to block rain or adding water to the ground—the current trial isolates the atmosphere as a distinct variable. It is a unique, dual-front approach: separating the impact of dry soil from dry air to pinpoint exactly what kills a tree.

The forest floor is now a web of cables and sensors. Devices hooked directly into tree trunks continuously monitor sap flow and diameter, providing real-time data on the trees' vital signs. This is critical monitoring for a forest that counts roughly 1,000 century-old Scots pines. The stakes are incredibly high; these trees are not just timber, they are carbon storage units. As Grossiord notes, understanding tree mortality is essential for estimating atmospheric carbon dioxide concentrations. Every tree that dies is a loss in the fight against greenhouse gases.

Running until 2028, this experiment is already yielding results that challenge conventional wisdom. While soil drought undeniably speeds up foliage dieback, preliminary data has thrown researchers a curveball: a dry atmosphere might actually slow down the dieback process in some contexts. This counter-intuitive finding suggests that trees may have complex, adaptive mechanisms to shut down and conserve resources when the air becomes too hostile.

These insights are vital for the future of Swiss forestry. As the country grapples with longer droughts and hotter summers, the data harvested here will dictate which species are planted for the next century. We are moving beyond conservation into strategic adaptation. The findings from the Pfynwald will not just explain why trees die; they will provide the blueprint for the forests of the future, determining how Switzerland's landscape will look for generations to come.