Alpine spring begins earlier, speeding up plant growth

Plants in the Alps are now springing to life sooner than they did just a few decades ago. A new study shows that over the past 25 years, vegetation in mountain regions has begun growing about six days earlier on average after snowmelt than it used to.

The research, led by Michael Zehnder of the WSL Institute for Snow and Avalanche Research SLF, points to a clear driver: rapid warming following the disappearance of seasonal snow.

Warming speeds up alpine spring

“On average, as a result of climate change, the ambient temperature is almost two degrees Celsius warmer after the disappearance of snow cover than it was 25 years ago,” Zehnder said.

The warmth accelerates growth, quickly turning snow-covered slopes into green alpine meadows. While that might seem like a small shift in timing, it marks a substantial change in the rhythm of alpine life.

“Climate change is reshaping mountain ecosystems,” Zehnder said. From flowers to farming, the pace of spring is picking up across elevations.

Alpine life feels the change

The changes in plant timing go beyond scientific curiosity. They touch various aspects of daily life in alpine regions.

For instance, “alpine farming might also start earlier in the future,” Zehnder noted, suggesting that warmer, greener pastures could prompt earlier seasonal grazing.

Hikers and tourists may also experience spring in the alpine region earlier than in past decades, potentially altering the timing of peak visitation.

But perhaps most consequential is what this shift could mean for alpine biodiversity. Some plants quickly respond to warm temperatures. Others rely on internal clocks or light levels, waiting for longer days before growing.

Some plants don’t begin growing right after the snow disappears. Some species wait for longer daylight, while others sprout quickly in response to rising temperatures.

Different clocks at different heights

The study uncovered important variation across elevations. Near the treeline, around 2,000 meters above sea level, vegetation required more cumulative warmth to begin growing when snowmelt came early.

In other words, the earlier the snow disappeared, the more warming days plants seemed to need before responding.

But higher up the slopes, plant communities showed more consistency. Even when snowmelt occurred early, these high-altitude plants appeared to rely on a fixed number of warm days before growth kicked in.

These subtle differences could have long-term consequences for how mountain vegetation evolves.

Species that respond quickly to warmth may expand their range or outcompete those tied more rigidly to other cues. Over time, that could change not only which plants dominate specific locations but also the entire structure of alpine ecosystems.

Monitoring the mountain spring

To measure these changes, Zehnder analyzed data from 40 stations that are part of the Intercantonal Measurement and Information System (IMIS), a Swiss weather and snow-monitoring network. Each station includes an ultrasonic sensor that tracks snow depth throughout the year.

“This way we receive data without having to be in the field ourselves,” Zehnder explained. Because those sensors work in summer, they detect subtle ground cover changes as snow melts and vegetation appears.

Zehnder used machine learning to train a model that distinguishes snow-covered ground from plant-covered ground using sensor data. With this model, he was able to pinpoint when each location made the transition from winter white to spring green over a 25-year period, from 1998 to 2023.

Still, to know which species were growing at the monitored sites, Zehnder had to go into the field himself. That meant trekking to remote IMIS stations at altitudes ranging from 1,700 to 2,700 meters above sea level.

“Researchers cannot tell from the IMIS station data which plants are growing under the sensors,” he noted, so direct observation was essential.

Climate picks the favorite plants

Zehnder emphasized that not all Alpine plant species will benefit equally from earlier snowmelt and rising temperatures.

“It’s important, though, to understand how different plant communities will have different responses to even earlier snowmelt in the future and who the winners and losers will be,” Zehnder said.

The shift in timing is likely to favor species that respond directly to warmth over those that wait for longer days. As these dynamics play out, the makeup of alpine meadows may transform, potentially reducing plant diversity in some locations.

Combining environmental data, fieldwork, and machine learning, the study reveals how climate change is shifting alpine life’s timing. With snow melting earlier and spring arriving sooner, the alpine region – like many of the world’s mountain ranges – are on the move.

The study is published in the journal Global Change Biology.

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