Ecosystems

An early start to the growing season doesn’t lead to a longer growing season in the Alps

Global warming is leading to longer growing seasons worldwide, with many plants growing earlier in spring and continuing longer in autumn thanks to warmer temperatures—so the general opinion. Now, however, plant ecologists at the University of Basel have been able to show that this is not the case for the most common type of alpine grassland in the European Alps, where an earlier start leads to earlier aging and leaves the grassland brown for months.

Spring 2022 was extremely warm, giving many plants an early start to the growing season. And the Swiss Alps were no exception, with the snow cover melting early and the underlying vegetation being quickly roused into growth. Researchers at the Department of Environmental Sciences at the University of Basel have investigated how such an early start affects the plants’ further development.

For their study, they removed intact blocks of alpine grassland and placed them in walk-in climate chambers at Basel’s Botanical Institute. Here, they left the vegetation to overwinter artificially in cold darkness, and then switched some of the blocks to summer conditions in February. A second group was left in the cold dark until April, before summer was introduced here as well. The researchers compared the growth and aging of these plants with their neighbors growing naturally at an elevation of 2,500 meters, which did not emerge from the snow until late June.

Tubs of grass with tubes in them set in the Swiss Alps. Some of the grasses in the tubs are notably browner than the natural grass in the photo.
Alpine plants that start to grow earlier also start to age earlier. as is the case with the alpine vegetation in these containers, which were exposed to summer weather several months before the snow melted (photograph taken in July). Photo: Patrick Möhl, University of Basel.

Our experiment more than doubled the available time for seasonal plant development and revealed an overarching autonomous control over growth and senescence. Whether the season was prolonged by two or four months, typical alpine summer conditions always initiated plant growth without major delay. However, early-onset of growth was accompanied by early-onset of senescence, halting above- and belowground plant growth even under ongoing, favourable summer conditions. Therefore, our findings challenge the widely assumed rise in future productivity as the thermal growing season prolongs due to climate warming.

Möhl et al. 2022.

Winter can come as quickly as August in the Alps, and there has been little incentive for plants to prepare for longer growing seasons. While the climate will make longer growing seasons possible, it will take a long while for the plants to adapt to take advantage of it. In their press release Möhl and colleagues add there is an additional problem. “Alpine grassland species reproduce primarily by vegetative means (clonally) and produce genetically identical relatives, which slows down the process of adapting to new environmental conditions through genetic change.”

It would appear that not all alpine grasslands will be in a position to make hay while the sun shines.

📰 The full press release is at Eurekalert.
🔬 Growth of alpine grassland will start and stop earlier under climate warming is available at Nature Communications.

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