16 May 2024

Mountain meadows are threatened by climate change

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Rising temperatures drive the loss of humus in mountain meadows and, with it, the release of CO2 into the atmosphere. This is reported in a study by the Technical University of Munich

by Matteo Cavallito

 

Climate change reduces humus content and nitrogen reserves in alpine meadows by altering soil structure. In this context, some practices such as organic fertilization, for example, can compensate for the loss of these elements but only partially. This is reported in a study by the Technical University of Munich (TUM).

The study

“Studying soil responses to climate change in detail helps us to better understand the long-term effects on alpine grassland ecosystems,” explains Noelia Garcia-Franco, a TUM researcher and co-author of research conducted on several areas in the Bavarian districts of Weilheim-Schongau and Garmisch-Partenkirchen.

Scientists made several mesocosms – that is, units containing soil samples used as miniature ecosystems – to assess the influence of climate on soil and plants.

The mesocosms were moved from some places located at higher altitudes to others placed lower down, thus experiencing a maximum warming of three degrees Celsius. Half of the mesocosms were grown intensively, half extensively. That means, in other words, the meadows were mowed more often and fertilized more. Soil samples were collected after four years.

Soils lose up to 22% of their humus

Results showed that temperature increases dramatically reduced humus content in fields under extensive management: minus 22% with a 3°C increase and minus 14% with a 2°C increase. With intensive management, the loss of humus in meadows was only slightly less -11%. Also reducing, the scholars noted, was the nitrogen content, a key soil nutrient.

For both management practices, the loss of soil organic carbon was mainly associated with a decrease in large clods.

The study, in particular, “provides evidence that simulated climate change induced a rapid and substantial decline of soil organic carbon in mountainous, organic carbon-rich grassland soils, which may be attributed to decreased physical organic carbon protection within large macroaggregates.”

Mountain meadows are shrinking

The survey thus highlights the heavy burden of climate change, which, the authors note, is becoming more intense in the mountainous regions of central and northern Europe than in other areas. Indeed, since the 1980s, the average annual temperature in the Alps has increased by two degrees. The higher temperatures increase the activity of soil microorganisms. As a result, humus is broken down more rapidly and released as CO2.

Mountain meadows, the authors say, maintain a wide biodiversity and constitute “one of the largest reservoirs of soil-bound organic carbon in Central Europe.” However, their presence is declining. According to some estimates, the European Union has lost 16 percent of its grasslands since 1969. In the Italian Alps, the situation is even worse: minus 45 percent in 50 years. Changing agricultural patterns and heavy urbanization, in this sense, have been the determining factors.