CO2 Fluxes at high-altitude mountain ecosystems: a comparative study of two grasslands in the Aosta valley

Mountain ecosystems are highly sensitive to the impacts of climate change. Nevertheless, our knowledge of critical biogeochemical processes—key to understanding how these ecosystems cope to shifting environmental conditions—remains limited.

This study examines and compares carbon dioxide (CO₂) turbulent flux measurements, obtained through the eddy covariance (EC) method at two Italian high-altitude sites: Torgnon and Nivolet in the Western Alps. These sites, part of the ICOS (Integrated Carbon Observatory System) network as Associated stations IT-Tor (Torgnon) and IT-Niv (Nivolet), are unmanaged subalpine grasslands situated at elevations of 2050 m and 2750 m, respectively, with different plant species compositions. Snow typically covers these areas from late October to late May at IT-Tor and until June at IT-Niv, restricting the growing season to approximately four to five months. Continuous EC measurements of CO₂ fluxes have been conducted continuously since June 2017 at IT-Tor and since June 2019 at IT-Niv.

This work focuses on comparing CO₂ fluxes from both sites under comparable meteorological conditions to explore the differences between the two canopies from an ecophysiological perspective. Additionally, phenological patterns are analyzed to evaluate how each grassland responds to extreme weather events, including the 2022 summer drought, the most severe drought event recorded in the last 17 years.

Our results emphasize the sensitivity of mountain ecosystems to climate change and highlight the importance of continuous monitoring to better understand and manage these fragile environments. The ecophysiological responses of these two mountain ecosystems to varying environmental conditions will be discussed considering their different altitude, species composition, and historical management.

Further research, combining long-term data with advanced modeling approaches, will be crucial for developing a more comprehensive understanding of how climate extremes affect mountain ecosystems across Europe.