EGU General Assembly 2020
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Can old growth alpine forests be biophysical barriers against current heat waves?

Leonardo Montagnani1, Nikolaus Obojes3, Gert Wolf4, and Glenda Garcia Santos4
Leonardo Montagnani et al.
  • 1Free University of Bolzano, Faculty of Science and Technology, Italy (
  • 3EURAC Research, Via Druso 1, I-39100, Bozen, Italy (
  • 4Alpen-Adria Universität Klagenfurt, 9020 Klagenfurt, Austria (

Can old growth alpine forests be biophysical barriers against current heat waves?

The current climate crisis requires an urgent understanding of ecosystem features dampening and alleviating the increasing radiation forcing. To this end, emission of latent heat from forests emerges with its relevance among the terrestrial ecosystem properties. It is not clear, however, if the different forest structures and ages act similarly, depending on the species composition, or if their structure has a role.

We performed a research on the hydrological cycle in the highly instrumented research facility in Renon forest, Italian Alps, belonging to the ICOS European infrastructure. The site is covered by a dense but structurally heterogeneous spruce forest, characterized by a young sector, with 30 years trees and an old forest sector composed by 200 years old trees.

Energy and water balance are quantified by eddy covariance instrumentation, 12 sap flux sensors in trees representative of the forest tree ages and 20 below-canopy pluviometers in each of the two forest structures. With these pluviometers, we quantified the relative role of canopy interception as a function of LAI density, precipitation intensity and duration. Water discharge and fog interception measurements allowed the closure of the water cycle at catchment scale.

Interestingly, we found that the water cycle is largely decoupled from the ground. In the old forest section, the fraction of water reaching the ground in the old sector is the 0.42±0.17 (vs. 0.67±0.17 in the young sector) of incoming precipitation. This suggests that in old alpine forests the hydrological cycle takes place largely in the crown and the old forest is using a large fraction of precipitation to dissipate heat.

Our results support the view of stand age as emerging property in the atmosphere-biosphere interaction and highlight the relevance of old forests in dampening the recurrent heat spells spreading across Europe, with the Alps and their remaining old growth forests standing as biophysical barriers.

How to cite: Montagnani, L., Obojes, N., Wolf, G., and Garcia Santos, G.: Can old growth alpine forests be biophysical barriers against current heat waves?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17882,, 2020

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Display material version 1 – uploaded on 04 May 2020
  • CC1: Comment on EGU2020-17882, Anke Hildebrandt, 06 May 2020

    I really like this comparison between the different sources for ET. I am confused about the energy source for ET. Are these summer conditions energy or water limited? Do you know how the overall surface energy balance evolve over those periods?

    • AC1: Reply to CC1, Leonardo Montagnani, 06 May 2020

      Dear Anke,

      Thank you for your interest in our study. I believe that the Renon site ET is mainly radiation limited, see Teuling et al.,  GEOPHYSICAL RESEARCH LETTERS, VOL. 36, L02404, doi:10.1029/2008GL036584, 2009. We have some 20 years of eddy covariance data from this site available, and I would welcome a possible your collaboration on this topic.


      Kind regards



  • AC2: Comment on EGU2020-17882, Leonardo Montagnani, 06 May 2020

    We have installed a passive fog collector at the ground in a large clearing and we collected the water resulting from the fog in a pluviometer. We know that this kind of measurements can be prone to systematic errors due to the large spatial heterogeneity of fog deposition, and having several fog collectors at different heights would be preferable, although not technically easy to implement.