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Zusammenfassung:
Climate extremes can have tremendous impacts on the terrestrial biosphere and their frequency is very likely
going to increase in the coming years. In this study we examine the impact of the 2015 summer heat wave on a
mountain grassland in the Western European Alps by jointly analyzing phenocam greenness (GCC) trajectories,
proximal sensing, CO2 flux data and structural canopy traits. Phenocam effectively tracked the impact of the heat
wave, showing 39% of reduction in maximum canopy greenness and a senescence advance of 32 days compared
to mean values. The same patterns (i.e. reduction of maximum values and senescence advance) were observed
for all considered canopy traits and photosynthetic ecosystem functional properties, in particular the maximum
light-saturated rate of CO2 uptake (Amax), LAI and PRI. Pixel-level analysis of phenocam images allowed us to
further highlight that forbs were more heavily impacted than grasses. Moreover the effect of the extreme event
on greenness seasonal course was evaluated testing new formulations of the Growing Season Index (GSI) model.
Results demonstrate that a combination of water and high temperature stress was responsible for the observed
reduction of canopy greenness during the heat wave.
