ICOS Science Conference, Session 8

1. ||
Placeholder for organisational unit name / logo
(edit in slide master via “View” > “Slide Master”)
Ecosystem functioning and recovery after two consecutive
extreme years in Switzerland
Mana Gharun, Ankit Shekhar, Lukas Hörtnagl, Susanne Burri, Werner Eugster, Nina Buchmann
Grassland Sciences, ETH Zürich
116.09.2020ICOS Conference

2. ||
Placeholder for organisational unit name / logo
(edit in slide master via “View” > “Slide Master”)
2
• Areas affected negatively in 2018 in Europe 1.5 times larger than in 2003 (Buras et al. 2020)
• In Switzerland 2019 and 2018 were the 3rd and 4th warmest years since the start of the measurements in 1864 (MeteoSwiss 2020)
2018 and 2019 extreme years
(Source: SwissSMEX 2018) (Source: MeteoSwiss 2018)
Precipitation anomaly (%)
Temperatureanomaly(%)
16.09.2020ICOS Conference

3. ||
Placeholder for organisational unit name / logo
(edit in slide master via “View” > “Slide Master”)
3
Swiss FluxNet – Network of long-term eddy covariance flux measurements
16.09.2020ICOS Conference

4. ||
Placeholder for organisational unit name / logo
(edit in slide master via “View” > “Slide Master”)
Site overview
4
Davos
• 1639 m a.s.l.
• Mean precipitation 1046 mm and mean T 3.5 °C
822 mm and 4.2 °C (1997-2019)
• Picea abies
• Tree age up to 370 years
• Continuous measurements since 1997
Lägeren
• 682 m a.s.l.
• Mean precipitation 830 mm and mean T 7.4 °C
828 mm and 8.5 °C (2005-2019)
• Fagus sylvatica, Fraxinus excelsior, Acer
pseudoplantanus, Abies alba, Picea abies
• Tree age up to 170 years
• Continuous measurements since 2004
16.09.2020ICOS Conference
Davos (CH-Dav) coniferous forest (ICOS Class 1)Lägeren (CH-Lae) mixed deciduous forest

5. ||
Placeholder for organisational unit name / logo
(edit in slide master via “View” > “Slide Master”)
5
Post-processing of the eddy covariance measurements
REddyProc package in R (Wutzler et al. 2018):
 Dynamic u* filtering
 Gap filling with the Marginal Distribution Sampling method
(Reichstein et al. 2005)
 LUT created from SW_IN, Tair, VPD
 Mean Diurnal Course
 Nighttime partitioning method (Reichstein et al. 2005)
 Best and medium quality data used
2020
2016
2012
2008
2004
2000
6 12 18
Net Ecosystem Exchange (NEE, µmol m-2 s-1)
16.09.2020ICOS Conference

6. ||
Placeholder for organisational unit name / logo
(edit in slide master via “View” > “Slide Master”)
6
Long-term net ecosystem exchange (NEE)
Mixed forest - Lägeren Coniferous forest - Davos
16.09.2020

7. ||
Placeholder for organisational unit name / logo
(edit in slide master via “View” > “Slide Master”)
7
Changes in long-term net ecosystem exchange partitioning
Flux (gC m-2 s-1)
1 Error bars mark the 95% confidence interval
2 Number of years for each uptake period n = 5
3 GPP = Gross primary productivity, Reco = Ecosystem respiration
16.09.2020ICOS Conference
Flux (gC m-2 s-1)
Mixed forest - Lägeren Coniferous forest - Davos

8. ||
Placeholder for organisational unit name / logo
(edit in slide master via “View” > “Slide Master”)
8
Atmospheric and soil dryness in 2018 and 2019
1 Soil water deficit index estimated following Martínez-Fernández et al. (2015) within the soil top 5 cm 16.09.2020ICOS Conference
Coniferous forest - DavosMixed forest - Lägeren

9. ||
Placeholder for organisational unit name / logo
(edit in slide master via “View” > “Slide Master”)
9
Diel cycles of gross primary productivity (GPP)
16.09.2020ICOS Conference
Mixed forest - Lägeren Coniferous forest - Davos

10. ||
Placeholder for organisational unit name / logo
(edit in slide master via “View” > “Slide Master”)
10
Midday depression in evapotranspiration (ET)
16.09.2020ICOS Conference
Mixed forest - Lägeren Coniferous forest - Davos

11. ||
Placeholder for organisational unit name / logo
(edit in slide master via “View” > “Slide Master”)
11
Gross primary productivity response to climate
Solarradiation(Wm-2)
GPP (µmol CO2 m-2 s-1)
Vapor pressure deficit (hPa)
16.09.2020ICOS Conference
Vapor pressure deficit (hPa)
Mixed forest - Lägeren Coniferous forest - Davos
GPP (µmol CO2 m-2 s-1)

12. ||
Placeholder for organisational unit name / logo
(edit in slide master via “View” > “Slide Master”)
12
Ecosystem respiration response to climate
Soil water content (%)
Reco (µmol CO2 m-2 s-1)
Airtemperature(°C)
16.09.2020ICOS Conference
Soil water content (%)
Reco (µmol CO2 m-2 s-1)
Mixed forest - Lägeren Coniferous forest - Davos

13. ||
Placeholder for organisational unit name / logo
(edit in slide master via “View” > “Slide Master”)
13
Ecosystem underlying water use efficiency (WUEu) response to drought
16.09.2020ICOS Conference
𝑊𝑈𝐸 𝑢 =
𝐺𝑃𝑃 𝑉𝑃𝐷
𝐸𝑇
Mixed forest - Lägeren Coniferous forest - Davos
1 Drought period in spring is 15 April – 15 May and in summer 15 July – 15 August

14. ||
Placeholder for organisational unit name / logo
(edit in slide master via “View” > “Slide Master”)
14
Summary
• Atmospheric and soil dryness larger in 2018 (than in 2019) in the low-elevation mixed forest (Lägeren), but larger
in 2019 in the high-elevation coniferous forest (Davos)
• Larger reductions in net ecosystem exchange in the low-elevation forest during drought than in the high-elevation
forest
• Significant differences in winter precipitation between 2018 and 2019  increase in spring productivity in 2018
but decrease in 2019 in the high-elevation forest
• Overall 2019 and 2018 similar effect on ecosystem net CO2 uptake
• Long-term changes in net ecosystem exchange due to increased respiration in the high-elevation forest but
decreased productivity in the low-elevation forest
• Stronger physiological response to drought in the coniferous forest
• Larger increase in water use efficiency of the coniferous forest in response to drought (but no significant increase
in 2019).
Thank you for your attention!
16.09.2020ICOS Conference