Grünwald, Thomas: Windthrow turns a former old spruce forest into a net CO2 source for 11 years

Windthrow turns a former old spruce forest
into a net CO2 source for 11 years
Faculty of Environmental Sciences Institute of Hydrology and Meteorology, Chair of Meteorology

Windthrow turns a former old spruce forest into a net CO2 source for 11 years
TU Dresden - Meteorology / Thomas Grünwald
ICOS Science Conference // 14.09.2022
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o as a consequence of more frequent climate extremes (drought,
windthrow, beetle infestation) an increase in damaged forests is
expected
o leads to a loss of C sinks and additional C sources in affected areas
for several years
o to quantify the related C budgets against the background of a typical
forest C sink, parallel monitoring of CO2 fluxes of a managed old
spruce forest and a young mixed oak forest after a larger windthrow
in 2007 (formerly old spruce forest) in East Germany have been
implemented in 2010
Background / Motivation

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ICOS ecosystem sites in Saxony

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class 1 (old spruce)
assoc. (cropland)
assoc. (permanent pasture)
cand. (young oak)
DE-Tha
old spruce
 EC start 1996
DE-Hzd
old spruce until 2006
windthrow Jan 2007 (Kyrill)
oak planting 2007/2008
 EC start 2010
distance 5.3 km

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DE-Tha
2010 2022
EC: GILL R3-50 / Licor LI-7000 EC: GILL R3-50 / Licor LI-7000
GILL HS-50 / Licor LI-7200

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DE-Hzd
2010 (3 years after windthrow) 2022 (15 years after windthrow)
EC: Campbell CSAT3 / Licor LI-7500A

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DE-Tha DE-Hzd
Altitude (m a.s.l.) 385 395
MAT (°C) 1959 – 2021 8.1 7.7
MAP (mm a-1) 1959 – 2021 829 867
MAR (W m-2) 2010 – 2021 131 123
Canopy height (m) 31 9.5
Stand age (years) 118 15
Stand density (n ha-1
) 220 ~ 9000
Site and stand characteristics

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Site and stand characteristics
Water availability
Soil moisture DE-Hzd >> DE-Tha
Decreasing trend during the dry years
2018 – 2020 and 2022
Minimum soil moisture DE-Tha < 5 Vol-%

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DE-Tha DE-Hzd
Spike removal (Mauder et al., 2013) x x
Automatic time lag optimization x x
Axis rotation:
Planar fit (Wilczak et al., 2001)
x x
Density fluctuations:
Converting concentrations into mixing ratios
x x
Density fluctuations:
Instrument sensible heat (LI-7500)
x
Quality check (Mauder and Foken, 2004) x x
Spectral correction
High-pass filtering correction (Moncrieff et al., 2004)
x x
Spectral correction
Low-pass filtering correction (Fratini et al., 2012)
x x
Spectral correction
Instrument separation (Horst and Lenschow, 2009)
x x
EC data processing
EddyPro® v6.x.x and EddyPro® v7.x.x

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DE-Tha
NEP
+16.3 tCO2 ha-1 a-1
(2010 – 2021)
-15.6 tCO2 ha-1 a-1
(2010 – 2016)
DE-Hzd
NEP
+2.9 tCO2 ha-1 a-1
(2018 – 2021)
Results Annual CO2 budgets

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Cumulated loss
of carbon fixation
24 tCO2 ha-1 a-1
or
288 tCO2 ha-1
(2010 – 2021)
Assuming DE-Hzd
would have act as
CO2 sink of
an old spruce forest
like DE-Tha
without disturbance

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DE-Tha
GPP
57.1 tCO2 ha-1 a-1
(2010 – 2021)
GPP
40.6 tCO2 ha-1 a-1
(2010 – 2014)
DE-Hzd
GPP
55.1 tCO2 ha-1 a-1
(2015 – 2021)

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DE-Tha
TER
+40.8 tCO2 ha-1 a-1
(2010 – 2021)
DE-Hzd
TER
57.5 tCO2 ha-1 a-1
(2010 – 2021)

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Results Cumulative CO2 budgets
01.01.2010
01.01.2011
01.01.2012
01.01.2013
01.01.2014
01.01.2015
01.01.2016
01.01.2017
01.01.2018
01.01.2019
01.01.2020
01.01.2021
01.01.2022
-150
-100
-50
0
50
100
150
200
250
-150
-100
-50
50
100
150
200
250
0
-14.8 tCO2 ha-1
a-1
(2010 - 2017)
+2.6 tCO2 ha-1
a-1
(2018 - 2021)
crop rotation (Saxony)
permanent pasture (Saxony)
wetland (Western Pomerania)
oak plantation (Saxony)
+9.5 tCO2 ha-1
a-1
-1.3 tCO2 ha-1
a-1
+20.4 tCO2 ha-1
a-1
CO
2
source
+11.3 tCO2 ha-1
a-1
pine (Brandenburg)
spruce (Tharandter Wald)
spruce (Eastern Ore Mountains)
alder (Spreewald)
CO
2
sink
+3.9 tCO2 ha-1
a-1
+2.5 tCO2 ha-1
a-1
Net
CO
2
exchange
in
tCO
2
ha
-1
(cumulative)
+16.9 tCO2 ha-1
a-1
Forest
Agriculture
Wetland
Disturbance

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o parallel CO2 flux monitoring at a windthrow site (formerly old spruce)
and an old spruce site reveal the duration and amount of C loss at
the disturbed site as well as the difference in C sinks after returning
of DE-Hzd to a moderate C sink
o DE-Hzd switched to a net CO2 source for 11 years (2007 – 2017)
o The moderate CO2 sink at DE-Hzd from 2018 to 2021 is only 21% of
DE-Tha
o The cumulative C loss at DE-Hzd is 288 tCO2 ha-1 for the 12 year
period 2010 – 2021
o Similar CO2 sources of 12.8 tCO2 ha a-1 reported for a clearcut near
DE-Wue during 4 years after disturbance
Ney et al., 2019. CO2 fluxes before and after partial deforestation of a Central
European spruce forest. Agricultural and Forest Meteorology, 274, 61-74.
Conclusions

Grünwald, Thomas: Windthrow turns a former old spruce forest into a net CO2 source for 11 years

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