Seasonal and Inter-Annual Variability in Net Ecosystem CO2 Exchange at Six Forest Flux Sites in Japan

1
LU-209 / ICDC7 Land Use and the Terrestrial
Carbon Cycle / September 28, 2005
Seasonal and Inter-Annual Variability in Net
Ecosystem CO2 Exchange at Six Forest Flux Sites
in Japan
Y. Ohtani1, Y. Yasuda1, Y. Mizoguchi1, T.
Watanabe1, Y. Nakai2, K. Kitamura2, S. Suzuki
1, K. Yamanoi2, T. Saito3, T. Morisawa3, Y.
Kominami4, T. Miyama4, Y. Goto4, T. Shimizu5
and K. Tamai5
1 Forestry and Forest Products Research
Institute (FFPRI) 2 Hokkaido Research Center,
FFPRI 3 Tohoku Research Center, FFPRI 4
Kansai Research Center, FFPRI 5 Kyushu Research
Center, FFPRI, Japan

• Contents
• Sites, Measurements and Data Processing
• Seasonal Changes in Observed Net Ecosystem
  Production (NEP) and Meteorological Factors
• Inter-Annual Variation in NEP
• Concluding Remarks

2
Deciduous forest Coniferous forest Mixed forest
Observation Sites
3
Measurement
CO2 Flux SAT DA-600-3T / KAIJO
(20cm span) IRGA Li-6262 / Li-Cor
(closed-path) Low-pass filter (24Hz cut
off) 510Hz Sampling, Recorded in MO
Tubing 3050m (6mm, teflon) Air sampling
rate Approx. 10Lmin-1 Water vapor
removed CO2 Storage Change IRGA Li-6262 /
Li-Cor 5 Levels below SAT
CO2 flux measurement system using closed-path gas
analyzer
4
Data Processing
Calculation of Fc Eddy covariance method (every
30 min) Lateral wind and vapor effects (Kimal
et al, 1968) Wind rotation (McMillen,1988)
WPL correction (Webb et al, 1980)
Compensation of CO2 delay Correction of CO2
flux dumping NEE Fc Sc Quality
Control Visual inspection for raw data QC
for raw data (Vickers Mahrt, 1997) u
selection for Fc
Parameterization for Gap-Filling
Semi-empirical parameterization (30 min)
Nighttime Re Exponential to Ta or Ts
Re a Q10 (Ta/10) Daytime Ag NEP Re
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Observed NEP and Estimated Ag and Re
Observed NEP and estimated gross assimilation
(Ag) and ecosystem respiration (Re). Ag and Re
are calculated by the parameterization used for
gap-filling at every 30 minutes. Daily sums are
plotted.
6
NEP and Meteorological Factors
Observed NEP (2002) indicated with air
temperature, short wave radiation and
precipitation (averaged over 5 days).
7
Monthly NEP and Its Inter-Annual variations
Observed monthly NEP for 4 years indicated with
air temperature, short wave radiation and
precipitation.
8
Annual NEP and Its Inter-Annual variations
Annual NEP, annual mean air temperature and
annual mean of daily short wave radiation. Red
and blue background colors indicate the maximum
and minimum NEP among the years.
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Observed Annual NEE to Latitude
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Concluding Remarks

• Tower flux measurement of CO2 was conducted in
  six forest sites in Japan.
• In the seasonal change, the maximum NEP was about
  1.5 2 times larger in the deciduous sites,
  although the growing period was about 2 2.5
  times longer in coniferous sites.
• The monthly NEP in the coniferous sites had
  inter-annual variation throughout the season, but
  the variation was only appeared from April to
  October in the deciduous sites.
• In the coniferous forests, the balance of
  assimilation and respiration induced by seasonal
  changes in solar radiation and air temperature
  seemed to be an important factor.
• In the deciduous broadleaved forest, solar
  radiation and the duration of the growing season
  are important factors with regards to annual NEP.
  
• The annual NEP had no clear relationships to
  annual mean Ta and Sd.
• NEP was obtained in six forest sites from 33 to
  43 N, ranged from 250 to 650 gCm-2y-1 .