1. Seasonal and Inter-Annual Variability in Net Ecosystem CO 2 Exchange at Six Forest Flux Sites in Japan Y. Ohtani* 1, Y. Yasuda* 1, Y. Mizoguchi* 1, T. Watanabe* 1, Y. Nakai* 2, K. Kitamura* 2, S. Suzuki * 1, K. Yamanoi* 2, T. Saito* 3, T. Morisawa* 3, Y. Kominami* 4, T. Miyama* 4, Y. Goto* 4, T. Shimizu* 5 and K. Tamai* 5 *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 LU-209 / ICDC7 Land Use and the Terrestrial Carbon Cycle / September 28, 2005 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. Observation Sites LU-209 / Seasonal and Inter-Annual Variability of NEP in Japan / Y.Ohtani et al. Deciduous forest Coniferous forest Mixed forest

3. Measurement CO 2 Flux: SAT: DA-600-3T / KAIJO (20cm span) IRGA: Li-6262 / Li-Cor (closed-path) Low-pass filter (24Hz cut off) 5~10Hz Sampling, Recorded in MO Tubing: 30~50m (6mm, teflon) Air sampling rate: Approx. 10Lmin -1 Water vapor removed CO 2 Storage Change: IRGA: Li-6262 / Li-Cor 5 Levels below SAT CO 2 flux measurement system using closed-path gas analyzer LU-209 / Seasonal and Inter-Annual Variability of NEP in Japan / Y.Ohtani et al.

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 CO 2 delay ; Correction of CO 2 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 Q 10 (Ta/10) Daytime: Ag = NEP + Re

5. LU-209 / Seasonal and Inter-Annual Variability of NEP in Japan / Y.Ohtani et al. 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. LU-209 / Seasonal and Inter-Annual Variability of NEP in Japan / Y.Ohtani et al. NEP and Meteorological Factors Observed NEP (2002) indicated with air temperature, short wave radiation and precipitation (averaged over 5 days). Soil: andosol

7. LU-209 / Seasonal and Inter-Annual Variability of NEP in Japan / Y.Ohtani et al. Monthly NEP and Its Inter-Annual variations Observed monthly NEP for 4 years indicated with air temperature, short wave radiation and precipitation.

8. LU-209 / Seasonal and Inter-Annual Variability of NEP in Japan / Y.Ohtani et al. 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.

9. 3035 Our results ranged: NEE (gC m -2 y -1 ) Deciduous (NEE) Coniferous (NEE) Mixed (NEE) Ronald (1998) Added to Ronald (1998) Latitude (North) LU-209 / Seasonal and Inter-Annual Variability of NEP in Japan / Y.Ohtani et al. Observed Annual NEE to Latitude

10. LU-209 / Seasonal and Inter-Annual Variability of NEP in Japan / Y.Ohtani et al. Concluding Remarks Tower flux measurement of CO 2 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 -2 y -1.