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Temporal and spatial variations in the seasonal patterns of CO₂ flux in boreal, temperate, and tropical forests in East Asia

Saigusa, Nobuko, Yamamoto, Susumu, Hirata, Ryuichi, Ohtani, Yoshikazu, Ide, Reiko, Asanuma, Jun, Gamo, Minoru, Hirano, Takashi, Kondo, Hiroaki, Kosugi, Yoshiko, Li, Sheng-Gong, Nakai, Yuichiro, Takagi, Kentaro, Tani, Makoto, Wang, Huimin
Agricultural and forest meteorology 2008 v.148 no.5 pp. 700-713
primary productivity, boreal forests, temperate forests, seasonal variation, gas emissions, vapor pressure, water vapor, carbon dioxide, dry season, solar radiation, tropical forests, air temperature, spatial variation, geographical variation, growing season, Mongolia, Thailand, Siberia, Japan, China, Malaysia
Measurements of net ecosystem production (NEP) over forest stands were conducted from 11 flux towers in sub-arctic, temperate, and tropical regions in East Asia between 2000 and 2005. The sites extend over a wide latitude, ranging from 3 to 64°N, and include sub-arctic and temperate needle-leaf deciduous forests (larch) (central Siberia, Mongolia, China, and northern Japan), temperate mixed, broadleaf deciduous, needle-leaf evergreen forests (northern and central Japan), and seasonal and tropical rain forests (Thailand and Malaysia). The sub-arctic larch forests had short growing periods of 3-4 months. The temperate deciduous forests showed the greatest positive NEP after leaf expansion in early summer. Among the 11 sites, the maximum gross primary production (GPP) was observed in a temperate larch forest during the early stages of the growing period due to the high productivity of the larch species. The temperate evergreen sites displayed positive NEP earlier in the spring than the deciduous sites and had long growing periods (>10 months). The tropical seasonal forests showed negative NEP during the dry period from February to April, and turned positive after the rainy season started. The tropical rain forest showed a small flux (<30gCm⁻² month⁻¹) throughout the year without a clear seasonal change. In 2002 and 2003, several significant weather anomalies were observed, such as increased temperature in the temperate sites and less precipitation than average in the tropical sites in the beginning of 2002, and decreased solar radiation in the temperate sites in the 2003 summer. The seasonal patterns of NEP were sensitive to the anomalies, and the variations were caused by: (1) high spring air temperature, which induced an early start of the growing period in the temperate forests, (2) summer solar radiation, which controlled the summer GPP in the temperate forests with a slight variation among sites due to different responses of GPP to the temperature and water vapor pressure deficit (VPD) conditions, and (3) a long dry season, which significantly reduced GPP in a tropical seasonal forest. The dataset, which was obtained from a wide variety of forest ecosystems in East Asia over several years, is essential to validate ecosystem models and to generate technological developments of satellite remote sensing in the distribution of the terrestrial carbon budget in Asia.