Abstract:

In recent years, forest areas in China increased largely thanks to afforestation. The plantation area accounts for 30% of the total forest areas of China. To understand the potential carbon sink of the plantation, CO₂ flux was measured continuously from 2006 and 2007 using the eddy covariance technique in a 30-year-old mixed plantation (Quercus variabilis, Robinia pseudoacacia and Platycladus orientalis) in a hilly area of the North China. The results showed inter-annual and seasonal variations of net ecosystem carbon exchange (NEE) were obvious. However, the diurnal variation was only remarkable in the growing seasons (from April to October). Daily NEE ranged from -27.1 to 8.1 g CO₂·m^-2d^-1 in 2006, and from -24.4 to 9.8 g CO₂·m^-2d^-1 in 2007. Monthly mean CO₂ uptake peaked in May in 2006 and in July in 2007. The magnitude of CO₂ uptake during the growing season accounted for about 96% of the whole year. Annual net carbon uptake in the plantation was 549.1 g C·m^-2a^-1 in 2006 and 445.4 g C·m^-2a^-1 in 2007. Carbon sink in the mixed plantation was notable and its inter-annual variation was significant. Drought in spring of 2007 was the main reason that led to a significant decrease in net carbon uptake in the mixed plantation.

Key words: mixed plantation, net ecosystem carbon exchange, eddy covariance