PARENT SESSION
Poster Session 2: Forest Ecology
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

CO₂ flux over old temperate mixed forest in North- eastern China.

De-Xin, Guan ¹, ¹ Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, Liaoning, PR China

ABSTRACT- Eddy covariance measurements of carbon dioxide exchange were made above a temperate mixed forest for 16 month in northeastern China. The stand is a natural grown, unmanaged mixture of deciduous broad-leaved and coniferous forest and the trees cover a wide range of age classes with a maximum about 450 years. The objectives of this paper were to determine whether the so old forests are carbon sinks or source and to test the traditional hypothesis that forests at a comparatively late stage of development are insignificant as carbon sinks. The threshold of friction velocity (u*=0.2ms^-1 ) was empirically imposed according to nighttime measurements in fast growing season. The main results are that: (1) This forest was a carbon sink over the cross year, with 169 to 187gCm^-2 year^-1 during the measurement. (2) Net ecosystem exchange (NEE) in summer daytime was mainly controlled by photosynthesis active radiation (PAR) and the relation fits the Michaelis-Menten equation. Summer daytime NEE was also more loosely correlated to vapor pressure deficit (VPD) than PAR. But gross ecosystem production (GEP) was a little more closely correlated to VPD than NEE. (3) Diurnal course of NEE was varied with seasons. Amplitudes were large in fast growing period (June to August) and very small during winter (November to February). Even in the winter downward CO₂ flux was observed around the noon. (4) Net assimilation began in early May and ended at early September. Largest uptake occurred in June, then July and August. Large net CO₂ loose occurred in late September and October because relatively high temperature and defoliation of the most trees of the forest.

Key words: Net ecosystem exchange, Carbon dioxide, Eddy covariance, Old forest