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Carbon dioxide (CO2) flux from coarse woody debris is an important source of carbon emission in forests with large amounts of coarse woody debris (CWD). Respiration from downed logs of Korean pine (Pinus koraiensis Sieb. et Zucc.) and Amur linden (Tilia amurensis Rupr.) and their response to meteorological factors were investigated using the closed static chamber-gas chromatography technique in an old-growth temperate forest in Changbai Mountain region, north-eastern China. On a yearly timescale, daily respiration rates (R log) varied over two orders of magnitude (8.7-252.3 mg Ckg-1), and were significantly correlated with wood water content and temperature (p<0.05). The temperature-dependent empirical exponential models for each decay class explained more than 67% of the observed variations in R log. More decayed wood had a greater water content and pore space than less decayed wood, and these differences were probably responsible for the observed difference in respiration rate among decay classes. The annual carbon loss rate due to respiration was estimated to be 28.0±3.7 g Cm-2, which contributed only about 3% of total carbon loss from forest floor, but net carbon flux from downed logs accounted for up to 15% of net ecosystem exchange in this old temperate forest. Downed logs represent a small, but substantial carbon flux that is expected to increase over the next several decades in old-growth forest. [ABSTRACT FROM AUTHOR]