Carbon dioxide evolution rates for downed logs (coarse woody debris) and the forest floor were measured in a temperate, old-growth rain forest in Olympic National Park, Washington, using the soda lime trap method. Measurements were taken every 4 weeks from October 22, 1991, to November 19, 1992. Respiration rates for Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) and western hemlock (Tsugaheterophylla (Raf.) Sarg.), logs were determined for decay classes 1–2, 3, and 5 in two diameter classes. Overall, western hemlock logs respired at a rate 35% higher (4.37 g CO 2 •m −2 •day −1 ) than Douglas-fir logs (3.23 g CO 2 •m −2 •day −1 ). Respiration rates for decay class 1–2 logs of both species were similar to decay class 5 logs (4.46 and 4.07 g CO 2 •m −2 •day −1 , respectively), but decay class 3 logs respired at a lower rate (3.23 g CO 2 •m −2 •day −1 ). Seasonal patterns of respiration rates occurred, particularly for decay class 1 and 2 western hemlock logs where monthly averages ranged from a low of 2.67 g CO 2 •m −2 •day −1 in February 1992 to a high of 8.30 g CO 2 •m −2 •day −1 in September 1992. Rates for decay class 1–2 western hemlock logs were greater than those from the forest floor, which ranged from 3.42 to 7.13 g CO 2 •m −2 •day −1 . Respiration rates were depressed in late July and August compared with fall and spring owing to the summer drought characteristic of the Pacific Northwest. Large-diameter western hemlock logs in decay class 1–2 had higher respiration rates than small-diameter logs, whereas large-diameter decay class 3 western hemlock logs had lower respiration rates than small-diameter logs.
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Marra et al. (1994) studied this question.