Comparison of methods to quantify respirational carbon loss of coarse woody debris

Carbon (C) loss from coarse woody debris (CWD) may be important in forest ecosystem C budgets, yet there are no standard methods of quantifying it. Here we assessed respirational C loss of log segments of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.), to compare the two main measurement approaches (the static and dynamic methods using soda lime and an infrared gas analyser, IRGA) with three different measurement options for CWD logs. These included (i) incubation of the whole log segment, (ii) the use of small in situ chambers on the curved log surface, and (iii) extracted wedges of wood. On average, significantly higher amounts of CO(2) were measured with the IRGA (125%) compared with soda lime. In addition, the soda lime method requires careful calibration of incubation length and amounts of soda lime used. Regardless of the measurement method and tree species, substantially higher amounts of CO(2) were measured for whole log segments than for the other two options. Measuring respiration with small in situ chambers on logs or extracted wedges might underestimate real CO(2) flux by up to 74%. We therefore recommend measurement of CWD respiration using gas analysers for large log segments.