Effects of moisture, temperature and decomposition stage on respirational carbon loss from coarse woody debris (CWD) of important European tree species

Coarse woody debris (CWD) is critical for forest ecosystem carbon (C) storage in many ecosystems. Since the turnover of CWD is mostly driven by mineralization, changes in temperature and precipitation may influence its pools and functions. Therefore, we analysed, under controlled conditions, the effect of wood temperature and moisture on carbon respiration from CWD for the important European tree species Fagus sylvatica L., Picea abies (L.) Karst. and Pinus sylvestris L. in different stages of decay, represented by different wood densities. Additionally, we measured CWD respiration of individual F. sylvatica and P. abies logs over one year to analyse the effects of micro-climatic variables in the field. CWD respiration rates under controlled lab conditions were about two times higher for beech than for spruce and pine and similar for the latter two species. In addition, wood moisture exerted a stronger influence on respiration than wood temperature. In contrast, respiration in the field was most strongly controlled by temperature. Average Q(10) values under controlled conditions were 2.62 for F. sylvatica and 2.32 for P. abies across all temperature and moisture levels, while no significant relationship between temperature and CO2 flux was observed for P. sylvestris. About 80% of the variation in respiration under controlled conditions could be explained by species, wood density, moisture and temperature and their interactive effects. Temperature alone explained 96% (beech) and 94% (spruce) of the variation in respiration in the field. Furthermore, we predicted average monthly temperatures of CWD in the field very accurately from air temperature (r(2)=0.96), which is relevant for modelling CWD carbon dynamics under climate change scenarios. Our results indicate that species identity, decay stage and micro-climatic conditions should be considered when predicting CWD decay rates.