Influence of the substrate and ecosystem attributes on the decomposition rates of coarse woody debris in European boreal forests

• Wood decomposition rates depend on regional, forest stand and piece-scale factors.
• Regional temperature range affects the decomposition rate of CWD.
• Site moisture and canopy openness affect the decomposition rate at the forest stand scale.
• The CWD-piece scale predictors of decomposition rate are tree species and mortality mode.

Narrowing the uncertainties in coarse woody debris (CWD) decomposition rates depending on the ecosystem and substrate attributes can improve our understanding of biodiversity patterns and carbon dynamics in forest ecosystems. We estimated decomposition rates of aboveground CWD, represented by fallen and leaning logs, stumps and snags >8 cm in diameter sampled at eight sites in European boreal forests. In total, 3491 CWD pieces were sampled. The chronosequence period covered a range up to 168 years. Single exponential decomposition (mass loss) rates (k) averaged 0.066, 0.032, 0.027, and 0.014 year−1 for aspen (Populus tremula) and birch (Betula pendula, Betula pubescens), fir (Abies sibirica) and spruce (Picea abies, Picea obovata), Scots pine (Pinus sylvestris) and Siberian pine (Pinus sibirica), respectively. At the regional-scale, the decomposition rate decreased with increasing difference between maximum and minimum temperatures. The CWD decomposition rate was greater on open fertile sites with moderate moisture compared to rates on poor dry or moist sites under closed tree canopies. CWD tree species played the primary role in decomposition at the CWD-piece scale. CWD position and tree mortality mode were rate-controlling mainly for decomposition of fir and spruce CWD. CWD size did not affect decomposition rates. Our results predict CWD decomposition rates as a function of climatic factors, site conditions, tree species, stem position and mode of tree mortality in European boreal forests at the scale of regions, forest stands and individual CWD pieces.