Decomposition rates of coarse woody debris - A review with particular emphasis on Australian tree species

We reviewed the decay patterns and lifetimes (time to reach 95% mass loss) of coarse woody debris (CWD) on the forest floor. The objectives were to identify the factors influencing the decomposition process of CWD and to provide estimates of lifetimes for CWD from Australian tree species. This information is required for greenhouse accounting of forestry activities and land use change as well as the sustainable management of CWD in forest ecosystems. The analysis of a global data set on decay rates of CWD showed that, in particular, the mean annual temperature was a main driver of decomposition, accounting for 34% of the variation in decay rates. The Q₁₀, the factor by which biological processes accelerate when temperature increases by 10°C, was 2.53. Additional determinants of CWD decay rates were the initial density of wood and the diameter of logs. Median and average lifetimes derived from 184 decay rates were 49 and 92 years, respectively, which is considerably higher than the 10-year default for all litter proposed by the Intergovernmental Panel on Climate Change. The pattern of decay in most cases followed a negative exponential curve. To overcome the paucity of information on decomposition of CWD in Australian forests and woodlands, decay rates for a large number of species were derived from wood durability and decay resistance studies. For native Australian species, lifetimes ranged from 7 years in Eucalyptus regnans to 375 years in E. camaldulensis. The lifetimes for timber durability Classes 1-4 were 54, 39, 26 and 11 years, respectively, below 30° latitude and without the influence of termites. However, the experimental conditions under which durability and decay resistance are commonly determined are substantially different from the situation under which CWD decomposes in the field. These estimates must therefore be regarded as minimum lifetimes for CWD of most species. To determine decay rates of CWD with greater certainty, long-term field experiments in a wide range of ecosystems are required.