Litter decomposition rates in Canadian forests

The effect of litter quality and climate on the rate of decomposition of pl ant tissues was examined by the measurement of mass remaining after 3 years ' exposure of 11 litter types placed at 18 forest sites across Canada. Amon gst sites, mass remaining was strongly related to mean annual temperature a nd precipitation and amongst litter types the ratio of Klason lignin to nit rogen in the initial tissue was the most important litter quality variable. When combined into a multiple regression, mean annual temperature, mean an nual precipitation and Klason lignin:nitrogen ratio explained 73% of the va riance in mass remaining for all sites and tissues. Using three doubled CO2 GCM climate change scenarios for four Canadian regions, these relationship s were used to predict increases in decomposition rate of 4-7% of contempor ary rates (based on mass remaining after 3 years), because of increased tem perature and precipitation. This increase may be partially offset by eviden ce that plants growing under elevated atmospheric CO2 concentrations produc e litter with high lignin:nitrogen ratios which slows the rate of decomposi tion, but this change will be small compared to the increased rate of decom position derived from climatic changes.