Long-term forest floor carbon dynamics after fire in upland boreal forestsof western Canada

We examined the long-term dynamics of upland boreal forest floors after dis turbance by fire. We selected two important and contrasting upland tree spe cies, Pinus banksiana (jack pine) and Populus tremuloides (trembling aspen) , in three distinct climatic zones across the boreal forest of western Cana da, and sampled 80 fire-originated stands divided into six chronosequences with ages ranging from 14 to 149 years. The forest floor was a large compon ent of carbon storage. Averaged across ages and zones, it was 1.31 and 2.78 kg C m(-2) for P. banksiana and P. tremuloides, respectively, compared wit h 4.03 and 5.56 kg C m(-2) in aboveground trees. These data exclude decompo sing coarse woody debris, which was a significant component of the forest f loor (0.18/0.13 kg C m(-2)) and requires further study. The contributions f rom shrubs (0.035/0.151 kg C m(-2)), ground vegetation (0.019/0.026 kg C m( -2)), and moss-plus-lichen (0.179/0.004 kg C m(-2)) were relatively small. An analysis of covariance (ANCOVA) model showed that forest floor carbon wa s positively related to stand age, as well as being affected by species and climatic zone. Much of the variability was explained by species, and speci es-specific regression models showed that for P. tremuloides forest floor c arbon was strongly related to stand age, mean annual temperature, and mean annual precipitation, and for P. banksiana, forest floor carbon was strongl y related to an index of moss dominance. The regression models suggest that the forest floor carbon pool in upland forests of the western Canadian bor eal will be sensitive to climate change, but this sensitivity would need to be tested with process-based models.