Mineralization rates and factors influencing snag decay in four North American boreal tree species

The rate at which the wood of dead trees decays has numerous ecological implications. Decay rates of fallen tree boles have been extensively documented. However, decay rates of snags and the factors that influence decay in snags have received much less attention, especially in boreal species of eastern North America. In this study, mineralization rates (measured as wood density loss) were assessed in snags of four boreal species: trembling aspen (Populus tremuloides Michx.), balsam fir (Abies balsamea (L.) Mill.), jack pine (Pinus banksiana Lamb.), and black spruce (Picea mariana (Mill.) BSP). Wood density and variables potentially influencing decay rates (time since death, age, average radial growth, diameter at breast height, cerambycid larvae activity, and scolytid larvae activity) were measured on discs of 207 snags in northwestern Quebec, Canada. Mineralization rates varied significantly among species. Trembling aspen exhibited a more rapid rate of loss than conifers (k = 0.0274). Jack pine was the second most rapid species to lose wood density (k = 0.0152), followed by balsam fir (k = 0.0123). Black spruce was particularly resistant to mineralization (k = 0.0058), and its wood density was not significantly influenced by time elapsed since death for the time period sampled in this study. Time since death coupled with cerambycid larvae activity was associated with lower wood densities in trembling aspen, balsam fir, and jack pine, whereas slower growth was associated with a decreased mineralization rate in black spruce.