Forest succession rate and pathways on different surface deposit types in the boreal forest of northwestern Quebec

Forest stands within the Quebec-Ontario paludification-prone Clay Belt are expected to converge to open unproductive black spruce (Picea mariana) stands regardless of initial tree composition with the prolonged absence of fire. We hypothesized that different surface deposits would display different stand transition characteristics, as recent research on the deglaciation history of the regions suggests that certain site conditions could exhibit different susceptibility to paludification. We quantified the rate and age of transitions of different succession stages for various surface deposits using a large spatio-temporal forest database. Our results suggest that a complete convergence to open and less productive black spruce stands can occur, but it may take a long time (i.e., more than 500 y), especially on surface deposits less prone to paludification, such as coarse-textured soils. We also observed that if succession pathways start with open and less productive black spruce stands, their capacity to change to more productive stands is conditioned by the surface deposit. Consequently, based on preferential age of transition, transition rates, and succession pathways, we suggest an increased susceptibility to paludification as one goes from coarse-textured deposits to fine-textured deposits and finally to restructured clay deposits, which are regionally designated as Cochrane Till. In terms of forest management, surface deposit susceptibility to paludification should be taken into account in order to minimize soil organic accumulation and the loss of tree productivity.