Fire disturbance during climate change: failure of postfire forest recovery on a boreal floodplain

Abstract

We used tree remains to document the failure of postfire forest recovery following a 1941 fire on a boreal floodplain along a third-order stream in northern Quebec. Two sites, one with postfire shrubs and the other an unburned forest, were studied. Tree remains on the floodplain and within the stream channel at the shrub site suggest the former presence of a forest stand similar to present-day vegetation at the forest site. At both sites, black spruce (Picea mariana (Mill.) BSP) has been the dominant tree species, whereas eastern larch (Larix laricina (Du Roi) K. Koch) and balsam fir (Abies balsamea (L.) Mill.) have made up only a small proportion of all living and dead stems. Sustained tree recruitment before the mid-19th century was followed by much reduced recruitment, in synchrony with the well-documented increasing trend of winter precipitation in northern Quebec. In combination with more frequent spring floods during the 20th century, the 1941 fire at the shrub site probably reduced the density of conifer stems, increased the abundance of shrubs, and excluded the fire-sensitive balsam fir and eastern larch. The fire also abruptly increased inputs of tree remains into the stream channel. Because of low establishment rate and slow growth of postfire conifers, forest recovery towards prefire tree density is unlikely under present-day conditions. Frequent fires in boreal landscapes, along with the anticipated increase of precipitation, suggest that some floodplains and associated streams may respond similarly to future climate change.