Impact of seed and seedling predation by small rodents on early regeneration establishment of black spruce

Black spruce (Picea mariana (Mill.) BSP) postdispersal seed and juvenile seedling predation by small rodents (Peromyscus maniculatus (Wagner), Clethrionomys gapperi (Vigor), and Phenacomys intermedius (Merriam)) was assessed in three boreal habitats over a 2-year period using an extensive exclosure-control experiment. Small rodent relative abundance was measured during six periods using snap trapping. We found that seed and juvenile seedling predation by small rodents varied according to habitat type and over time. Indeed, seed predation was higher in spruce-moss forests than in other habitats, notably during the winter of 2002. During this period, seedling predation was higher in recent burns. This period of higher seed and juvenile seedling predation corresponded to an increase in small rodent abundance in our study area. We suggest that seeds and juvenile seedlings can become important food sources for small rodents during winter when fresh and succulent vegetation is rare, as shown by results of seed predation. The impact of small rodents on the early regeneration of black spruce in the eastern Canadian boreal forest is thus an important factor to consider to better understand the forest regeneration process in this particular biome. Rodents can have a major effect on regeneration following a burn and can also contribute to poor seedling establishment from natural seed rain under mature cover.