Pines and porcupines: a tree-ring analysis of browsing and dynamics of an overmature pine forest

Abstract

Past feeding activities of the North American porcupine (Erethizon dorsatum L.) in an overmature forest were reconstructed using tree-ring dated feeding scars on jack pine (Pinus banksiana Lamb.) trees in Parc national du Bic (Quebec). Following a long fire-free period, most pines that regenerated after the 1847 fire are currently senescent, moribund, or dead, and the youngest trees are nearly 100 years old. Balsam fir (Abies balsamea (L.) Mill.), the most abundant species in the regeneration layer, is predicted to replace jack pine given the absence of recent fire and present fire protection practices in the park. According to the age structure of feeding scars, porcupine activity has been particularly high during the 1980s, which is coincident with the creation of the park. Porcupine activity was lower before this decade and in the late 20th century and absent in this century (2000–2015). The recent decrease in the number of feeding scars is consistent with the decline of the porcupine population, as shown by censuses of active dens and inventories of individuals. Observed tree death is linked with tree senescence rather than excessive feeding. In the absence of fire, it is probable that the shift from the overmature pine stand to a balsam fir stand will profoundly affect porcupine activity. This research shows how the study of tree rings can unravel some of the ecological relationships structuring a forest ecosystem through fire, succession, and animal browsing.