Growth dynamics of black spruce in stands located between the 51st and 52nd parallels in the boreal forest of Quebec, Canada

Despite their ecological importance, the role and effects of insect outbreaks on stand dynamics of the northern boreal forests in North America have still to be demonstrated. The study was conducted between the 51st and 52nd parallels in Quebec, Canada, to identify mechanisms governing regeneration of high-latitude stands by investigating variations in growth of trees during stand development. Chronologies of tree-ring width and individual dynamics of growth in height and volume were assessed in black spruce (Picea mariana (Mill.) B.S.P) of one even-aged and five uneven-aged stands. Uneven-aged stands contained trees up to 340 years old and representing almost every age class. Several growth reductions were observed that were synchronized between stands and were characterized by high amplitudes but different percentages of affected trees. These reductions were followed by marked growth releases. Even if the absence of nonhost species prevented the building of chronologies that could confirm the origin of growth reductions, the findings suggested that spruce budworm (Archips fumiferana Clemens [syn.: Choristoneura fumiferana (Clemens)]) outbreaks contribute to the formation and maintenance of the uneven-aged structure of older black spruce stands at high latitudes.