Effects of fire severity and initial tree composition on stand structural development in the coniferous boreal forest of northwestern Québec, Canada

Abstract

:The effects of fire severity and initial post-fire tree composition on long-term stand structural development were investigated in the Picea mariana–feathermoss bioclimatic domain of northwestern Québec. Paleoecological methods were used to categorize the severity of the last fire (high or low) and initial tree composition (Picea mariana versus Pinus banksiana). Changes in stand structure were evaluated by quantifying stand structural attributes along three chronosequences. Except for accelerating stand break-up, the post-fire presence of P. banksiana (which is eventually replaced by P. mariana) had little effect on stand structural development. Fire severity had significant effects on the evolution of stand structural attributes, with low severity fires being particularly detrimental for stand productivity. Stands colonizing low severity fires were characterized by low post-fire tree recruitment and growth and remained open throughout succession. In contrast, after high severity fires, dense productive stands were rapidly established regardless of tree composition and gradually became open as succession proceeded. These results suggest that in the prolonged absence of fire, the different stand structural development pathways gradually converge regardless of fire severity or initial composition. We argue that stand structural diversity within the coniferous boreal forest is a result of the severity of the last fire and of processes operating at the stand scale in the absence of fire.