Postfire lichen–spruce woodland recovery at the limit of the boreal forest in northern Quebec

Abstract

A 250-year postfire plant chronosequence in well-drained sites at the northern limit of the Boreal Forest in the Grande rivière de la Baleine area, northern Quebec, was reconstructed from nine sites associated with the development of the lichen–spruce woodland. Most species recorded along the chronosequence reinvaded burned sites within 15 years after fire, whereas important vegetational changes occurred during the first 100 years of postfire recovery, corresponding to full development of the Cladina stellaris – spruce woodland. No vascular plant species replacement was observed during succession, whereas by contrast a well-defined lichen–bryophyte sequence occurred along five successional stages. Species diversity (Shannon index) was low 4 years after fire, but it has reached a maximum about 25 years after fire and then dropped and stabilized at a low value in old-growth woodlands dominated by black spruce (Picea mariana (Mill.) BSP) and C. stellaris. The active period of black spruce sexual regeneration spans about 20–25 years, with maximum regeneration occurring between 5 and 14 years after fire. After this period, seed regeneration is mostly sporadic and sustained layering becomes fairly common at all sites. From 100 to 250 years after fire, no significant changes were observed in vegetation structure, floristic composition, species diversity, and spruce regeneration, suggesting that lichen woodlands are selfperpetuating in absence of fire. In limiting spruce regeneration at the ground surface, the lichen cover seems to be the most important factor controlling the open structure of the lichen–spruce woodland.