Structure and dynamics of conifer–lichen stands on rock outcrops south of Lake Abitibi, Quebec

Abstract

The plant communities of shallow soil and bare rock on outcrops of rhyolite and basalt are described for the area south of Lake Abitibi, Quebec. Analysis of data from 34 sample plots by means of reciprocal averaging ordination indicates that most of the intersite variation in composition and structure is due to succession. The two rock types have distinctive assemblages of epilithic lichens and bryophytes but their thin soil communities do not differ significantly. Soil coverage and depth are controlled in part by bedrock slope and microtopography and increase uniformly in relation to the postfire age of the outcrop tree stands. The ground layer macrolichens and bryophytes undergo a succession of dominant species and growth forms, but the open-crown coniferous stands show little evidence of self-regeneration through tree seedling establishment or vegetative propagation. Stands of different age dominated by Pinus banksiana and by Picea mariana do not form a clear successional sequence. Fire recurrence prevents complete closure of the outcrop tree canopy.