Vegetation Development Following Fire in Picea Mariana (Black Spruce)- Pleurozium Forests of South-Eastern Labrador, Canada

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Abstract
The pattern of post-fire vegetation development in P. mariana (black Spruce)- Pleurozium forests in southeastern Labrador, Canada, is evaluated using paleoecological methods and vegetation analysis of extant stands. Macrofossil analysis of mor humus profiles in mature stands yields the following stratigraphy: mineral soil-charcoal-Polytrichum juniperinum-Cladonia lichens-Pleurozium schreberi-feather mosses and Sphagnum girgensohnii. The stratigraphic record of the post-fire dynamics of the vegetation at individual sites strengthens the conclusions obtained from the detailed analysis of chronosequence of stands. The patterns of vegetation development, especially of the arboreal species, is significantly different from the reported for the central and western boreal forest in North America. This difference is attributed to the much longer fire cycle in the maritime region of Labrador which allows the accumulation of a thick organic soil layer that is incompletely removed by fire. Arboreal regernation is slow due to the limited availability of mineral soil seedbeds. The progressive establishment of black spruce and balsam fir over a 70-100 yr period results in an uneven age structure and provides a long period when lichen woodlands cover the landscape. The majority of the vascular understorey species follow the pattern of initial floristics and resprout rapidly following fire. Coptis groenlandicum, Gaultheria hispidula, and Empetrum nigrum decrease following fire whereas only Epilobium angustifolium shows a marked increase. The cryptogam ground cover undergoes a physiognomic and compositional succession that represents contrasting substrate requirements and the differential response of the major species to a temporally-varying enviroment.