ECOLOGICAL ANALYSIS OF BLACK ASH STANDS (FRAXINUS-NIGRA) ON THE SHORE OF LAKE DUPARQUET (NORTHWESTERN QUEBEC)

Spring and early summer flood is one of the main factors affecting the dynamics of black ash (Fraxinus nigra Marsh.) stands growing on lake floodplains in the boreal forest. The effect of flooding on the vegetation was studied in five stands on the shore of Lake Duparquet in Abitibi, northwestern Quebec. Divisive hierarchical classification analysis (Twinspan) revealed the existence of four different vegetation types: (i) black ash - speckled alder (Alnus rugosa) - bog willow (Salix pedicellaris), (ii) black ash - balsam poplar (Populus balsamifera) - ostrich fern (Matteuccia struthiopteris), (iii) black ash - pussy willow (Salix discolor) - sensitive fern (Onoclea sensibilis), and (iv) black ash - speckled alder - sensitive fern. Detrended correspondance analysis (Decorana) shows that elevation and drainage are the main factors affecting plant distribution and dynamics. Geomorphology also plays a major role in the way each stand responds to flooding. For each of the vegetation types studied, black ash shows a particular regeneration pattern and sexual regeneration tends to become less frequent with increasing exposure to flooding. Finally, the strong sexual regeneration and the youth of the populations found in the most elevated sites could be related to a possible alteration of the flood regime.