THREATENED DRY GRASSLANDS IN THE CONTINENTAL BOREAL FORESTS OF WOOD BUFFALO NATIONAL-PARK

Dry grasslands in Wood Buffalo National Park are unique biological fea tures at 60 degrees N latitude, since they contain plant species norma lly found in more southern grasslands at 50-55 degrees N latitude. The objectives of this study were to inventory dry grasslands, classify t hem according to similarity of species cover, and establish relationsh ips with understory species in Populus tremuloides and shrub communiti es. Dry grasslands were studied at nine sites; most were clustered in the Salt River and Peace Point areas. The largest unit of grassland wa s about 3.0 ha, and most units were less than 0.5 ha. This contrasts w ith the hundreds of hectares recorded earlier in the century. Of the 1 28 vascular plant species identified, 29 are considered as southern, a nd of these, 15 are regionally rare. Sixty-four plots were classified into nine community types, using two-way indicator species analysis. A group of six communities were dominated by grass and shrub species wi th a component of southern grassland species. Three communities, stron gly dominated by Populus and shrubs, represent community types that in vade dry grasslands. Ordination of plots using detrended correspondenc e analysis showed relationships among the community types and a clear separation of southern grassland species from those found in forest co mmunities. Vascular plant diversity, as represented by mean species ri chness, ranged from about 15 to 28, and Shannon diversity indices rang ed from 1.883 to 2.615. The cover of southern grassland species was ne gatively correlated (correlation coefficient of -0.524) with cover of tall shrubs and trees, suggesting that the dry grasslands of Wood Buff alo National Park are threatened by tree and shrub invasion, which is due, in part, to a lack of recent fires at these sites.