A COMMUNITY OF ARCTIC–ALPINE PLANTS ON THE EAST SHORE OF LAKE SUPERIOR

Abstract

This paper reports the discovery of a community of arctic–alpine plants on the cliffs, rocky ledges, and boulder beaches along the south shore of Old Woman Bay. The site is located on the east shore of Lake Superior at approximately 47° 47′ N. lat., 84° 54′ W. long., in the District of Algoma, Ontario. Reference is made to earlier reports of arctic–alpine plants occurring in the Lake Superior region and to important collections from the north and east shores of the lake already available in herbaria. A description is given of the site at Old Woman Bay and of the plant community discovered there, together with a presence list of 40 species of vascular plants. Collections made at the site are cited in an annotated list and distribution maps with special comments are provided for the following species: Woodsia alpina, Trisetum spicatum var. pilosiglume, Polygonum viviparum, Sagina nodosa, and Saxifraga aizoön var. neogaea. A list of bryophytes is also included.It is suggested that the arctic–alpine species reached the Old Woman Bay region by a natural migration during or soon after the retreat of the last glaciers of the Wisconsin stage of the Pleistocene ice age. Later the boreal forest invaded the area but the arctic–alpine species have been able to survive on the rocky shores where suitable habitats with cooler microclimatic conditions prevail. This explanation entails assuming an age for the community in the order of at least several thousand years. The possibility of recent introductions of these species is considered improbable.