Small Mammal Populations on the Islands of Basswood Lake, Minnesota

Abstract

Islands have long been recognized as having faunas with unique properties. Beginning in 1950 the Quetico-Superior Wilderness Research Center, by giving support and making available its facilities, made it possible for us to conduct investigations on the small mammals found on the islands in Basswood Lake, Lake County, Minnesota. This paper reports on three years' work in which we have attempted to ascertain the status of the natural populations on these islands. The study was set up to determine (1) whether or not the islands of Basswood Lake would show relatively complete isolation throughout the year with water in the summer and ice in the winter serving as effective barriers to ingress and egress and (2) to determine some of the characteristics of the small mammal populations on these islands. Basswood Lake is typical of the large lakes along the Ontario-Minnesota boundary. These lakes lie in rock-bound basins formed by the glaciers of the Pleistocene Epoch (Zumberge 1952). The upland is characterized by numerous low bedrock hills and knobs which are covered with a very thin mantle of glacial drift (Thiel 1947). Interspersed among these hills are numerous swamps and small lakes. The original dominant vegetation of this area was composed primarily of conifers. The characteristic trees of the upland forest were the red and white pines, white spruce, balsam fir and white birch while the swamps were filled with black spruce, tamarack, white cedar and black ash. Deciduous trees such as aspen, balsam poplar, red maple, pin cherry, yellow birch and mountain ash were found throughout the area, but except where there had been some disturbance, they formed only a small part of the vegetation (Rosendahl and Butters 1928). The present vegetation shows the effects of heavy logging, burning and reburning. The destruction of the original forest was followed by the rapid growth of aspen and white birch which, at the present time, form the dominant part of the flora. The islands, for the most part, were affected less by these destructive forces than the mainland.