The presettlement upland boreal forest type of Isle Royale National Park, as reconstructed from the original land survey notes of 1847-48, was compared with the existing forest as sampled in 1974. A drastic reduction in balsam fir and an increase in white birch and aspen have occurred. These changes are attributed to the high frequency of man-caused fires since 1848. A reduction in tamarack is probably the result of an invasion of the larch sawfly. Thimbleberry has replaced American yew as the prevailing understory shrub. Proliferation of thimbleberry probably followed fires in the late 1800's and the failure of American yew to replace it is the result of heavy moose browsing on this highly palatable species. Forest Sci. 24:115-121.