Stands studied in 1934 by Potzger (1941) were restudied in 1974 revealing changes in the composition of the Mackinac Island, Michigan, boreal-conifer-hardwood forest. Hardwood stands on the higher center of the island were dominated by Acer saccharum, Quercus borealis maxima, Abies balsamea, Betula papyrifera and Fagus grandifolia in order of basal area. By 1974, Fagus had become second in basal area and first in importance value. Hardwood tree stands increased in basal area from 33.85 to 42.57 m2/ha for an average annual increase of 0.22 m2/ha, while the number of trees in the 2500 m2 sample remained almost the same. A boreal conifer forest occupies the lower island periphery, dominated in both years by Thuja occidentalis, unlike surrounding mainland areas where Picea glauca and Abies balsamea are the dominants. The main change was the increase in dominance of Pinus strobus from fifth to second and the decline in dominance of Picea glauca and Abies balsamea. Also conifer stands are being invaded by Acer saccharum. Conifer stand basal area increased from 48.24 to 53.60 m2/ha, with a reduction in number of trees of 833 to 522 in the 2500 m2 sample.