Two new pollen sequences from the Bruce Peninsula, southern Ontario, demonstrate the Holocene history of forests in the area. During the mid- and late Holocene, the southern portion of the peninsula supported a rich deciduous forest, dominated by Acer saccharum and Fagus grandifolia, while the northern portion was dominated by a forest with a much higher proportion of conifers. These two sites are compared numerically with a third site, on Manitoulin Island, by means of principal components analysis. Despite similar bedrock, soils, climate, and topography, the three pollen sequences show a remarkable divergence of Holocene forest history. The role of historical factors in determining forest composition may be much greater than previously appreciated. This study emphasises the need to understand the magnitude of variation between pollen sequences within uniform terrain before ascribing the differences in pollen sequences from contrasting environments (because of climate, soils or topography) to the factors causing the obvious contrast. Key words: Holocene forest history, pollen analysis, principal components analysis, Bruce Peninsula, southern Ontario.