Thinning and underplanting of conifer plantations to promote natural succession in southern Ontario's forests for restoration purposes was examined in a young red pine (Pinus resinosa Ait.) plantation. Eleven years after application of five thinning treatments, seedling diameter, height, and stem volume of planted white ash (Fraxinus americana L), red oak, (Quercus rubra L.), and white pine (Pinus strobus L.) were positively correlated with thinning intensity and size of canopy openings. Percent survival did not differ among thinning treatments. Based on growth and survival responses, field performance of white ash and white pine was superior to red oak. Recommendations for restoring conifer plantations to native forest types are provided.