In 1938, four permanent 0.04-ha (0.1-acre) plots were established in pioneer aspen (Populus grandidentata Michx. and P. tremuloides Michx. forests on dry-mesic to wet-mesic soils in Michigan. These sites are representative of the soils and vegetation types found in the region. Patterns of survival, growth, recruitment of individual woody stems are determined from remeasurements in 1945, 1951, 1955, 1968, 1973, and 1979. Five patterns of change in species populations are identified, reflecting differences in reproductive characteristics and physiological requirements of the species: (1) early dominance, (2) delayed dominance, (3) persistence, (4) progressive recruitment, and (5) late recruitment. Patterns 1, 3, and 4 predominated on dry-mesic soils, reflecting slow replacement of aspen by Pinus resinosa Ait. and P. strobus L. from seedling origin, whereas all five patterns occurred on the mesic soils where Acer rubrum L., A. saccharum Marsh., and Fagus grandifolia Ehrh. increased in importance through both vegetative sprouting and seedling establishment. Recruitment on the dry-mesic soils did not correspond to the stages of development of the aspen overstory as determined from -3/2 thinning curves. In contrast, recruitment and growth in the understory appeared to be dependent upon the occurrence of canopy openings on the mesic soil. Species populations responded to insect defoliation on the wet-mesic plot, illustrating the importance of understanding population dynamics in studies of succession.