In each site (1200 m²), three circular plots (400 m²) were established (total of 198 plots). Data presented here for 1) plant of the herb layer and 2) shrub and tree are grouped by site (addition of three plots). In the herb layer, total plant species identity and abundance (percentage cover) were sampled in each plot using eight circular micro-plots of 4 m². Data were collected in 2016 and 2017, between June and August. To minimize seasonal variability and allow detection of early spring species, plants (identity and abundance) in the herb layer were measured twice (once in June to early-July, and once in late-July to August). For tree, in each plot, species identity, diameter at breast height (DBH, 1.3 m) and locations of each tree > 9.1 cm DBH were determined. In each plot, species identity and DBH of shrubs and small trees (DBH range: 1.1 to 9.1 cm) were measured in three circular micro-plots of 25 m². Data that were related to the shrub-canopy layer included all trees and shrubs with DBH > 1.1 cm. Here, in each site, forest composition and structure is represented by different combinations of DBH classes (1.1-4 cm, 4-9.1 cm, 9.1-20 cm, 20-35 cm, >35 cm) and species. Plant community composition and abundance were assessed in unmanaged forests (sites of old-growth forest > 100 years, with dominant and co-dominant trees older than 200 years, and no obvious sign of past harvesting), and in even-aged and uneven-aged managed forests along a chronosequence (< 5 years, 15 years, 30 years after forest harvesting).