The objective of this study was to quantify understory species diversity response to overstory manipulation of Blue Mountain eco-region forest. Forty nine ecological land units, including differing successional stages (sapling, pole, small saw, and saw log) and canopy cover (light and medium) in dry Grand Fir (Abies grandis), wet Grand Fir, dry Douglas Fir (Pseudotsuga menziesii), wet Douglas Fir, Ponderosa Pine (Pinus ponderosa) habitat types, and non-forest communities (Wet Meadow, Riparian Grass, Grassland, and Scabland) were sampled for production by species with 3 to 15 replicates per ecological land unit, over 3 consecutive years. The Shannon diversity index (H) was used to characterize species diversity in a community. Species diversity (H) and evenness (EH) for forest communities ranged from 1.61 to 1.96 and from 0.61 to 0.68, respectively. Wet Grand Fir habitat type had higher diversity (P < 0.01) than the other habitat types. Non-forest communities were similar (P > 0.01) in species diversity and evenness, ranging from 1.46 to 1.62 and from 0.54 to 0.67, respectively. Although dry and wet environments did not influence (P > 0.01) Douglas Fir understory diversity, wet Grand Fir habitat type tended to be more diverse. Early successional stage in forest habitats had higher (P < 0.01) species diversity and evenness (H = 1.93 and EH = 0.68) compared to later successional stages (H = 1.69 and EH = 0.63). Light and medium densities of overstory canopy cover did not influence (P > 0.01) diversity of understory vegetation. Diversity in recently logged habitats was not different (P > 0.01) from other successional stages. In summary, diversity of forest communities was influenced by overstory manipulation with greater diversity in early successional stages.