Much of the biodiversity in a forest comes from the understory vegetation. However, centuries of fire suppression in the western United States have made human-implemented disturbance necessary for reinstating natural disturbance cycles. However, the mechanical thinning and prescribed burning treatments used by land managers may differentially affect the response of the understory community. This study aimed to compare how prescribed fire and mechanical thinning treatments, with the size and severity of those treatments, affect understory plant communities in aspen-conifer forests over time. We sampled the understory community in burned, mechanically thinned, and untreated forest stands one, three, or five years post-treatment. Within these treatment areas, we measured understory cover, species richness, and leaf area index in belt transects, and we calculated species diversity and non-native cover for each transect. Understory cover increased in burn and mechanical treatments over time and was significantly higher in burned treatments than in untreated stands five years after treatments. Additionally, understory cover was highest in large, low-severity fires. Species richness also increased in burned areas as time since treatment increased. Species richness and species diversity positively correlated with canopy openness in untreated plots, while the cover of non-native species positively correlated with fire severity. Large, lower-severity burns had the most significant positive impact on understory plant communities, but these impacts may take time to become apparent.