Intensive agricultural practices across the midwestern United States cleared nearly all of the original broadleaf deciduous forest, and today restrict the selection of protected areas to regrowth stands across human-dominated landscapes. This study focused on the: (1) physical-site conditions and past land use influence woody plant diversity and the canopy structure of protected regrowth forests, and (2) relationships between these measures of structural diversity and community resistance to an invasive non-native shrub. We measured woody vegetation at 30 points in the 268 ha Bachelor Reserve, Southwest Ohio, and examined statistical relationships between physical-site conditions, historical land use since 1938, and the structural diversity of woody plants. Stand age, with topographic and soil attributes, provide unique and significant contributions to multiple regression models, explaining canopy species richness and height variability. Certain physical settings were managed in certain ways and released at similar times, confounding the interpretation of unique management effects. A diverse canopy structure shows a negative relationship with abundances of non-native Lonicera maackii (Rupr.) Herder, but the shrub is positively related with understory species richness and physical-site conditions that explain diversity in the understory. The study documents positive trends over time toward the development of regrowth broadleaf deciduous forests in the reserve, following a history of cultivation and grazing, and highlights the importance of environmental heterogeneity and size in protecting diversity across intensively managed landscapes.