Oak-savanna is a wooded community with oak (Quercus spp.) canopy cover between 10 and 50% and a rich herbaceous groundcover. Oak-savanna ecosystems have been an integral part of the biodiversity in the Midwestern North America, supporting highly diverse flora and fauna. It has been estimated that oak-savannas once have covered 11-13 million hectares prior to European settlement. However, during the 19th and 20th Centuries, over 99.8% of its coverage disappeared by human activities such as conversion to agricultural lands and suppression of fires. In addition, the remnant oak-savannas have faced significant modifications in their community structures and functions. For example, fire suppression has converted once open-canopy savannas to closed-canopy forests, changing their light regimes, species compositions and vegetation dynamics. Moreover, further environmental changes that are caused by human activities, such as climate change and atmospheric deposition of nitrogen, add uncertainty to the future of the Midwestern oak-savannas. In the recent decades, there have been rising public recognitions and awareness of the oak-savanna for its values of natural heritage, biological diversity, and ecosystem services. Along with such recognitions and awareness, a majority of the research projects on the savannas have focused on structural and functional traits, role of prescribed fires, secondary succession on prior-converted old-fields, and restoration strategies. The proposed session is to explore the past changes and the current status of oak-savanna. In doing so, results from some selected projects will be presented with the topics of nature, historical changes, functional traits, functional diversity, species richness, role of fire, effects of atmospheric nitrogen deposition, and vegetation dynamics of (or in) oak-savanna. Also, the proposed session will attempt to make “best-guess” projections for changes in the future as a result of climate change.