Background: In the eastern US, upland oak forests maintain dominance through adaptations that facilitate their persistence in fire-prone environments while simultaneously contributing to a feedback loop that promotes fire. This loop can create a seemingly stable steady state where oak forests self-replace following fire disturbances; however, abrupt alterations to the natural fire regime via anthropogenic fire exclusion may cause a rapid transition to an alternative state by allowing tree species that are fire-intolerant and shade-tolerant to outcompete oaks in the absence of fire. This new state is hypothesized to be driven by a mesophication process, which is a positive feedback loop between (1) anthropogenic fire exclusion, (2) the spread of fire-sensitive, shade-tolerant tree species (i.e., mesophytes) that create cool, moist conditions in the forest understory through their canopy, bark, and litter traits, and (3) a subsequent reduction in flammability. Thus, in the absence of fire disturbances, mesophytes may foster their own proliferation through a variety of mechanisms, while increasing vulnerability and decreasing resilience of upland oak forests. Goals: (1) Bring together researchers at the forefront of this topic to explore the various mechanisms of mesophication, and (2) Gain a more holistic understanding of the vulnerability and resilience of current oak forests and the consequences of mesophication and compositional changes for future forest function. Objectives: (1) Provide a forum for presenting a wide range of case studies assessing causes, mechanisms, and consequences of mesophication in eastern oak forests, and (2) Showcase studies investigating mesophication across multiple ecological levels, from population, community, ecosystem, and landscape scales. Importance and Interest: Mesophication is commonly cited as a major cause of changing forest dominance, yet scant empirical evidence exists regarding the mechanisms of mesophication and consequences for future forest function. Upland oak forests provide a wealth of ecological and economic services including hard mast production, wildlife habitat, timber, and water resources. As such, there is a critical need to understand key ecological mechanisms that control the mesophication feedback loop, which can only be achieved by (1) delineating the fundamental mechanisms that allow mesophytes to alter their growing environment in ways which diminish forest flammability, and (2) quantifying the spatial and temporal extent over which this occurs. A mechanistic understanding of mesophication will enable more refined predictions of the equilibrium change and thresholds for these ecosystems, and in turn, their future functioning.