Maintaining the coexistence of multiple tree species is one of the greatest issues of uneven-aged silviculture. In many places, while forest managers have successfully maintained complex stand structure with continuous cover silviculture, they have often faced difficulties to maintain some desired species mixtures. The composition of uneven-aged forests naturally evolves as few species successfully regenerate and suppress the others. Maintaining the coexistence of various tree species is however of great interests, for example, regarding biodiversity issues or resilience to global changes. Since uneven-aged silviculture usually maintains a continuous canopy cover, wherever nutrient and water availability satisfies regeneration requirements, the availability of light in the understory is the driving factor of natural regeneration dynamics. The amount of transmitted radiation determines, at least partly, regeneration composition because of interspecific differences in growth and survival under shade. In theory, shade-tolerant species generally dominate the regeneration under closed canopies whereas less shade-tolerant species dominate the regeneration under partially open canopies. We hypothesized that, along a gradient of light availability, there is a rank reversal of sapling growth of species with contrasting shade-tolerance. In addition, we expected that forest managers can effectively control understory light with appropriate modifications of forest structure and density. We examined mixtures of sessile oak (Quercus petraea (Matt.) Liebl.) and European beech (Fagus sylvatica L.) in the Belgian Ardennes. We selected 23 sites with favorable water and nutrient supply. Regeneration areas (100-6500m²) were fenced off to protect them from browsing by deer. Saplings were sampled in 241 subplots and their height growth was annually monitored during two years. Understory light transmittance was measured in each subplot using hemispherical photography. The height growth of beech and oak saplings was modeled with mixed non-linear models. In order to simulate various silvicultural treatments, we used a model of light interception by heterogeneous canopies (SAMSARALIGHT). We simulated selective thinnings of 5 different types: harvesting preferentially small trees, large trees, or trees of shade-tolerant species or creating circular gaps. Understory light was found to be a key parameter in the dynamics of heterogeneous stands, as it affects regeneration growth and composition. There were interspecific differences in growth response to light availability. The optimum height growth of beech and oak regenerations were reached at 10% and 20% of transmittance, respectively. Our simulations highlighted that various silvicultural treatments can effectively be used to control understory light as long as harvest intensity is adapted to the chosen strategy. The results of this study also underscore the problem that even under good light conditions (transmittance > 20 %), regeneration of less shade-tolerant species might not overcome the regeneration of shade-tolerant species. Contrary to our hypothesis, we found no rank reversal of the height growth of the two study species along a wide light gradient. Consequently, maintaining less shade-tolerant species in stands with shade-tolerant species might require silvicultural interventions jointly in the overstory and regeneration layers.