The recruitment of forest trees depends on survival and growth during the developmental stages prior to reaching canopy status. During growth towards the canopy, the amount of light received by young saplings is critical to success or failure. Variation in the architecture of the canopy and subcanopy produces extensive patchiness in the amount of light reaching the understory. The responses of young trees to this patchiness depend on their tolerance of shade and on the specific nature of the patchiness. A study of the responses of Acer saccharum (Marsh.) and Acer rubrum (L.) saplings to patchiness of light regimes was carried out in a stand of mature Populus grandidentata (Michx.) and Populus tremuloides (Michx.). Located on the property of the UMBS near Pellston in northern lower Michigan, this stand is currently undergoing a transition from early pioneer species to species indigenous to the Northern Hardwood-Hemlock-White Pine forest. The effects of heterogeneity in available light on distribution and abundance, growth, and mortality were studied. In addition, the canopy characteristics responsible for this heterogeneity were investigated. The results indicate that patterns of response can be explained by differences in shade tolerance and patchiness among light regimes. Due to differences in the architecture and leaf attributes of the species comprising the subcanopy and canopy, the canopy was found to have a lesser impact on light regimes than the subcanopy. Comparisons of the two species revealed that Acer rubrum was much more sensitive to microenvironments with low light conditions than Acer saccharum. In addition, this sensitivity appeared to occur at a very small size in Acer rubrum.