Understanding structural characteristics that are responsible for biomass recalcitrance by identifying why it is more difficult for some plants, or portions of plants, to release their sugars would be extremely valuable in overcoming this barrier. With this in mind, this study investigated the recalcitrance of wood by considering the effects of aging in two Populus tremuloides cross sections. By applying our novel small scale systems, including a multi-well pretreatment and enzymatic hydrolysis system and a downscaled compositional analysis procedure, we were able to follow ring-by-ring compositions and sugar release patterns. Observed variations were then related to structural changes that occur across the radial direction of trees, providing an important step toward understanding the influence of these changes on recalcitrance. (C) 2010 Elsevier Ltd. All rights reserved.