Quantitative data on structure and composition of all strata of vegetation were collected from 20 study sites in the Boston Mountains Subsection of the Ozark Mountains of northwestern Arkansas in June 2004. All study sites were located at upper slope or ridgetop positions and occurred at elevations > 457 m. Oaks (Quercus spp.) were dominants in the tree stratum (stems ≥ 10 cm DBH) for all 11 sites located < 549 m but in only one site > 590 m. In these higher elevation sites, various other species, including sugar maple (Acer saccharum), were relatively more important. Hickories (Carya spp.) were consistently present but usually achieved dominant or codominant status only at higher elevations. Dogwood (Cornus florida) and red maple (A. rubrum) were the two most important species represented in the small tree (stems ≥ 2.5 cm but < 10 cm DBH) stratum.