Vegetative Community. Vegetation typically found on these sites is an overstory of green ash, pecan, Shumard oak, pin oak, bur oak, elm, and black willow with an understory of broadleaf uniola, sedges, and wild rye. When disturbed, these areas convert to black willow and green ash with an understory of sedges and annual grasses such as green spangletop. Curly dock and cocklebur are common in abandoned cropland areas.