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Forest: Forests occupied river terraces and large and small islands within the floodplain <br />that have sufficient substrate over groundwater to allow root development and aeration <br />(floodplain forests). Forests were also found in draws, fields, and drainages outside the <br />floodplain (upland forests). Forests were found along all transects except for two, <br />Transects 25 and 26 at Jeffrey Island. The mean density of all trees (11 species) at Jeffrey <br />Island was 68 per ha, and the mean density of all shrubs /saplings (20 species) in the <br />understory was 241 per ha. The mean density of all trees (11 species) at Cottonwood <br />Ranch was 133 per ha, and the mean density of all shrub /saplings (13 species) in the <br />understory was 1,635 per ha. <br />Cottonwood (Populus deltoides) was the most common tree on both properties; the <br />average density at Jeffrey Island was 35 trees per ha and the average density at <br />Cottonwood Ranch was 43 trees per ha. In general, the cottonwoods were more mature <br />at Cottonwood Ranch than at Jeffrey Island, as evidenced by an average diameter of all <br />cottonwoods at Cottonwood Ranch of 46 cm compared to 36 cm at Jeffrey Island. Other <br />common species on both properties included green ash (Fraxinus pennsylvanica), <br />American elm (Ulmus americana), Eastern red cedar (Juniperus virginiana), and white <br />mulberry (Morus alba). The species composition of the understory included a mix of <br />young trees less than 5 cm diameter (saplings) and shrubs, with slightly more tree species <br />than shrub species. However, the species with the greatest mean density at both <br />properties was a shrub, rough- leaved dogwood (Cornus drummondii). The mean density <br />of rough- leaved dogwood was 64 stems per ha at Jeffrey Island, followed by false indigo <br />(Amorpha fruticosa) (52 stems per ha) and prairie wild rose (Rosa arkansana) (21 stems <br />per ha). The mean density of rough - leaved dogwood at Cottonwood Ranch was 1,010 <br />stems per ha, followed by American elm (431 stems per ha) and Eastern red cedar (131 <br />stems per ha). The sapling data indicate a successional trend toward a green <br />ash/American elm community. River -bank grape (Vitus riparia) was a common woody <br />vine in the forest understory, along with poison -ivy, a sub - shrub. The percent plant cover <br />of the herbaceous understory in the forests was 71 percent at Jeffrey Island and 79 <br />percent at Cottonwood Ranch. Grasses such as downy brome, Kentucky bluegrass (Poa <br />pratensis), Canada wild rye (Elymus canadensis), dichanthelium (Dichanthelium <br />oligasanthes), prairie cordgrass (Spartina pectinata), and sand dropseed were the most <br />common herbaceous understory speices. Other common species included common <br />ragweed, black medick (Medicago lupulina), Virginia creeper (Parthenocissus <br />quinquefolia), white avens (Geum candensis), and seedlings of rough - leaved dogwood. <br />Grassland: Grasslands occurred both on drier, elevated soils that are not subirrigated and <br />on subirrigated soils within the floodplain. Grasslands were found along all transects <br />except for three, Transects 34 and 35 at Jeffrey Island and Transect 36 at Cottonwood <br />Ranch. The percent plant cover on the grasslands was 95 percent at Jeffrey Island and 93 <br />percent at Cottonwood Ranch. This cover type was dominated by a mix of native and <br />non - native grasses and forbs. Common native grasses included windmill grass (Chloris <br />verticillata), switchgrass (Panicum virgatum), prairie cordgrass, sand dropseed, little <br />barley (Hordeum pusillum), foxtail barley (Hordeum jubatum), and Kentucky bluegrass <br />(this species is considered both native and introduced); common non - native grasses <br />included downy brome, quackgrass (Agropyron repens), tall wheatgrass (Agropyron <br />