Northern Great Plains River Floodplain

This ecological system is found in the floodplains of medium and large rivers of the northwestern Great Plains, ranging from the Dakotas Mixedgrass Prairie west through the Northern Great Plains Steppe and north into Canada. This system occurs in the upper Missouri River Basin and includes parts of the Niobrara, White, Cheyenne, Little Missouri, Yellowstone, Powder, Bighorn, Milk, and Musselshell rivers. Alluvial soils and periodic, intermediate flooding (every 5-25 years) typify this system. These are the perennial big rivers of the region with hydrologic dynamics largely driven by snowmelt in the mountains, rather than local precipitation events. Dominant communities within this system range from floodplain forests to wet meadows to gravel/sand flats, however, they are linked by underlying soils and flooding regime. Dominant species are Populus balsamifera ssp. trichocarpa or Populus deltoides and Salix spp. Fraxinus pennsylvanica, Salix amygdaloides, and Ulmus americana are common in some stands. If present, common shrub species include Amorpha fruticosa, Cornus drummondii, Cornus sericea, Symphoricarpos occidentalis, Salix exigua, Salix interior, and Salix planifolia. Grass cover underneath the trees is an important part of this system and is a mix of cool-season graminoid species, including Carex pellita, Elymus lanceolatus, Pascopyrum smithii, and Schoenoplectus spp., with warm-season species such as Panicum virgatum, Schizachyrium scoparium, and Spartina pectinata. This system is often subjected to heavy grazing and/or agriculture and can be heavily degraded. In Montana, most occurrences are now degraded to the point where the cottonwood overstory is the only remaining natural component; undergrowth is dominated by Bromus inermis, or a complex of pasture grasses. Another factor is that groundwater depletion and lack of fire have created additional species changes. In most cases, the majority of the wet meadow and prairie communities may be extremely degraded or extirpated from the system.

Dominant species are Populus balsamifera ssp. trichocarpa or Populus deltoides and Salix spp. Fraxinus pennsylvanica, Salix amygdaloides, and Ulmus americana are common in some stands. If present, common shrub species include Amorpha fruticosa, Cornus drummondii, Cornus sericea, Symphoricarpos occidentalis, Salix exigua, Salix interior, and Salix planifolia. Grass cover underneath the trees is an important part of this system and is a mix of cool-season graminoid species, including Carex pellita (= Carex lanuginosa), Elymus lanceolatus, Pascopyrum smithii, and Schoenoplectus spp., with warm-season species such as Panicum virgatum, Schizachyrium scoparium, and Spartina pectinata.

This ecological system is found in the floodplains of medium and large rivers of the northwestern Great Plains, ranging from the Dakotas Mixedgrass Prairie west through the Northern Great Plains Steppe and north into Canada. Alluvial soils and periodic, intermediate flooding (every 5-25 years) typify this system. These are the perennial big rivers of the region with hydrologic dynamics largely driven by snowmelt in the mountains, rather than local precipitation events. Dominant communities within this system range from floodplain forests to wet meadows to gravel/sand flats, however, they are linked by underlying soils and flooding regime.

This system is often subjected to heavy grazing and/or agriculture and can be heavily degraded. In Montana, most occurrences are now degraded to the point where the cottonwood overstory is the only remaining natural component; undergrowth is dominated by Bromus inermis, or a complex of pasture grasses. Another factor is that groundwater depletion and lack of fire have created additional species changes. In most cases, the majority of the wet meadow and prairie communities may be extremely degraded or extirpated from the system.

This system is found in the northwestern Great Plains, north of the North Platte River through southern Canada. It is found in eastern Montana along the upper Missouri, Yellowstone, Bighorn, Milk, and Musselshell rivers; in northern Nebraska and the Dakotas on the Niobrara, upper Missouri, White, Cheyenne, and Little Missouri rivers; and in Canada on the Saskatchewan River.