Lowland - Montane Riparian Deciduous Forest
Global Name
Central Rocky Mountain Lowland & Foothill Riparian Forest
No photos are currently available
Global Rank : G3? State Rank : S3S4
General Description
In Montana, this group occurs on both sides of the Continental Divide from valley bottoms into the foothills and montane zones along rivers and streams, lake margins and other wet sites. It is more common west of the Divide; east of the Divide it is more localized and scattered along low elevation streams and rivers into the montane zone in the island ranges of central Montana. It encompasses riparian forest and woodland communities dominated by Black Cottonwood (Populus balsamifera ssp. trichocarpa) or Balsam Poplar (Populus balsamifera ssp. balsamifera). These two taxa are practically indistinguishable and are often treated as a single species. In many stands, Quaking Aspen (Populus tremuloides) may be present or co-dominate. Conifer species such as Ponderosa Pine (Pinus ponderosa), Douglas-fir (Pseudotsuga menziesii) or Engelmann Spruce may be present. The undergrowth may be dominated by various shrubs or herbaceous species. Black Cottonwood communities often occur in a mosaic with willow-dominated riparian habitats.
Diagnostic Characteristics
Riparian & Wetland Forest; Rocky Mountain Region; Valleys, Foothills and Montane Zones; Floodplains; Deciduous Trees
Similar Systems
Range
In Montana, this group is found primarily west of the Continental Divide from the major river drainages to montane streams. East of the Divide, it is more localized and scattered along low elevation streams and rivers into the montane zone of the island ranges of central Montana.
Spatial Pattern
Small Patch
Environment
These riparian communities occur at lower elevations in valleys and in the foothills and montane zones on alluvial terraces, streambanks, and floodplains along low to gradient streams and rivers. Soils are usually Entisols overlying river cobbles and gravel. Inceptisols and Mollisols can be found on older sites of relative stability that have had significant time for soil development. Soil texture varies from loam to coarse sand. Water tables may drop in late summer to 50 centimeters (20 inches) below the soil surface, but surface horizons remain moist due to capillary action. The coarse textured soils, stream gradients, and large amounts of coarse rock fragments create rapid movement of highly aerated water. Sites occur at elevations of 2,500-4,000 feet west of the Continental Divide. East of the Continental Divide, this system ranges up to 5,500 feet (Hansen et al. 1995). This system is dependent on a natural hydrologic regime, especially annual or episodic flooding. Occurrences are found within the flood zone of major rivers and the associated islands, sand or cobble bars, and along adjacent streambanks. It can occur as a large, wide patch on mid-channel islands in larger rivers or as narrow bands along small, montane streams and on well-drained benches. It is also found along backwater channels and other perennially wet but less scoured sites, such as floodplains, swales and irrigation ditches.
Vegetation
This group encompasses riparian forest and woodland communities dominated by Black Cottonwood (Populus trichocarpa or Populus balsamifera ssp. trichocarpa) or Balsam Poplar (Populus balsamifera ssp. balsamifera). These two taxa are practically indistinguishable and are often treated as a single species. In many stands, Quaking Aspen (Populus tremuloides) may be present or co-dominate. Conifer species such as Ponderosa Pine (Pinus ponderosa), Douglas-fir (Pseudotsuga menziesii) or Engelmann Spruce may be present, especially in older stands or on more stable floodplains. The undergrowth may be dominated by various shrubs or herbaceous species. Common shrubs include Woods’ Rose (Rosa woodsii), Western Snowberry (Symphoricarpos occidentalis), Common Snowberry (Symphoricarpos albus), Red-osier Dogwood (Cornus sericea), Currants and Gooseberries (Ribes spp), Serviceberry (Amelanchier alnifolia), Chokecherry (Prunus virginiana) and willows (Salix spp). Common graminoids are mainly non-native species and include Kentucky Bluegrass (Poa pratensis) Canada Bluegrass (Poa compressa), Common Timothy (Phleum pratense, Redtop (Agrostis stolonifera) (Hansen etal 1995). The forb component ranges from very sparse to moderately dense or patchy with a diversity of potential native and non-native species within these habitats. Individual associations should be referenced for common forbs in each type.
Dynamic Processes
Flooding is crucial for the establishment and maintenance of Cottonwood stands within floodplain environments and acts as primary control on plant succession. High flow events lead to scouring and deposition of gravels and sediments where Cottonwoods can establish. Sediment accumulating in these systems often creates gravel bars at or near the surface of the river, creating bands of mixed vegetation occupying different stages of succession. Increasing vegetation traps even more sediment, so that over time the size and height of the gravel bar increases. Cottonwoods and the associated shrub understory are adapted to these flooding events.
Management
Alteration of hydrology by dams and diversions are major influences on the structure, composition, and function of cottonwood communities. In Montana, dams have eliminated the ability of cottonwood to regenerate by seeds in many places. As the cottonwood stand dies, successional processes will tend toward other communities unless flooding deposits new sediments that support seedling regeneration. Heavy grazing by cattle, or in some cases by elk and deer, along these streams and rivers can result in increased erosion and eliminate the vegetative regeneration of cottonwood sprouts. In sites where there is prolonged disturbance, shrub cover will decrease, resulting in a more open canopy.
Restoration Considerations
Maintaining an undisturbed buffer strip of cottonwood species adjacent to rivers and streams can stabilize riverbanks and will serve as a source for seedling and branch colonization if the hydrology of the river system is restored. Cottonwood requires full sunlight and a moist seed bed for colonization. If the site still has a fairly high water table and a remnant shrub population, the shrubs are capable of resprouting and will stabilize embankments and reduce sedimentation. If the site is highly impacted, seedlings or live cuttings can be used for more intensive restoration practices.
Original Concept Authors
G. Kittel (2015)
Montana Version Authors
S. Mincemoyer, L. Vance, C. McIntyre, T. Luna
Version Date
12/6/2024
