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Northern Rocky Mountain Lower Montane Riparian Woodland and Shrubland

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Provisional State Rank: S4
* (see reason below)

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State Rank Reason
This system faces multiple threats: residential and agricultural development, invasives, climate change, drought, etc. However, it is still widespread.
 

General Description

This ecological system is found throughout the Rocky Mountain and Colorado Plateau regions. In Montana, sites occur at elevations of 609-1,219 meters (2,000-4,000 feet) west of the Continental Divide. East of the Continental Divide, this system ranges up to 1,676 meters (5,500 feet). It generally comprises a mosaic of multiple communities that are tree-dominated with a diverse shrub component. It is dependent on a natural hydrologic regime with annual to episodic flooding, so it is usually found within the flood zone of rivers, on islands, sand or cobble bars, and along streambanks. It can form large, wide occurrences on mid-channel islands in larger rivers, or narrow bands on small, rocky canyon tributaries and well-drained benches. It is also typically found in backwater channels and other perennially wet but less scoured sites, such as floodplains, swales and irrigation ditches. In some locations, occurrences extend into moderately high intermountain basins where the adjacent vegetation is sage steppe. Black cottonwood (Populus balsamifera ssp. trichocarpa) is the key indicator species. Other dominant trees may include boxelder maple (Acer negundo), narrowleaf cottonwood (Populus angustifolia), eastern cottonwood (Populus deltoides), Douglas-fir (Pseudotsuga menziesii), peachleaf willow (Salix amygdaloides), or Rocky Mountain juniper (Juniperus scopulorum). Dominant shrubs include Rocky Mountain maple (Acer glabrum), thinleaf alder (Alnus incana), river birch (Betula occidentalis), redoiser dogwood (Cornus sericea), hawthorne (Crataegus species), chokecherry (Prunus virginiana), skunkbush sumac (Rhus trilobata), willows (Salix species), rose (Rosa species), silver buffaloberry (Shepherdia argentea), or snowberry (Symphoricarpos species).


Diagnostic Characteristics
Forest and Woodland, shrub dominated, lower montane to montane elevations, riverine-alluvial, short flooding interval (<5 yrs)

Similar Systems

Range
This system is found at low to mid elevation throughout the mountains and foothills of Montana.

Ecological System Distribution
Approximately 2,683 square kilometers are classified as Northern Rocky Mountain Lower Montane Riparian Woodland and Shrubland in the 2013 Montana Land Cover layers.  Grid on map is based on USGS 7.5 minute quadrangle map boundaries.



Montana Counties of Occurrence
BEAVERHEAD, BIG HORN, BLAINE, BROADWATER, CARBON, CASCADE, CHOUTEAU, DEER LODGE, FERGUS, FLATHEAD, GALLATIN, GLACIER, GOLDEN VALLEY, GRANITE, HILL, JEFFERSON, JUDITH BASIN, LAKE, LEWIS AND CLARK, LIBERTY, LINCOLN, MADISON, MEAGHER, MINERAL, MISSOULA, PARK, PONDERA, POWELL, RAVALLI, SANDERS, SILVER BOW, STILLWATER, SWEET GRASS, TETON, TOOLE, WHEATLAND

Spatial Pattern
Linear

Environment
This riparian system is a seasonally flooded shrubland and woodland found throughout the northern Rocky Mountain region. It occurs at lower montane elevations in valleys and foothills on alluvial terraces, streambanks, and floodplains along moderate to high 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 609-1,219 meters (2,000-4,000 feet) west of the Continental Divide. East of the Continental Divide, this system ranges up to 1,676 meters (5,500 feet) (Hansen et al., 1995).

Vegetation

Black cottonwood (Populus balsamifera ssp. trichocarpa) is the key indicator species. Several other tree species can be mixed in the canopy, including boxelder maple (Acer negundo), narrowleaf cottonwood (Populus angustifolia), eastern cottonwood (Populus deltoides), Douglas-fir (Pseudotsuga menziesii), peachleaf willow (Salix amygdaloides), or Mountain juniper (Juniperus scopulorum). Quaking aspen (Populus tremuloides), paper birch (Betula papyrifera), water birch (Betula occidentalis) and white spruce (Picea glauca) also occur. Grand fir (Abies grandis), western red cedar (Thuja plicata), and western hemlock (Tsuga heterophylla) are commonly co-dominant canopy species in western Montana occurrences, particularly in lower montane riparian zones. Shrub understory components include red-oiser dogwood (Cornus sericea), Rocky Mountain maple (Acer glabrum), thinleaf alder (Alnus incana), devil’s club (Oplopanax horridus), and common snowberry (Symphoricarpos albus). Other shrubs may include currant (Ribes species), Douglas hawthorn (Crataegus douglasii), plane leaf willow (Salix planifolia) yellow willow (Salix lutea), Woods’ rose (Rosa woodsii), alder buckthorn (Rhamnus alnifolia), and common chokecherry (Prunus virginiana). Shrubby cinquefoil (Dasiphora fruticosa), Drummond’s willow (Salix drummondii), and sandbar willow (Salix exigua) are often present on recent alluvial bars.

Dominant graminoid vegetation in the herbaceous stratum includes bluejoint reedgrass (Calamagrostis canadensis), and to a much lesser extent, blue wildrye (Elymus glaucus) and Bebb’s sedge (Carex bebbii). Common forbs include yarrow (Achillea millefolium), fireweed (Chamerion angustifolium), swamp willow herb (Epilobium palustre), common cowparsnip (Heracleum maximum), aster (Symphyotrichum species), western meadow rue (Thalictrum occidentale), Canada goldenrod (Solidago canadensis), starry solomon’s seal (Maianthemum stellatum), clasping-leaf twisted stalk (Streptopus amplexicaulus) and western sagewort (Artemisia ludoviciana). Fern and fern ally cover is often high and includes species such as American ladyfern (Athyrium filix-femina), oak fern (Gymnocarpium dryopteris), and horsetails (Equisetum species).

Flooding in these systems influences community composition by transporting sediments and creating establishment sites for colonization. Plants have acquired adaptive traits to survive in these high-energy flood-disturbance settings. Many plants have flexible, resilient stems and specialized cells to hold oxygen so that they can survive large flood events; some have reproductive adaptations like water-dispersed seeds and are able to sprout quickly from damaged stumps.


Alliances and Associations
Alliances
  • (A.311) Black Cottonwood Temporarily Flooded Forest Alliance
  • (A.176) Grand Fir Temporarily Flooded Forest Alliance
  • (A.267) Paper Birch Forest Alliance
  • (A.145) Western Hemlock Forest Alliance
  • (A.174) Western Hemlock Temporarily Flooded Forest Alliance
  • (A.166) Western Red-cedar Forest Alliance
  • (A.193) Western Red-cedar Seasonally Flooded Forest Alliance

Dynamic Processes
Stochastic flood events and variable fluvial conditions are crucial to the development of establishment sites for riparian plants, and exert a primary control on plant succession. In areas with steep gradients, high-energy flows precipitated by snowmelt, rain-on-snow events or convective thunderstorms lead to floods, which in turn scour and transport coarse sediments. The scouring out and downstream accumulation constantly creates and destroys sites for the establishment of vegetation. Gravel bars are created at or near the surface of the river, where vegetation colonizes. As the gravel and point bars extend, mixed vegetation bands grow up, representing different stages of succession. The vegetation traps even more sediment, so that over time the size and height of the gravel bar increases. As gravel bar height increases, backwater channels can establish. These channels hold early runoff for an extended time, and are also fed by ground water seepage. Further from the channel, groundwater recharge from snowmelt may create shallow water tables or seeps that support vegetation when stream flow is low.

Management

Grazing, timber harvest, recreation and residential development can all alter structure, composition, and function of this system. Poor grazing practices can result in increased erosion and channel downcutting, limiting the overbank flows that drive succession. Where grazing is excessive, shrub cover will decrease, resulting in a more open canopy. Continued heavy grazing can completely eliminate cottonwood regeneration, and herbaceous vegetation will eventually transition to a system dominated by grasses such as redtop (Agrostis stolonifera), fowl bluegrass (Poa palustris), Canada bluegrass (Poa compressa), Kentucky bluegrass (Poa pratensis) and other exotic perennial forbs. Any activity that alters the hydrology of these systems (e.g., improperly sized culverts, land clearing and compaction, water diversion and withdrawal, and rip-rap installation) can eventually lead to a loss of characteristic disturbance-prone vegetation communities.


Restoration Considerations
Restoration strategies are dependent on the level and type of disturbance event. Because all shrub species within this system are capable of resprouting, modified land management practices in areas of low to moderate impact can minimize additional restoration needs. Highly impacted sites and areas of potential soil erosion may require soil stabilization and, in some cases, reseeding or replanting.

Species Associated with this Ecological System
  • Details on Creation and Suggested Uses and Limitations
    How Associations Were Made
    We associated the use and habitat quality (high, medium, or low) of each of the 82 ecological systems mapped in Montana for vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
    1. Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Foresman 2001, Adams 2003, and Werner et al. 2004);
    2. Evaluating structural characteristics and distribution of each ecological system relative to the species’ range and habitat requirements;
    3. Examining the observation records for each species in the state-wide point database associated with each ecological system;
    4. Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system to get a measure of “observations versus availability of habitat”.
    Species that breed in Montana were only evaluated for breeding habitat use, species that only overwinter in Montana were only evaluated for overwintering habitat use, and species that only migrate through Montana were only evaluated for migratory habitat use.  In general, species were associated as using an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.  However, species were not associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system, even if point observations were associated with that system.  High, medium, and low habitat quality was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species in the literature.  The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignments of habitat quality.  If you have any questions or comments on species associations with ecological systems, please contact Bryce Maxell at bmaxell@mt.gov or (406) 444-3655.

    Suggested Uses and Limitations
    Species associations with ecological systems should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning.  These potential lists of species should not be used in place of documented occurrences of species (this information can be requested at: http://mtnhp.org/requests/default.asp) or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.  Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.  Land cover mapping accuracy is particularly problematic when the systems occur as small patches or where the land cover types have been altered over the past decade.  Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections).  Finally, although a species may be associated with a particular ecological system within its known geographic range, portions of that ecological system may occur outside of the species’ known geographic range.

    Literature Cited
    • Adams, R.A.  2003.  Bats of the Rocky Mountain West; natural history, ecology, and conservation.  Boulder, CO: University Press of Colorado.  289 p.
    • Dobkin, D. S.  1992.  Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34.  Missoula, MT.
    • Foresman, K.R.  2001.  The wild mammals of Montana.  Special Publication No. 12.  Lawrence, KS: The American Society of Mammalogists.  278 p.
    • Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998.  Montana atlas of terrestrial vertebrates.  Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT.  1302 p.
    • Hutto, R.L. and J.S. Young.  1999.  Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32.  72 p.
    • Maxell, B.A.  2000.  Management of Montana’s amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species.  Report to U.S. Forest Service Region 1.  Missoula, MT: Wildlife Biology Program, University of Montana.  161 p.
    • Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath.  2004.  Amphibians and reptiles of Montana.  Missoula, MT: Mountain Press Publishing Company. 262 p.

Original Concept Authors
Natureserve Western Ecology Group

Montana Version Authors
L.K. Vance, C. McIntyre, T. Luna

Version Date
1/22/2010

References
  • Classification and Map Identifiers

    Cowardian Wetland Classification: Not applicable

    National Vegetation Classification Standard: Not applicable
    NatureServe Identifiers:
    Element Global ID 28640
    System Code CES306.804, Northern Rocky Mountain Lower Montane Riparian Woodland and Shrubland

    ReGAP:
    9155: Northern Rocky Mountain Lower Montane Riparian Woodland and Shrubland


  • Additional ReferencesLegend:   View WorldCat Record   View Online Publication
    Do you know of a citation we're missing?
    • Hansen, P. L., R. D. Pfister, K. Boggs, B. J. Cook, J. Joy, and D. K. Hinckley. 1995. Classification and management of Montana's riparian and wetland sites. Montana Forest and Conservation Experiment Station, School of Forestry, University of Montana, Miscellaneous Publication No. 54. 646 pp. + posters.

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Citation for data on this website:
Northern Rocky Mountain Lower Montane Riparian Woodland and Shrubland.  Montana Field Guide.  Retrieved on September 17, 2014, from http://FieldGuide.mt.gov/displayES_Detail.aspx?ES=9155
 
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