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Community Field Guide

Scientific Name:
Salix exigua Mesic Graminoids Shrubland

Common Name:
Sandbar willow / Mesic Graminoid Shrubland

Community Description

Summary:
This riparian association is found primarily in the central Great Plains, but also occurs in parts of the Rocky Mountains and Intermountain semi-desert regions. It generally occurs along backwater channels and other perennially wet but less scoured sites, such as floodplain swales and irrigation ditches. In Nebraska, this community is found on sandbars, islands, and shorelines of stream channels and braided rivers. The vegetation is characterized by the dominance of Salix exigua in the moderately dense tall-shrub canopy with a dense herbaceous layer dominated by graminoids. Other common shrubs include saplings of Populus deltoides or Salix amygdaloides, Salix eriocephala, Salix lutea, and Amorpha fruticosa. Tall perennial grasses can appear to codominate the stand when Spartina pectinata, Panicum virgatum or other tall grasses are present. Other mesic graminoids, such as Carex spp., Eleocharis spp., Juncus spp., Pascopyrum smithii, Schoenoplectus pungens (= Scirpus pungens), and Sphenopholis obtusata, may be present. Common forb species include Bidens spp., Lobelia siphilitica, Lycopus americanus, Lythrum alatum, Polygonum spp., and Xanthium strumarium. Diagnostic features of this association include the nearly pure stands of Salix exigua shrubs, with a dense ground layer of at least 30% cover of mesic graminoids.

Environment:
This riparian association is found primarily in the central Great Plains, but also occurs in parts of the Rocky Mountains and Intermountain semi-desert regions. Elevation ranges from 1750-2700 m (5700-9100 feet). It generally occurs along alluvial terraces of backwater channels and other perennially wet but less scoured sites, such as floodplain swales and irrigation ditches. This community is found on sandbars, islands, and shorelines of stream channels and braided rivers in Nebraska (Steinauer and Rolfsmeier 2000). Stands usually occur within 1 m vertical distance of the stream channel on point bars, low floodplains, terraces and along overflow channels. It can also occur away from the stream channel in mesic swales or along the margins of beaver ponds and seeps. Soils are derived from alluvium and are quite variable in development, ranging from thin (<1 m) and skeletal with depth (10-50% cobbles) to well-developed Mollisols (Kittel et al. 1999). Textures are typically loamy sands interspersed with layers of silty clays and alternating with coarse sands. Upper layers (10-30 cm) often have 25-30% organic matter (Kittel et al. 1999).<

>In Montana, this type occurs on stream terraces and in meadows associated with stream channels from about 2,000 to 7,700 feet. Valley bottoms may be narrow to very wide and of low to moderate gradient. This community is not in the most dynamic portion of the floodplain, as are some of the other Salix exigua types (Padgett et al. 1989). Water tables range from the surface to over 3 feet below the surface. Distinct and prominent mottle is common within 20 inches of the surface, indicating a seasonally high water table. Soils indicate a broad range of development, from the well developed Terric Borohemists, Cumulic Haploborolls, Typic Cryaquolls, and Pachic Cryoborolls to less developed Aquic Cryofluvents and Fluvaquentic Haploxerolls. Soils develop on alluvial depositions of varying ages. Particle-size classes were highly variable, with estimated available water-holding capacity from low to moderate (Padgett et al. 1989).

Vegetation:
This association is characterized by the dominance of Salix exigua in the moderately dense tall-shrub canopy with a dense herbaceous layer dominated by graminoids. Others common shrubs may include saplings of Populus deltoides, Salix amygdaloides, Salix bebbiana, Salix eriocephala, Salix geyeriana, Salix lucida ssp. lasiandra (= Salix lasiandra), Salix lutea, Salix monticola, Salix planifolia, Amorpha fruticosa, or Rosa woodsii. Tall perennial grasses can appear to codominate the stand when Spartina pectinata, Sorghastrum nutans, Panicum virgatum, or other tall grasses are present. Mesic graminoids dominate the diverse understory and include Carex pellita (= Carex lanuginosa), Carex nebrascensis, Carex rostrata, Deschampsia caespitosa, Eleocharis palustris, Elymus canadensis, Equisetum spp., Glyceria spp., Juncus balticus, Juncus longistylis, Juncus tenuis, Juncus torreyi, Luzula parviflora, Pascopyrum smithii, Polygonum spp., Schoenoplectus americanus, Schoenoplectus pungens (= Scirpus pungens), Sphenopholis obtusata, and others. The sparse forb cover may include Lobelia siphilitica, Bidens spp., Geum macrophyllum, Lycopus americanus, Lythrum alatum, Mentha arvensis, Typha angustifolia, Veronica americana, and Xanthium strumarium. Agrostis stolonifera, Bromus inermis, Melilotus spp., Poa pratensis, or Phleum pratense, and other introduced forage species may be present to abundant in disturbed stands of this community. Diagnostic features of this association include the nearly pure stands of Salix exigua shrubs, with a dense ground layer of at least 30% cover of graminoids.

Range:
Stands occur throughout Utah, extreme western Colorado (Padgett et al. 1989) and the Colorado Front Range (Kittel et al. 1998), and throughout Idaho (Padgett et al. 1989; Jankovsky-Jones 1997) and Montana (Hansen et al. 1995).

Dynamics:
Flooding and scouring during spring periods is common. This plant association is considered early-seral typical of recent floodplains and highly disturbed, low, wet areas . The presence of Populus sp. seedlings within this association indicates succession to a cottonwood stand. Overgrazing by livestock will reduce the vigor of Salix exigua and may eventually eliminate it from the site and allow invasion of introduced and non-palatable native species. However, reducing stocking rate will allow Salix exigua to re-establish itself, provided it has not been completely eliminated from the site. (Hansen et al. 1995).

Management:
The rhizomatous graminoid cover in this community result in high soil-holding and streambank stabilization ability. Should the stands become drier and/or grazing levels increase, this type might be replaced by the Salix exigua / Poa pratensis or possibly the Salix exigua / Barren community.

Global Rank: G5 State Rank: S5

Community References

Identifier:
CEGL001203

Author:
mod. K.A. Schulz

Citations:
Bourgeron and Engelking 1994, Cooper and Cottrell 1990, Driscoll et al. 1984, Hansen et al. 1995, Hoagland 1998c, Hoagland 2000, Jones and Walford 1995, Kittel 1994, Kittel and Lederer 1993, Kittel et al. 1996, Kittel et al. 1999, Lauver et al. 1999, Padgett et al. 1988b, Padgett et al. 1989, Steinauer and Rolfsmeier 2000, Walford et al. 2001

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This information is from the:
Montana Natural Heritage Program
Montana State Library--Natural Resource Information System
1515 East Sixth Ave., Helena, MT 59620-1800
406 444-5354
http://mtnhp.org
mtnhp@mt.gov