Montana Field Guide

This group contains mostly small and isolated saline marshes and depressional wetlands as well as streamside communities within the Great Plains Region of central and eastern Montana. These are intermittently, seasonally or semi-permanently flooded, usually retaining water into the growing season. Sites have clay soils with an accumulation of salts. They are sparsely to densely-vegetated by herbaceous species tolerant of saline conditions. Typical species include Saltgrass (Distichlis spicata), Western Wheatgrass (Pascopyrum smithii), Nuttall's Alkaligrass (Puccinellia nuttalliana), Foxtail Barley (Hordeum jubatum), Alkali Sacaton (Sporobolus airoides), Cordgrass (Spartina spp), Spikerushes (Eleocharis spp), Western Glasswort (Salicornia rubra), and Black Greasewood (Sarcobatus vermiculatus). The presence and abundance of various species and communities depends in large part on the local hydrology and salinity. Sites occur within the matrix of mixed grass prairie primarily in small depressions and flats. The high salinity of these sites is attributed to the high evaporation and the accumulation of minerals dissolved in the water. Wetlands in this system are discharge wetlands, where water high in dissolved salts has moved from the regional groundwater system into the depression. Hydroperiods vary depending on precipitation and snowmelt, which are the primary sources of water. Water is prevented from percolating out of the depression due to impermeable dense clay, and salt encrustations can occur on the surface with drying.

This Group encompasses portions of the Emergent Marsh, Great Plains Closed Depressional Wetland, Great Plains Saline Depression Wetland, and the Greasewood Flat Ecological Systems.

Saline Wetlands; Marsh and Wet Meadow; Herbaceous or Shrub Dominated; Great Plains Region; Seasonally, Vernally or Permanently Saturated; Hydric Soils; High Clay Contents.

Typical Dominants: Saltgrass (Distichlis spicata), Western Wheatgrass (Pascopyrum smithii), Nuttall's Alkaligrass (Puccinellia nuttalliana), Foxtail Barley (Hordeum jubatum), Alkali Sacaton (Sporobolus airoides), Cordgrass (Spartina spp), Spikerushes (Eleocharis spp), Western Glasswort (Salicornia rubra), Black Greasewood (Sarcobatus vermiculatus)

This wetland group occurs throughout the Great Plains Region in Montana, excluding areas in or adjacent to the island mountain ranges.

In Montana, G984 occurs in Level III Ecoregions: 42 (Northwestern Glaciated Plains) and 43 (Northwestern Great Plains).

In Montana, G984 occurs or potentially occurs within these Major Land Resource Areas: 46 - Northern and Central Rocky Mountain Foothills, 52 - Brown Glaciated Plains, 53A - Northern Dark Brown Glaciated Plains, 53B - Central Dark Brown Glaciated Plains, 54 - Rolling Soft Shale Plain, 58A,B,C,D - Northern Rolling High Plains, 60A,B - Pierre Shale Plains.

Small Patch

These Great Plains sites are distinguished by brackish water caused by strongly saline and alkaline soils. Many of the sites are depressional wetlands though others are found in playas and on stream terraces that are temporarily flooded for part of the growing season. Sites are flat to gently sloping on any aspect. Substrates are moderately saline, often poorly drained, ranging in soil texture from clay and silty clay to silty loam and sandy loam with a clay subsoil (Hanson and Whitman 1938, Johnston 1987, Jones and Walford 1995). The high salinity of these sites is attributed to excessive evaporation and the accumulation of minerals dissolved in groundwater discharge. Water is prevented from percolating out of the depression due to an impermeable dense clay soil. Salt encrustations can occur on the surface due to slow water movement (Hansen et al, 1995). On the Blackfeet Indian reservation, water samples collected from saline depressions had conductivity values that ranged from 1,550-40,000 uhmos/cm (Lesica and Shelley, 1988). The climate in the Great Plains of Montana is temperate continental, semi-arid to subhumid. Much of the precipitation falls during the winter and spring as snow or rain. Summer precipitation falls as rain during convective thunderstorms.

Sites are sparsely to densely vegetated by herbaceous species tolerant of saline conditions. Some areas may be dominated by halophytic forbs or shrubs. The presence and abundance of various species and communities depends in large part on the local hydrology and salinity. Typical species include Saltgrass (Distichlis spicata), Western Wheatgrass (Pascopyrum smithii), Nuttall's Alkaligrass (Puccinellia nuttalliana), Foxtail Barley (Hordeum jubatum), Alkali Sacaton (Sporobolus airoides), Cordgrass (Spartina spp), Spikerushes (Eleocharis spp), Western Glasswort (Salicornia rubra), and Black Greasewood (Sarcobatus vermiculatus). Sites occur within the matrix of mixed grass prairie primarily in small depressions and flats, though also in playas and on stream terraces that are temporarily flooded for part of the growing season. Total vegetation cover (density and height), species composition, and soil salinity depend on the amount and timing of precipitation and flooding. In playas, growth-inhibiting salt concentrations are diluted when the soil is saturated allowing the growth of less salt-tolerant species. As the saturated soils dry, the salt concentrates until it precipitates on the soil surface (Dodd and Coupland 1966). Vegetation forms zones at some saline sites, where species abundance is stratified by salt tolerance.

Communities within this group in Montana are classified into 4 Alliances and 7 Associations within the National Vegetation Classification. These are relatively well-described vegetation communities and likely cover the range of types present.

These sites and communities are controlled by topographic, soils and hydrological factors. The temporary flooding regime combined with high evaporation rates in these dry climates causes accumulations of soluble salts in the soil. Precipitation and climatic patterns greatly affect the vegetation communities at these sites as precipitation and snowmelt transport salts to the depressions and can dilute the soil solution while temperature and wind influence the rate of evapotranspiration. Increased precipitation and/or runoff can dilute the salt concentration and allow for less salt-tolerant species to occur while increased evapotranspiration increases soil salinity leading to a more brackish habitat type.

Management activities should focus on maintaining local hydrological regimes. Activities in adjacent upland sites may also impact these saline wetlands.

In saline depression wetland systems where water has been drained or altered, the original hydrology of the system must be restored. If hydrology is restored, re-growth and re-colonization from the seedbanks and from dormant rhizomatous root systems of common emergent species can occur during periods of flooding. Cattle grazing should be deferred or controlled to allow regrowth, recolonization and resprouting from existing root systems. Annuals such as Western Glasswort (Salicornia rubra) and annual Goosefoots (Chenopodium spp) require periods of inundation and drawdown to initiate germination and to complete their life cycles at the end of the growing season.

Cooper, S.V. et al. (2023)

S. Mincemoyer

12/5/2024