Montana Field Guide

This is a locally restricted though ecologically important group in Montana. In Montana, these shrub and herbaceous-dominated communities occur only on sandy sites in the Centennial Valley in the extreme southwestern portion of the state. They occur on both active and stabilized dunes and are characterized by open to sparse (gen <15% total cover) shrub and/or herbaceous vegetation. Some characteristic species include Indian Ricegrass (Oryzopsis hymenoides), Sand Wildrye (Elymus flavescens), Scurfpea (Psoralidium sp), and Rabbitbrushes (Chrysothamnus, Ericameria). Elevations of this type in Montana are from 6,600-7,000 feet with a cool, semi-arid continental climate. Soils range in texture from sand to sandy loams. The specific characteristics of this group in terms of the vegetation communities and dominant species that compose it in Montana in contrast to areas outside of the state requires additional documentation.

This Group includes some communities contained within the Active and Stabilized Dune Ecological System.

Sparsely Vegetated; Sandy Soils; Centennial Sandhills; Herbaceous and Short-Shrub Communities

Characteristic Species: Sand Wildrye (Elymus flavescens), Indian Ricegrass (Oryzopsis hymenoides)

In Montana, this group is restricted to the Centennial Sandhills Region in the Centennial Valley of Beaverhead County.

In Montana, G775 occurs in Level IV Ecoregions: 17af (Centennial Basin)

In Montana, G775 occurs within these Major Land Resource Areas: 44B - Central Rocky Mountain Valleys

Large Patch

This group occurs on sandy sites in the intermountain western U.S. from the Columbia Basin, Great Basin, Centennial Valley in Montana, Wyoming Basins, Colorado Plateau and the San Luis Valley of southern Colorado. Elevations of this type in Montana are from 6,600-7,000ft. Sites occur on active and stable dunes though ours are primarily on stabilized dunes. Vegetation communities range from early-seral communities that colonize bare sand to more stable vegetation communities, particularly on dune margins where gradation into adjacent communities occur. Climate at these sites is a cool, semi-arid continental climate. Soils range in texture from sand to sandy loams.

This group is characterized by an open to sparse (<15% total cover) shrub and/or herbaceous layer. Vegetation cover is sparse and composed of xeromorphic shrubs and dwarf-shrubs and/or a short herbaceous layer that is typically sparse and is dominated by perennial graminoids. The composition of plant species present in Montana Intermountain Sand Dune communities may differ from those in other areas. The Centennial Sandhills Complex is listed as supporting the following plant associations: Artemisia tridentata ssp. tridentata/Festuca idahoensis, Artemisia tridentata (ssp. tridentata)/Stipa comata, Elymus lanceolatus/Phacelia hastata, Stipa comata/Psoralea tenuiflora, Artemisia tripartita/Festuca idahoensis, Artemisia tripartita/Stipa comata, Chrysothamnus viscidiflorus/Stipa comata, and Stipa comata-Psoralidium tenuiflorum (Lesica and Korb 2011; Cooper, S.V., C. Jean, and B.L. Heidel 1999). However, several of these associations are placed into groups other than G775. In contrast to the plant associations listed above, the current NVC classification lists only an Achnatherum hymenoides (syn: Oryzopsis hymenoides)-Psoralidium lanceolatum Grassland Association for Montana. The discrepancy in listed vegetation types and the likely dominant species occurring in Montana Intermountain Sand Dune communities requires additional review.

These sites provide important habitat for several Montana Plant Species of Concern, including Astragalus ceramicus var. apus, Cryptantha fendleri, Sand Wildrye (Elymus flavescens), and Pale Evening-primrose (Oenothera pallida ssp. pallida).

In Montana, this group is represented by 1 Alliance and 1 Association within the National Vegetation Classification. Additional plant associations are likely present within this group that are either undescribed or not attributed to Montana.

This vegetation type occurs primarily on recent sand deposits. Dunes may gradually become stabilized by vegetation when disturbance such as fire are removed from the landscape. Over time, if deposition slows, it will succeed to other shrubland or grassland vegetation types.

K.A. Schulz 2015

S. Mincemoyer

12/4/2024