Montana Field Guide

This group of forested riparian communities is extensive in Montana, occurring in mountainous areas across the state on both sides of the Continental Divide. West of the Divide it occurs in some of the forested valley bottoms and foothills up to the subalpine zone. East of the Divide it occurs in all the island ranges, and from the southwest mountains to the hills near Ashland in southeast Montana. It encompasses the majority of forested riparian sites occurring in the mountainous areas of the state excluding the Black Cottonwood/Balsam Poplar communities of G796 and the swampy forested sites of G505. Sites may be dominated or co-dominated by a wide range of coniferous trees, Narrowleaf Cottonwood (Populus angustifolia) and/or Quaking Aspen (Populus tremuloides). Coniferous species that may form riparian communities within this group include Grand Fir (Abies grandis), Subalpine Fir (Abies lasiocarpa), Engelmann Spruce (Picea engelmannii), Ponderosa Pine (Pinus ponderosa), Douglas-fir (Pseudotsuga menziesii), and Rocky Mountain Juniper(Juniperus scopulorum). As a result, this group spans a large elevational range from a low of approximately 2,500ft in northwest Montana to almost 9,000ft in the southern mountains. Other environmental and site characteristics also vary widely. Communities in this group are confined to riparian environments occurring on floodplains or terraces of rivers and streams, in V-shaped, narrow valleys and canyons (where there is cold-air drainage). Less frequently, occurrences are found on large floodplains along rivers in moderately wide valley bottoms, on pond or lake margins, and along seeps on gentle to moderate slopes.

This Group is similar to the Rocky Mountain Subalpine-Montane Riparian Woodland Ecological System.

Riparian & Wetland Forest; Rocky Mountain Region; Montane and Subalpine Zones; Deciduous and Coniferous Trees

Typical Dominants: Grand Fir (Abies grandis), Subalpine Fir (Abies lasiocarpa), Engelmann Spruce (Picea engelmannii), Ponderosa Pine (Pinus ponderosa), Douglas-fir (Pseudotsuga menziesii) Narrowleaf Cottonwood (Populus angustifolia), Quaking Aspen (Populus tremuloides), Rocky Mountain Juniper(Juniperus scopulorum)

This group has an extensive range in Montana occurring in mountainous areas across the state on both sides of the Continental Divide. West of the Divide it occurs in some of the forested valley bottoms and foothills up to the subalpine zone. East of the Divide it occurs in all the island ranges, and from the southwest mountains to the hills near Ashland in southeast Montana.

In MT, G506 occurs within these Level III Ecoregions: 15 (Northern Rockies), 16 (Idaho Batholith), 17 (Middle Rockies), 41 (Canadian Rockies) and portions of 42 (Northwestern Glaciated Plains) and 43 (Northwestern Great Plains).

In Montana, G506 occurs within these Major Land Resource Areas: 43A - Northern Rocky Mountains, 43B - Central Rocky Mountains; 44A - Northern Rocky Mountain Valleys, 44B - Central Rocky Mountain Valleys, 46 - Northern and Central Rocky Mountain Foothills, and portions of 52 - Brown Glaciated Plains, 58A,B - Northern Rolling High Plains.

Small Patch and Large Patch

This group of forested riparian communities occurs in mountainous areas across the state on both sides of the Continental Divide from forested valley bottoms and foothills up to the subalpine zone. Communities in this group are confined to riparian environments occurring on floodplains or terraces of rivers and streams, in V-shaped, narrow valleys and canyons (where there is cold-air drainage). Less frequently, occurrences are found on large floodplains along rivers in moderately wide valley bottoms such as the South Fork of the Flathead River, on pond or lake margins, and along seeps on gentle to moderate slopes. It encompasses the majority of forested riparian sites occurring in the mountainous areas of the state and spans a large elevational range from a low of approximately 2,500ft in northwest Montana to almost 9,000ft in the southern mountains. Other environmental and site characteristics also vary widely.

Riparian sites in this group may be dominated or co-dominated by a wide range of coniferous trees, Narrowleaf Cottonwood (Populus angustifolia) and/or Quaking Aspen (Populus tremuloides). Coniferous species that may form riparian communities within this group include Grand Fir (Abies grandis), Subalpine Fir (Abies lasiocarpa), Engelmann Spruce (Picea engelmannii), Ponderosa Pine (Pinus ponderosa), Douglas-fir (Pseudotsuga menziesii), and Rocky Mountain Juniper (Juniperus scopulorum). Mature stands may be open to dense and of medium-stature (Rocky Mountain Juniper) or more commonly tall trees. Sites range from relatively dry, riparian habitats such as in Rocky Mountain Juniper or Ponderosa Pine communities to more mesic sites with lush, shrubby or herbaceous undergrowth. Due to the wide variety of riparian sites encompassed within this group and the large elevational range, the shrub and herbaceous component may be comprised of a very wide range of species. Individual plant community descriptions should be consulted for species associated with particular riparian habitats.

In Montana, this group includes 7 Alliances and 20 Associations within the National Vegetation Classification. However, 1 Alliance and Association, the Thuja plicata - Tsuga heterophylla Rocky Mountain Riparian Forest Alliance (A4432) and the Thuja plicata / Gymnocarpium dryopteris Riparian Forest Association (CEGL000476) are essentially identical to the Tsuga heterophylla / Gymnocarpium dryopteris Forest Association (CEGL000494) in G217 Cedar - Hemlock Forest and likely should be grouped with it. They are probably best treated within G217 as they both occur on lower to mid slopes or in the drier portions of the riparian zone.

These mostly streamside and floodplain communities are often subject to periodic flooding and fluctuating water tables. Accumulation of winter snowpack, sometimes far upstream and the associated spring runoff are vitally important to the hydrology of these systems.

Grazing along narrow, low order streams can result in increased erosion and channel downcutting (Mitsch and Gosellink 2000). Sites that are subjected to heavy grazing practices may transition to an herbaceous understory consisting of introduced grasses and forbs such as Kentucky bluegrass (Poa pratensis) and Canadian thistle (Cirsium arvense). In addition, fire suppression, timber harvest and reduced flood frequency can affect the succession of riparian communities.

Restoration strategies are dependent on the degree and type of disturbance event. Restoration efforts must first concentrate on restoring the stream's hydrology, if that has been adversely impacted. In-stream habitat enhancement (e.g., additions of logs or boulders) can be employed after restoring natural processes or where short-term improvements in habitat are needed (e.g., for species in recovery).

Removing or strictly limiting grazing by livestock will allow the system to recover if hydric soils have not been lost due to extensive soil compaction, pugging, or down cutting of stream channels, and if there are existing populations of herbaceous, native species (Carex, Juncus, and native grasses) that possess rhizomatous root systems capable of re-colonizing bare soils. Rhizomatous, highly adaptable exotic grasses such as Kentucky bluegrass, common timothy and smooth brome and pasture forbs such as clovers (Trifolium species) and common dandelion (Taraxacum officinale) may persist on the site and compete with existing populations of native graminiods and forbs. Grazing should be excluded for several years to allow adequate re-growth and recovery of existing shrubs and the herbaceous understory.

Most shrub species within these riparian systems are capable of re-sprouting and typically possess extensive, spreading root systems, minimizing additional restoration needs. Vigor, health and degree of vegetative regeneration of existing trees and shrubs must be evaluated to determine if these components of the community are capable of recovery in an acceptable time frame. Intensive revegetation efforts should be limited to sites where catastrophic wildfire or prolonged heavy grazing has destroyed existing trees, shrubs and the seed bank.

G. Kittel (2015)

S. Mincemoyer, L. Vance, C. McIntyre, T. Luna

12/6/2024