Montana Field Guide

This low to tall shrub community occurs most frequently on moderately steep to very steep slopes or on ridgelines in the foothills and mountains of southwest and southcentral Montana. It extends as far north as Helena and as far east as the Wolf Mountains on the Crow Indian Reservation. It occurs primarily on south and southwestern aspects from 4,000-7,000 feet on limestone parent materials where it forms small- to large-patches on dry and rocky soils. In Montana, this shrubland system is defined solely by the dominance of curl-leaf mountain mahogany (Cercocarpus ledifolius). Rocky Mountain juniper (Juniperus scopulorum) may occur as scattered individuals in some communities and Utah juniper (J. osteosperma) may be present in some stands in the Pryor Mountains. Scattered conifers such as Douglas-fir (Pseudotsuga menziesii), limber pine (Pinus flexilis) and ponderosa pine (P. ponderosa) may also occur in some stands. This community provides important winter range for deer and elk.

This Group is equivalent to the Mountain Mahogany Woodland and Shrubland Ecological System.

Shrubland; Vegetation Cover >10%; Foothill and Montane Zones; Rocky, Exposed Sites; Rocky Mountain and Intermountain Regions

Typical Dominants: Curl-leaf Mountain-mahogany (Cercocarpus ledifolius)

Most common in the foothills and mountain ranges of southwestern Montana and in the vicinity of the Pryor and Bighorn Mtns in Carbon and Big Horn Counties. It extends as far north as the northern foothills of the Elkhorn Range and in the vicinity of the Helena Valley. It occurs as far east as the Wolf Mountains on the Crow Indian Reservation. Small occurrences are known from the southern portion of Ravalli County in the vicinity of the Bitterroot Valley. Elsewhere in the western United States, this type occurs in hills and mountain ranges of the Intermountain West to the eastern foothills of the Sierra Nevada.

In Montana, G249 occurs within these Level III Ecoregions: 17 (Middle Rockies) and 18 (Wyoming Basin). Minor amounts also occur in 43n - Montana Central Grasslands and 43v - Pryor-Bighorn Foothills within the Northwestern Great Plains Ecoregion.

In Montana, G249 occurs within these Major Land Resource Areas: The southern half of 43B - Central Rocky Mountains, the southern portion of 46 - Northern and Central Rocky Mountain Foothills

Small Patch and Large Patch

This vegetation type occurs as small- to large-patches on dry and rocky soils associated with moderately steep to very steep slopes and on ridgelines. It is most prevalent on limestone outcrops where extensive stands develop, although it also occurs on other parent materials, generally as small patches. It can occur on all aspects but is most prevalent on south and southwestern aspects. These communities range in elevation within the state from 4,000-7,000 feet. Climate within its range in Montana is typical of mid-continental regions with long severe winters and hot, dry summers.

This shrubland community is dominated by curl-leaf mountain mahogany (Cercocarpus ledifolius). Rocky Mountain juniper (Juniperus scopulorum) may occur as scattered individuals in some communities and Utah juniper (J. osteosperma) may be present in some stands in the Pryor Mountains. Conifers such as Douglas-fir (Pseudotsuga menziesii), limber pine (Pinus flexilis) and ponderosa pine (P. ponderosa) may also occur in some stands. Mountain big sagebrush (Artemisia tridentata ssp. vaseyana) and antelope bitterbrush (Purshia tridentata) occur in some stands. Subshrubs such as snakeweed (Gutierrezia sarothrae) and fringed sage (Artemisia frigida) are common components. Undergrowth is dominated by bunchgrasses, usually bluebunch wheatgrass (Pseudoroegneria spicata), needle and thread (Stipa comata), Indian ricegrass (Achnatherum hymenoides) or Idaho fescue (Festuca idahoensis) (Mueggler and Stewart, 1980).

Bluebunch wheatgrass (Elymus spicatus) is the dominant grass throughout this system, although Needle-and-Thread (Stipa comata) and Indian ricegrass (Oryzopsis hymenoides) may be co-dominant on more xeric sites. Mesic occurrences are frequently dominated or co-dominated by Idaho fescue (Festuca idahoensis). Prairie junegrass (Koeleria macrantha) is a minor component. Due to the rocky and shallow substrates, undergrowth cover is relatively sparse, often with less than 20% cover. Common forbs include species of pussytoes (Antennaria sp), buckwheat (Eriogonum sp), few-seed draba (Draba oligosperma), tufted fleabane (Erigeron cespitosus), and phlox (Phlox sp). Cacti such as plains pricklypear (Opuntia polyacantha) and Missouri foxtail cactus (Coryphantha missouriensis) are present on especially xeric sites. Cheatgrass (Bromus tectorum) or annual bromes may be common at some sites.

Curl-leaf mountain mahogany is easily killed by fire at all intensities. Some shrubs may re-sprout following low-intensity fires, but these are typically low in vigor and do not persist. Regeneration is by seedling recruitment. Post-fire regeneration may be quick unless fire intensity is severe and has destroyed the local seedbank. High-intensity fires kill all standing shrubs and may also eliminate the seed bank (Gucker 2006). However, a lack of continuous fuels, sparse undergrowth, open stand structure, and low downed woody accumulations generally results in low fire frequency within these communities. Fire return intervals currently range from 70 to 110 years with the majority of fires being mixed severity (U.S. Department of Agriculture 2012). Prior to 1900, fire return intervals are estimated to have been much shorter but have increased due to fire suppression and heavy livestock grazing, reducing fine fuel loads (Gucker 2006). The absence of fire in curl-leaf mountain mahogany habitats in central, southwestern, and southeastern Montana has in some instances increased curl-leaf mountain mahogany abundance and regeneration success (Gruell 1982).

Curl-leaf mountain mahogany provides food and cover for a variety of wildlife species such as deer and elk. Some livestock (domestic goats, sheep, and cattle) use these communities in spring, fall, and/or winter, but rarely in the summer. In other areas of this community’s geographic range, heavy grazing practices have been observed to lead to a decrease in associated grasses and an increase in the spread of cheatgrass (Bromus tectorum) (Young 1989). Thus, sites invaded by cheatgrass are changing the dynamics of this system by increasing fire potential, severity, and spread.

Excessive grazing can lower the cover of the most common perennial bunchgrasses in this system and lead to an increase in the cover of prairie junegrass and needle and thread grass or invasive, annual bromes. Unpalatable subshrubs such as fringed sage or snakeweed also increase under heavy grazing pressure. Severe grazing can lead to an abundance of cheatgrass (Bromus tectorum), spotted knapweed (Centaurea stoebe), or other noxious weeds capable of colonizing dry, rocky soils.

Curl-leaf mountain mahogany is a slow-growing, drought-tolerant species that generally does not re-sprout after fire. Prolonged drought, the potential for increased fire severity and exotic species invasion are changing the dynamics of these communities. Prescribed fire exposes mineral soils which promote seedling establishment and may be used for stands in which fuel levels are low, and in which cheatgrass is absent. Fire is also recommended for sites in west-central and southwestern Montana to encourage curl-lead mountain mahogany regeneration while slowing succession by shade tolerant Douglas fir (Gucker 2006).

Restoration strategies will depend on the type and intensity of the disturbance, and in the case of fire, on the degree of fire severity and fire recovery objectives. Light or moderately intensive burns can increase cover of native perennial bunchgrasses during the first two years following fire on sites where there was good pre-fire condition with minimal exotic cover. However, severely burned sites will require replanting with curl-leaf mountain mahogany seedlings and other co-dominant shrubs, due to the slow recovery time within this system and low rates of natural seedling recruitment. When planting from seed, cold, moist stratification is required to enhance germination success (Gucker, 2006). Generally, larger container volume of nursery stock results in higher outplanting success; 20-cubic inch container stock is recommended for use on these sites. Curl-leaf mountain mahogany is rated as good to excellent for soil erosion control due to its ability to stabilize soils. Planting rates must be developed on a site-by-site basis to meet management objectives.

Successful restoration of native grasses within this system may be limited to sites where pre-fire cheatgrass cover was low. Fall germination and rapid elongation of roots provide cheatgrass with a competitive advantage over native perennial species (Harris 1967). Cheatgrass reduces growth of bluebunch wheatgrass seedlings and is capable of producing twice the root quantity during the first 45 days of growth (Aguirre and Johnson 1991). Prolific seed production also contributes to the competitive advantage of this species over native grasses. Thus, on sites that are heavily infested with cheatgrass prior to fire, seeding rates must be adjusted to include more competitive native grass species. Some selections of bluebunch wheatgrass that exhibit desirable growth characteristics may have promise for establishing this species on invaded sites.

K.A. Schulz 2015

S. Mincemoyer, L. Vance, T. Luna, M. Hart

12/5/2024