This ecological system occurs most frequently on moderately steep to very steep slopes in the mountain ranges of southwestern Montana, but extends as far north as the northern foothills of the Elkhorn Range and as far east as the Wolf Mountains on the Crow Indian Reservation. It occurs on rocky outcrops on south and southwestern aspects at 1,060-2,260 meters (3,500-7,400 feet) and forms small- to large-patch stands on dry and rocky soils. In Montana, this shrubland system is dominated by curl-leaf mountain mahogany (Cercocarpus ledifolius). Rocky Mountain juniper (Juniperus scopulorum) occurs throughout this system’s range and Utah juniper (J. osteosperma) occurs 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. Other co-dominant shrubs include mountain big sagebrush (Artemisia tridentata ssp. vaseyana), antelope bitterbrush (Purshia tridentata) and rubber rabbitbrush (Ericameria nauseosa). Other low shrubs such as snakeweed (Gutierrezia sarothrae) and fringed sage (Artemisia frigida) are common. Undergrowth is dominated by bunchgrasses, usually bluebunch wheatgrass (Pseudoroegneria spicata), needle and thread (Hesperostipa comata), Indian ricegrass (Achnatherum hymenoides) or Idaho fescue (Festuca idahoensis). Curl-leaf mountain mahoganyis a slow-growing, drought-tolerant species that generally does not re-sprout after fire. Prolonged drought, potential for increased fire severity and exotic species invasion are changing the dynamics of this system.
Forest and Woodland, vegetation cover greater than 10%, Montane to foothill elevations, Cercocarpus ledifolius
This shrubland system is dominated by curl-leaf mountain mahogany (Cercocarpus ledifolius). Rocky Mountain juniper (Juniperus scopulorum) occurs throughout this system’s range and Utah juniper (J. osteosperma) occurs 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. Ponderosa pine stands within this system are mostly found in eastern Montana. Other co-dominant shrubs include mountain big sagebrush (Artemisia tridentata ssp. vaseyana), antelope bitterbrush (Purshia tridentata), and rubber rabbitbrush (Ericameria nauseosa). Other low shrubs such as snakeweed (Gutierrezia sarothrae) and fringed sage (Artemisia frigida) are common. Undergrowth is dominated by bunchgrasses, usually bluebunch wheatgrass (Pseudoroegneria spicata), needle and thread (Hesperostipa comata), and Indian ricegrass (Achnatherum hymenoides).Other low shrubs such as broom snakeweed (Gutierrezia sarothrae) and fringed sage (Artemisia frigida) are common (Mueggler and Stewart, 1980).
Bluebunch wheatgrass (Pseudoroegneria spicata) is the dominant grass throughout this system, although needle and thread (Hesperostipa comata) and Indian ricegrass (Achnatherum hymenoides) may be co-dominant on more xeric occurrences. 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 rosy pussytoes (Antennaria rosea), sulphur buckwheat (Eriogonum umbellatum), few-seed draba (Draba oligosperma), tufted fleabane (Erigeron cespitosus), Hood’s phlox (Phlox hoodii), and stoneseed (Lithospermum ruderale). Cacti such as plains pricklypear (Opuntia polyacantha)and Missouri foxtail cactus (Mammillaria missouriensis) are present on especially xeric sites. Within this system, cheatgrass (Bromus tectorum) or other annual bromes and invasive weeds can be abundant.
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. High-intensity fires kill all standing shrubs and may also eliminate the seed bank on these sites. However, a lack of continuous fuels, sparse undergrowth, open stand structure, and low downed wood accumulations contribute to a low fire frequency within this system. Particularly in areas where fire has been suppressed, the absence of fire in curl-leaf mountain mahogany habitats has increased curl-leaf mountain mahogany abundance and successful regeneration in some areas of central, southwestern, and southeastern Montana (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 it in spring, fall, and/or winter, but rarely in the summer. In other areas of this system’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 cheatgrassare 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 increase in the cover of prairie junegrass and needle and thread. Unpalatable shrubs 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 maculosa), or other noxious species capable of colonizing dry, rocky soils.
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 the 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. 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. 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 wheatgrassseedlings 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.
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