Common (Translated Scientific) Name: Singleleaf Pinyon - Utah Juniper - Western Juniper Intermountain Woodland Macrogroup
Colloquial Name: Intermountain Pinyon - Juniper Woodland
Hierarchy Level: Macrogroup
Type Concept: This broadly defined macrogroup is composed of woodland, savanna and scrub characterized by an open to closed tree canopy of Juniperus occidentalis, Juniperus osteosperma, Pinus monophylla, and/or Cercocarpus ledifolius. Shrub layers are frequently dominated by Artemisia tridentata, which in places can form a moderately dense shrub canopy. Other common associated shrub species include Arctostaphylos patula, Artemisia arbuscula, Artemisia nova, Cercocarpus intricatus, Cercocarpus ledifolius (shrub form), Chrysothamnus viscidiflorus, Coleogyne ramosissima, Ericameria nauseosa, Glossopetalon spinescens, Purshia stansburiana, Purshia tridentata, Quercus chrysolepis, Quercus gambelii, Quercus john-tuckeri, Quercus turbinella, Ribes cereum, Tetradymia spp., and Yucca brevifolia. The herbaceous layer may be sparse to dense depending on overstory density, substrate, landscape position, and disturbance history, with the densest graminoid layer in open tree savanna. Common graminoid associates include Bouteloua gracilis, Carex filifolia, Hesperostipa comata, Festuca idahoensis, Leymus cinereus, Leymus salinus, Pleuraphis jamesii, Pseudoroegneria spicata, Poa fendleriana, and Poa secunda. Forb species may be diverse but typically have low canopy cover values. Pinyon and juniper stands in the Colorado Plateau and Great Basin occur between 1500-2600 m elevation on warm, dry sites of lower mountain slopes, hills, mesas, plateaus, ridges, and more recently on basins and flats where trees are expanding into semi-desert grasslands and steppe. Substrates are variable, but are generally shallow, cobbly, gravelly, or sandy loams to clay loam or clay. Juniper stands in the Columbia Plateau range from under 200 m elevation along the Columbia River in central Washington to over 1500 m. In central Oregon, the center of distribution, they occur on all aspects and slope positions. Cercocarpus ledifolius woodland and scrub stands occur in hills and mountain ranges in the Great Basin and eastern foothills of the Sierra Nevada northeast to the foothills of the Bighorn Mountains. It typically occurs from 600 m to over 2650 m in elevation on rocky outcrops or escarpments and forms small- to large-patch stands. Most stands occur as shrublands on ridges and steep rimrock slopes, but they may be composed of small trees in steppe areas.
Diagnostic Characteristics: This broadly defined macrogroup is composed of woodland, savanna and scrub characterized by an open to closed tree canopy composed of differential and often dominant species of Juniperus occidentalis, Juniperus osteosperma, Pinus monophylla, and/or Cercocarpus ledifolius. The fidelity of Juniperus osteosperma is lower than the other diagnostic species because Juniperus osteosperma also occurs across the western extent of ~Southern Rocky Mountain Two-needle Pinyon - One-seed Juniper Woodland Macrogroup (M027)$$ in the Colorado Plateau and western slope of the Colorado Rocky Mountains with Pinus edulis in this macrogroup. In addition, Juniperus californica is a component in the western Mojave and locally in eastern Mojave mountains. It is considered part of M009 (California woodlands) but its modal expression in the western Mojave and the inner southern Coast Ranges of California is much like other members of M026 (T. Keeler-Wolf pers. comm. 2014). Cercocarpus ledifolius woodland stands are most common at the western extent of the macrogroup often occurring with Juniperus occidentalis or Pinus monophylla stands. Juniperus monosperma is absent except in some transitional stands in northeastern Arizona. In Pinus monophylla-dominated stands across some regions of southern California, Juniperus osteosperma is replaced by Juniperus californica. Pinus jeffreyi may be present on the eastern slope of the Sierra Nevada in California.
Rationale for Nominal Species or Physiognomic Features: Pinus monophylla, Juniperus osteosperma, and Juniperus occidentalis are all high fidelity, differential and typically dominant species of this woodland and savanna macrogroup. However, Cercocarpus ledifolius can also be a diagnostic species, and it also occurs as a shrubland dominant species, having a lower fidelity in this woodland and tree savanna macrogroup. The fidelity of Pinus edulis is lower because it is also a diagnostic species in another macrogroup (M027).
Classification Comments: This macrogroup occurs over a broad biogeographic range and has a broad concept with multiple diagnostic species. The pinyon and juniper diagnostic species are related and occur on relatively dry sites at mid to lower elevations. However, Cercocarpus ledifolius also occurs as seral vegetation in relatively mesic montane sites, often with Abies concolor trees that are colonizing and eventually dominating the site.
This macrogroup (M896) is closely related to Southern Rocky Mountain-Colorado Plateau Two-needle Pinyon - Juniper Woodland Macrogroup (M897), and could be merged (T. Keeler-Wolff pers. comm. 2014), but see comments in M897.
In Wyoming, except for stands in the southwest portion of the state, most juniper woodland stands are likely to be classified in Rocky Mountain Foothill-Rock Outcrop Limber Pine - Juniper Woodland Group (G209) in Central Rocky Mountain Dry Lower Montane-Foothill Forest Macrogroup (M501), rather than Colorado Plateau Pinyon - Juniper Woodland Group (G900) in this macrogroup (M896). More survey and analysis are needed to better describe the geographic boundary between these types.
In addition, the Cercocarpus ledifolius woodland and shrubland alliances are poorly distinguished in the literature, as most authors describe the species as having either a tall-shrub or small-tree growth form within a single association. Some associations may have shrub-dominated stands in one area yet a woodland physiognomy in another. The woodland physiognomy appears to be more typical. Near the northern edge of its range in Montana and Idaho, Cercocarpus ledifolius is described as occurring primarily in the shrub form (Mueggler and Stewart 1980, Tisdale 1986). These northern variants are the only described stands which appear to be clearly distinct from the woodland alliance. The woodland alliance may have a different dominant subspecies (or variety) than the shrubland. Woodland stands tend to occur in the more western portion of the species' range and are largely attributed to Cercocarpus ledifolius var. intercedens (= Cercocarpus ledifolius var. intermontanus), whereas Cercocarpus ledifolius var. ledifolius is found in the eastern and northern portions of the range and typically occurs as a shrubland.
One reviewer recommends moving Intermountain Basins Curl-leaf Mountain-mahogany Woodland & Scrub Group (G249) out of this macrogroup (M896) into Southern Rocky Mountain Montane Shrubland Macrogroup (M049), or at least Cercocarpus ledifolius shrubland stands in California (found in the Sierra Nevada to various desert mountains) that are shrubland, not woodland and are similar to stands of Cercocarpus intricatus in Southern Rocky Mountain Mountain-mahogany - Mixed Foothill Shrubland Group (G276) in M049 (J. Evens pers. comm. 2014). If we follow this recommendation, then we should also consider moving Cercocarpus ledifolius shrubland from the northern extent into a shrubland macrogroup. Splitting the various Cercocarpus ledifolius associations by physiognomy into different groups and macrogroups may create issues with diagnostic species. In addition, some reviewers suggest merging the macrogroup with Southern Rocky Mountain-Colorado Plateau Two-needle Pinyon - Juniper Woodland Macrogroup (M897) because of shared diagnostic species Pinus edulis.
Similar NVC Types:
M010 Madrean Lowland Evergreen Woodland, note: "shares some of the widespread dominant/diagnostic species such as conifer Pinus edulis, although M026 lacks Madrean species that are differential species in M010."
M049 Southern Rocky Mountain Montane Shrubland, note:
M897 Southern Rocky Mountain Two-needle Pinyon - Juniper Woodland, note: may also be dominated or codominated by Pinus edulis.
Physiognomy and Structure: This broadly defined evergreen macrogroup is composed of a woodland, savanna and scrub structure. Stands are typically short (2-10 m tall), with an open to closed, evergreen needle-leaved or scale-leaved or broad-leaved, sclerophyllous tree canopy. The understory is variable with lush grass cover and occasionally scattered shrubs in the savanna stands to a sparse to dense short-shrub layer and/or herbaceous layer in woodland stands. On extremely xeric sites, diagnostic juniper and pinyon trees species may only attain 2 m in height and have a more shrub form. However, Juniperus occidentalis-dominated stands have two different tree canopy structures: (1) an old-growth woodland with large, fairly well-spaced trees with rounded crowns, and (2) relatively young, often dense junipers trees with pointed crowns. The structure of the understory ranges from perennial grass-dominated tree savannas and open woodlands to shrublands with a very open tree canopy (wooded shrublands) and open to moderately dense woodlands with a shrub-dominated understory. Cover of understory species sharply declines when tree canopy cover exceeds 40% (Young et al. 1982). Many of the tree savannas have a sparse shrub layer present. Vegetation structure is variable as Cercocarpus ledifolius stands may form an open to dense short-tree canopy (3-5 m tall), a tall-shrub layer (3-4 m tall), or a short-shrub layer (1-2 m tall). Herbaceous layers are variable depending on the density of woody canopy, substrate, landscape position, and disturbance history. Perennial graminoids typically dominate most herbaceous layer with an often high diversity of species with low cover.
Floristics: This broadly defined macrogroup is composed of woodland, savanna and scrub characterized by an open to closed tree canopy of Juniperus occidentalis, Juniperus osteosperma, Pinus monophylla, and/or Cercocarpus ledifolius. There is limited overlap between stands dominated by Juniperus occidentalis and Pinus monophylla. Juniperus osteosperma occurs across the ranges of both Pinus edulis and Pinus monophylla in this macrogroup. Cercocarpus ledifolius woodland stands are most common at the western extent of the macrogroup, often occurring with Juniperus occidentalis or Pinus monophylla stands. Juniperus monosperma is absent except in some transitional stands in northeastern Arizona. In Pinus monophylla-dominated stands of some regions of southern California, Juniperus osteosperma is replaced by Juniperus californica. On the east slope of the Sierra Nevada in California, Pinus jeffreyi may be a minor component of these woodlands. The understory is variable and can be characterized by shrubs or graminoids. Shrub layers are frequently dominated by the widespread species Artemisia tridentata forming a moderately dense shrub layer. Other common associated shrub species include Arctostaphylos patula, Artemisia arbuscula, Artemisia nova, Cercocarpus intricatus, Cercocarpus ledifolius (shrub form), Chrysothamnus viscidiflorus, Coleogyne ramosissima, Ephedra viridis, Ericameria nauseosa, Garrya flavescens, Glossopetalon spinescens, Purshia stansburiana, Purshia tridentata, Quercus chrysolepis, Quercus gambelii, Quercus turbinella, Ribes cereum, Ribes velutinum, Symphoricarpos spp., Tetradymia spp., Yucca baccata, and Yucca brevifolia. The herbaceous layer may be sparse to dense depending on overstory density and substrate with the densest graminoid layer in open tree savanna. Common graminoid associates include Achnatherum speciosum, Bouteloua gracilis, Bouteloua eriopoda, Carex filifolia, Elymus elymoides, Festuca idahoensis, Hesperostipa comata, Leymus cinereus (= Elymus cinereus), Leymus salinus, Pleuraphis jamesii, Pseudoroegneria spicata, Poa fendleriana, and Poa secunda. Non-natives, including Bromus rubens and Bromus tectorum, have invaded some stands. Forb species may be diverse but typically have low canopy cover values.
Dynamics: Periodic fire (at a 10- to 30-year interval) is important in maintaining the juniper savanna structure (Wright et al. 1979, West and Young 2000). Juniper trees less than 1.2 m (4 feet) tall are readily killed by fires (Wright et al. 1979). Heavy grazing by livestock reduces the fine fuel layer (grasses), which decreases the fire frequency, resulting in increased juniper density (Wright et al. 1979, West and Young 2000). Over the last century, a reduction in fire frequency has caused a conversion of some juniper savanna to juniper woodland, as well as invasion of juniper trees from areas of naturally low fire frequency, e.g., rocky ridges into adjacent communities, especially sagebrush steppe (Wright et al. 1979, West and Young 2000, Romme et al. 2009). In contrast, woodland stands of Juniperus osteosperma and Pinus monophylla are not maintained by frequent fire (historic return intervals are >100 years), since fires kill small to larger trees in stands and trees slowly regenerate from seed. Instead, periodic fire poses a risk to their stands because non-native grasses can invade in burned areas and promote increased fire frequency by providing fuels that spread fire (J. Evens pers. comm. 2014).
Environmental Description: This broadly defined woodland, savanna and scrub macrogroup is found in the interior western U.S. Single-leaf pinyon and juniper stands in the Colorado Plateau and Great Basin occur between 1500-2600 m elevation on warm, dry sites on lower mountain slopes, hills, mesas, plateaus, ridges, and more recently on basins and flats where trees are expanding into semi-desert grasslands and steppe. Substrates are variable, but are generally calcareous and alkaline, and often shallow and rocky, but may be acidic in places. Soils texture ranges from stony, cobbly, gravelly, or sandy loams to clay loam or clay. Juniper stands in the Columbia Plateau range from under 200 m elevation along the Columbia River in central Washington to over 1500 m. In central Oregon, the center of distribution across the Columbia Plateau, the type occurs on all aspects and slope positions. Old-growth stands are largely restricted to rocky outcrops, upper slopes and ridges, and rims of mesas and canyons that are fire-safe. Younger seral stands have invaded adjacent shrublands and grasslands in recent times and now occur on lower slopes, valleys and plains. Cercocarpus ledifolius woodland and scrub stands occur in hills and mountain ranges of the Great Basin and eastern foothills of the Sierra Nevada northeast to the foothills of the Bighorn Mountains. They typically occur from 600 m to over 2650 m in elevation on rocky outcrops or escarpments and form small- to large-patch stands in forested areas. Most stands occur as shrublands on ridges and steep rimrock slopes, but they may be composed of small trees in steppe areas. In the Great Basin and Colorado Plateau where juniper and pinyon tree are both present, pinyon tend to occur at higher elevations.
Geographic Range: This broadly defined woodland, scrub and tree savanna macrogroup occupies the interior western U.S. from the Western Slope of Colorado and northwestern corner of New Mexico east into the Colorado Plateau, and Great Basin to the eastern foothills of the Sierra Nevada extending southwest in California to the northern Transverse Ranges (Ventura County) and San Jacinto Mountains (Riverside County), and north into the Modoc Plateau of northeastern California and along the eastern foothills of the Cascades, south-central Washington, and southern Idaho and east to the foothills of the Bighorn Mountains.
States/Provinces: AZ, CA, CO, ID, MT, NM, NV, OR, UT, WA, WY
|US Forest Service Ecoregions (2007)|
Confidence Level: Moderate
Confidence Level Comments:
Intermountain Singleleaf Pinyon - Juniper Woodland, note: M026 replaced by M896
Synonomy: > Juniperus occidentalis Zone (Franklin and Dyrness 1973)
> Curlleaf Mountain-Mahogany (415) (Shiflet 1994)
> Curlleaf Mountain-Mahogany - Bluebunch Wheatgrass (322) (Shiflet 1994)
>< Juniper - Pinyon Pine Woodland (504) (Shiflet 1994)
>< Juniper - Pinyon Woodland (412) (Shiflet 1994)
>< Juniper steppe woodland (Juniperus - Artemisia - Agropyron) (Küchler 1964)
>< Juniper-Pinon Savannas and Woodlands of Western North America (412) (West 1999a)
>< Juniper-Pinyon woodland (Küchler 1964)
> Northern Juniper Woodlands (Holland and Keil 1995)
> PIMO Series (West et al. 1998)
> Pinon-Juniper Woodlands (West and Young 2000)
>< Pinyon - Juniper: 239 (Eyre 1980)
> Pinyon Juniper Series, Juniperus osteosperma Association - 122.418 (Brown et al. 1979)
> Pinyon Juniper Series, Pinus monophylla-Juniperus californica - chaparral Association - 122.414a (Brown et al. 1979)
> Pinyon Juniper Series, Pinus monophylla-Juniperus californica Association - 122.411a (Brown et al. 1979)
> Pinyon Juniper Series, Pinus monophylla-Juniperus osteosperma Association - 122.416 (Brown et al. 1979)
> Pinyon Juniper Series, Pinus monophylla Association - 122.417 (Brown et al. 1979)
>< Rocky Mountain Juniper: 220 (Eyre 1980)
> Utah Juniper Series (Dick-Peddie 1993)
> Western Juniper: 238 (Eyre 1980)
Concept Author(s): N.E. West, R.J. Tausch, and P.T. Tueller (1998)
Author of Description: K.A. Schulz and M. Jennings
Version Date: 14May2015
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