Physiognomy and Structure: This broadly defined savanna and woodland macrogroup has a relatively short (3-10 m tall), open to moderately dense canopy of trees (10-60% cover) with an understory dominated by shrubs or grasses. It encompasses savanna that has widely spaced, short (2-10 m tall), mature (>150-year-old) trees with a moderately dense to dense herbaceous layer dominated by perennial graminoids. More recent invasive juniper savanna stands are characterized by younger, shorter (<3 m tall) pointed-crown trees of low density. Woodland stands have an open to closed tree layer 3-10 m tall with an understory characterized by a shrub and/or herbaceous layers, which are variable and may be sparse to dense or absent. Closed canopies with a sparse understory are not uncommon where fires are suppressed.

Floristics: Diagnostic and dominant trees are Juniperus monosperma and/or Pinus edulis. Juniperus scopulorum may replace Juniperus monosperma and dominate or codominate the canopy at higher elevations. Juniperus osteosperma may replace Juniperus monosperma and codominate the tree canopy with Pinus edulis in the Colorado Plateau and western slope of the southern Rocky Mountains. Juniperus osteosperma stands lacking Pinus edulis are included in ~Intermountain Singleleaf Pinyon - Utah Juniper - Western Juniper Woodland Macrogroup (M026)$$. Understory layers are variable and may be dominated by shrubs, graminoids, or be absent. Associated species include floristic elements from the western Great Plains, southern Rocky Mountains, and Colorado Plateau. Common shrub species include Arctostaphylos patula, Artemisia bigelovii, Artemisia tridentata, Atriplex canescens, Cercocarpus intricatus, Cercocarpus montanus, Coleogyne ramosissima, Ericameria nauseosa, Fallugia paradoxa, Gutierrezia sarothrae, Purshia stansburiana, Purshia tridentata, Quercus gambelii, Quercus x pauciloba, Ribes cereum, Rhus trilobata, Yucca baccata, Yucca glauca, and the ruderal subshrub Gutierrezia sarothrae. The most frequent succulents are Cylindropuntia imbricata, Opuntia phaeacantha, Opuntia polyacantha, Yucca baccata, and Yucca glauca. The herbaceous layer ranges from moderately dense to sparse depending on overstory and substrate and is typically dominated by perennial grasses. The herbaceous layer ranges from moderately dense to sparse and is typically dominated by perennial grasses. Bouteloua curtipendula, Bouteloua gracilis, Hesperostipa comata, and Pleuraphis jamesii are most common with Achnatherum nelsonii, Achnatherum scribneri, Festuca arizonica, Hesperostipa neomexicana, Koeleria macrantha, Lycurus phleoides, Muhlenbergia torreyi, Piptatheropsis micrantha, Poa fendleriana, Poa secunda, and Pseudoroegneria spicata often present to abundant. Bouteloua eriopoda is a more common grass in the southern extent, and Achnatherum hymenoides, Andropogon hallii, and Muhlenbergia pungens are characteristic of deep sandy sites. Festuca arizonica is restricted to higher elevation sites. Many different lower montane, foothill, and steppe forbs may be present, but generally occur with low cover. Associated species include Astragalus spp., Castilleja integra, Cryptantha cinerea var. jamesii (= Cryptantha jamesii), Eriogonum jamesii, Erigeron divergens, Hymenopappus filifolius, Ipomopsis multiflora, Mentzelia spp., Mirabilis multiflora, and Penstemon spp.

Dynamics:  Pinus edulis is extremely drought-tolerant and slow-growing (Little 1987). It is also non-sprouting and may be killed by fire (Wright et al. 1979, Wright and Bailey 1982a). The effect of fire on a stand is largely dependent on tree height and density, fine-fuel load on the ground, weather conditions, and season (Dwyer and Pieper 1967, Wright et al. 1979, Wright and Bailey 1982a). Trees are more vulnerable in open stands where fires frequently occur in the spring, when the relative humidity is low, wind speeds are over 10-20 mph, and there are adequate fine fuels to carry fire (Wright et al. 1979, Wright and Bailey 1982a). Under other conditions, burns tend to be spotty with low tree mortality. Large trees are generally not killed unless fine fuels, such as tumbleweeds, have accumulated beneath the trees to provide ladder fuels for the fire to reach the crown (Jameson 1962). Closed-canopy stands burn infrequently because they typically do not have enough understory or wind to carry fire (Wright et al. 1979). The more open savanna types have a higher amount of herbaceous cover, commonly occur on less steep slopes and have lower erosion rates.

Although Pinus edulis is drought-tolerant, prolonged droughts will weaken trees and promote mortality by secondary agents. Periodic die-offs of pinyon pine caused by insects, such as the pinyon ips beetle (Ips confusus), or fungal agents, such as blackstain root-rot (Leptographium wageneri), tend to be correlated with droughts (Anhold 2005). These mortality events may be localized or widespread but can result in 50 to 90% mortality of Pinus edulis in affected areas (Harrington and Cobb 1988).

In addition, altered fire regimes, cutting trees for fencing or firewood, and improper grazing practices have significant impacts on the quality of sites. Grazing by livestock can modify the fire regime by removing the fine fuels that carry fire. Most pinyon-juniper woodlands in the Southwest have high soil erosion potential. Several studies have measured present-day erosion rates in pinyon-juniper woodlands, highlighting the importance of herbaceous cover and biological soil crusts (Belnap et al. 2001) in minimizing precipitation runoff and soil loss in these woodlands. Fire, livestock grazing, and trampling by recreationalists and vehicles disturb biological soil crusts that help maintain soil structure, reduce soil erosion, provide habitat for plants and preserve biological diversity (Ladyman and Muldavin 1996). More study is needed to understand and manage these woodlands ecologically.

The disturbance type is classified as "High Sun Cold" (summer precipitation and cold climate) distinct from the High Sun Mild of ~Madrean Lowland Evergreen Woodland Macrogroup (M010)$$.