Physiognomy and Structure: These woodlands are characterized by diagnostic tree species Pinus edulis and Juniperus monosperma that form an open to dense tree layer 3-10 m tall. Shrub and herbaceous layers are variable and may be sparse to dense or absent.

Floristics: This southern Rocky Mountain woodland group is characterized by a relatively short (3-10 m tall), open to moderately dense tree canopy dominated by Pinus edulis and/or Juniperus monosperma. Juniperus scopulorum may codominate or replace Juniperus monosperma at higher elevations. Juniperus monosperma may dominate stands as long as Pinus edulis is present with significant cover. Stands with Juniperus osteosperma are representative of the Colorado Plateau and are not included in this group. In southern transitional areas with ~Madrean Pinyon - Juniper Woodland Group (G200)$$ in central New Mexico, Juniperus deppeana may be present but not dominant. Understory layers are variable and may be dominated by shrubs, graminoids, or be absent. Associated species are generally more typical of the southern Rocky Mountains or Great Plains than the Colorado Plateau. Common species include Artemisia bigelovii, Atriplex canescens, Cercocarpus montanus, Ericameria nauseosa, Fallugia paradoxa, Quercus gambelii, Quercus x pauciloba, Quercus turbinella, Ribes cereum, and grasses such as Achnatherum nelsonii, Achnatherum scribneri, Andropogon hallii, Bouteloua gracilis, Festuca arizonica, Hesperostipa comata, Hesperostipa neomexicana, or Pleuraphis jamesii. Many different foothill and lower montane forbs may be present, but generally with low cover.

Dynamics:  Both Pinus edulis and Juniperus monosperma are relatively short (generally <15 m tall), shade-intolerant, drought-tolerant, slow-growing, long-lived trees (Meeuwig and Bassett 1983, Little 1987, Anderson 2002, Johnson 2002, Romme et al. 2003). Both tree species are also non-sprouting and may be killed by fire (Wright et al. 1979).

Pinyon-juniper woodlands are influenced by drought, fires, grazing, and insect-pathogen outbreaks (West 1999b). Stands vary considerably in appearance and composition, both elevationally and geographically. Juniper tends to be more abundant at the warmer/drier lower elevations, pinyon tends to be more abundant at the higher elevations, and the two species share dominance within a broad middle-elevation zone (Woodin and Lindsey 1954).

The effect of a fire on a stand is largely dependent on the tree height and density, fine fuel load on the ground, weather conditions, and season (Dwyer and Pieper 1967, Wright et al. 1979). Some large trees may survive unless the fire gets into the crown due to heavy fuel loads in the understory or extreme fire conditions.

There are many insects, pathogens, and plant parasites that attack pinyon and juniper trees (Meeuwig and Bassett 1983, Gottfried et al. 1995, Rogers 1995, Weber et al. 1999). For pinyon and juniper, there are at least seven insects, plus blackstain root-rot (Leptographium wageneri) and mistletoes Phoradendron juniperinum and Arceuthobium divaricatum. Both mistletoes reduce vigor and cause occasional dieback but rarely cause mortality (Meeuwig and Bassett 1983). The insects are normally present in these woodland stands, and during drought-induced water stress periods, outbreaks may cause local to regional mortality (Wilson and Tkacz 1992, Gottfried et al. 1995, Rogers 1995). Most insect-related pinyon mortality in the West is caused by pinyon ips beetle (Ips confusus) (Rogers 1993). Pinyons cannot repel pinyon ips beetles when weakened by drought and many are killed.