Physiognomy and Structure: These are widely spaced woodland stands of needle-leaved evergreen trees 10-30 m in height. Associated trees are primarily needle-leaved evergreen species. The understory may consist of a depauperate shrub layer with cover typically <5%. and a dense herbaceous understory predominantly dominated by graminoids.

Floristics: This alliance includes woodlands dominated by Pinus ponderosa. Structurally, these are savannas with large, open growth-form Pinus ponderosa trees (generally) as the only canopy dominant. Average tree canopy cover ranges from 10-50%. Other conifers, including Juniperus spp., Pinus discolor, Pinus edulis, and Pseudotsuga menziesii, may be present at low cover. The diagnostic feature of this alliance is the depauperate shrub layer with cover typically <5% and moderate to dense herbaceous understory predominantly dominated by fire-resistant grasses. Shrubs which may occur at low cover include Artemisia tridentata, Brickellia californica, Ceanothus fendleri, Ceanothus fendleri, Cercocarpus montanus, Chrysothamnus viscidiflorus, Ericameria nauseosa, Fallugia paradoxa, Mahonia spp., Purshia tridentata, Quercus gambelii, Quercus grisea, Rhus trilobata, Tetradymia canescens, and Yucca baccata. The herbaceous layer is dense and composed of fire-resistant graminoids. Dominant species may include Andropogon gerardii, Bouteloua gracilis, Festuca arizonica, Muhlenbergia montana, Muhlenbergia straminea (= Muhlenbergia virescens), and Schizachyrium scoparium. Other graminoid associates may include Achnatherum lobatum (= Stipa lobata), Andropogon gerardii, Aristida spp., Bothriochloa barbinodis (= var. barbinodis), Bouteloua curtipendula, Bouteloua hirsuta, Carex geophila, Carex rossii, Elymus elymoides, Hesperostipa comata, Koeleria macrantha, Piptochaetium fimbriatum, and Piptochaetium pringlei. An assortment of forbs may occur, but cover is low relative to graminoids. Common associates may include Ageratina rothrockii (= Eupatorium rothrockii), Allium cernuum, Antennaria spp., Artemisia ludoviciana, Campanula rotundifolia, Chaetopappa ericoides, Chaetopappa ericoides, Erigeron spp., Lotus wrightii, Oxytropis lambertii, Packera neomexicana, Penstemon spp., and Silene laciniata.

Dynamics:  Pinus ponderosa is a drought-resistant, shade-intolerant conifer which usually occurs at lower treeline in the major ranges of the western United States. Historically, surface fires and drought were influential in maintaining open-canopy conditions in these woodlands. With settlement and subsequent fire suppression, stands have become more dense. Presently, many stands contain understories of more shade-tolerant species, such as Pseudotsuga menziesii and/or Abies spp., as well as younger cohorts of Pinus ponderosa. These altered stand structures have affected fuel loads and altered fire regimes. Presettlement fires were frequent (5- to 15-year return intervals) with low-intensity surface fires triggered by lightning strikes or deliberately set by Native Americans. With fire suppression and increased fuel loads, fires are now less frequent and often become intense crown fires which can kill mature Pinus ponderosa. Establishment is erratic and believed to be linked to periods of adequate soil moisture and good seed crops, as well as fire frequencies which allow seedlings to reach sapling size. Longer fire-return intervals have resulted in many stands having dense subcanopies of overstocked and unhealthy young Pinus ponderosa.