Physiognomy and Structure: Vegetation included in this alliance has a moderately dense to dense evergreen tree canopy (35-100% cover), 5-20 m tall, dominated by needle-leaved evergreen trees. Often there are tall- and short-shrub layers dominated by broad-leaved evergreen species with broad-leaved deciduous and needle-leaved species present ranging from 0.5-5 m tall. The herbaceous layer is typically sparse and dominated by perennial graminoids, with annual forbs and grasses present seasonally.

Floristics: This alliance has a moderately dense to dense (>50% cover) tree canopy dominated by the evergreen conifer Hesperocyparis arizonica (= Cupressus arizonica). The broad-leaved tree Quercus hypoleucoides codominates some stands. Other trees are often present to codominant, including conifers Juniperus deppeana, Juniperus monosperma, Pinus edulis, and Pinus monophylla (= Pinus fallax), and evergreen oaks such as Quercus arizonica, Quercus palmeri, and Quercus oblongifolia. The shrub layer is dense and diverse often with over 12 species present. Quercus turbinella, a deciduous broad-leaved shrub, is the most important and a diagnostic species. Other common shrubs and rosette stem succulents include Arctostaphylos pungens, Ceanothus fendleri, Cercocarpus montanus, Fendlera rupicola, Fraxinus anomala, Garrya wrightii, Nolina microcarpa, Prunus virginiana, and Quercus rugosa. The herbaceous layer is typically sparse (<5% cover) because of shading by the overstory, but may be moderately dense depending on the density of the woody canopies and moisture. It is dominated by diverse graminoids such as Bouteloua curtipendula, Carex geophila, Elymus elymoides (= Sitanion hystrix), Koeleria macrantha, Muhlenbergia longiligula, Muhlenbergia richardsonis, Piptochaetium pringlei (= Stipa pringlei), Poa fendleriana, and Schizachyrium scoparium. Packera neomexicana (= Senecio neomexicanus) and Galium spp. are typical of the sparse forb layer. Carmichael et al. (1978) described stands in the Mazatzal Mountains with average cover of Hesperocyparis arizonica, Quercus turbinella, and 11 other shrubs being 37%, 26% and 10%, respectively, for total average cover of 73%.

Dynamics:  Stands occur on a variety of substrates which indicates that other factors, most likely climatic conditions, restrict the distribution of this alliance. The cool, moist conditions required by Hesperocyparis arizonica are not common in southern Arizona. Few occurrences of this alliance have been documented. Brown (1982a) considers these stands to be relictual. Parker (1980b) thinks Hesperocyparis arizonica is a stable, terminal element of limited environments where it now occurs. Its life history resembles that of a pioneer species with additional characteristics that allow it to persist. A trait that leads to persistence is that Hesperocyparis arizonica is very long-lived. The extrapolated ages of individuals from one stand averaged 317 years with the oldest tree being 456 years (Parker 1980b). Also, known stands tend to be mature with little regeneration, and seedlings are able to germinate and grow in the shade of mature trees. Pioneer traits are that it is a prolific seed-producer (estimated 0.1-1 million seeds per tree) and intolerant of ground litter (Parker 1980b). The two stands with a significant number of seedlings had both been disturbed, one by logging and one by flood. Moist, mineral soil is the ideal seedbed for Hesperocyparis arizonica. Parker (1980b) found the number of seedlings decreases with increased litter layer depth.

Fire appears to be important for Hesperocyparis arizonica stand regeneration. Carmichael et al. (1978) report fire opens Hesperocyparis arizonica seed cones. Although Hesperocyparis arizonica is found in areas that are protected from fire and is a non-sprouter with limited fire adaptation, fire removes accumulations of ground litter that prevent seedling establishment (Parker 1980a, 1980b). Parker (1980b) suggested that fire suppression may have limited reproduction, especially in habitats that do not flood, and that current fire suppression policies be eliminated in areas where Hesperocyparis arizonica occurs.