Physiognomy and Structure: No Data Available

Floristics: This forest association is dominated in the tree canopy by the needle-leaved evergreen Hesperocyparis arizonica (= Cupressus arizonica). Several other conifers may be common, including Juniperus osteosperma, Pinus edulis (= var. edulis), or Pinus monophylla (= Pinus edulis var. fallax). Total tree canopy cover is over 50%. The shrub layer is dense and very diverse, with up to 12 species occurring. Quercus turbinella, a broad-leaved evergreen shrub, is the most important and diagnostic species; other shrubs may include the low, evergreens Arctostaphylos pungens and Arctostaphylos pringlei; and the taller evergreens Quercus chrysolepis, Rhus ovata, Cercocarpus montanus, and Purshia mexicana (= Cowania mexicana). The herbaceous layer is typically sparse, with <5% cover, due to the dominance and shading of the tree and shrub layers.

Dynamics:  Mosaic patterns of different aged stands of uniform height and density are due to the patchy nature of surface fires which typically kill some but not all trees. Seedlings and saplings (diameters <10 cm [4 inches]) have almost no resistance to even low-intensity surface fires. Surface fire may kill all seeds in cones on the ground (Parker 1980a). Larger trees also exhibit little fire resistance. Crown fires may actually open cones on the tree, killing a portion of the seeds in the cone.

For Arizona cypress, too frequent fires can wipe out a grove, yet fire is needed sometime in its history to produce conditions for reproduction. Moir (1982) suggested that low-intensity surface fires with a frequency of 50 to 60 years serve to thin out Mexican pinyon thickets which could eventually exclude Arizona cypress. Fire frequencies exceeding 80 years may allow fuel buildup and produce a shift in dominance patterns from those species that are maintained by recurrent fire (Swetnam et al. 1989).