DYNAMICS OF THE SPRUCE-FIR FORESTS ON THE PINALENO MOUNTAINS, GRAHAM CO ARIZONA

Engelmann spruce (Picea engelmannii Parry)-corkbark fir (Abies lasiocarpa var. arizonica (Merriam) Lemmon) forests in southeastern Arizona are found only in the "sky island" of the Pinaleno Mountains at elevations > 2,800 m. They cover limited area but many stands are old-growth. Recovery to old-growth status after disturbance requires > 300 years for high-elevation sites on gently sloping terrain and follows a sequence of: 1) spruce colonization; 2) reduction in further recruitment of all species; and 3) abundant recruitment of corkbark fir and spruce 80 to 150 years after initial colonization. On steeper, lower elevation sites, spruce or Douglas fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) is the colonizing species. Stand development is slower in this zone, and corkbark fir does not establish until 150 to 250 years after initial colonization.