Description and Ecology: In Colorado, ponderosa pine is found at 1700 to 2700 m (5,600-9,000 ft). It is a very dry and warm forest, with less than 65 cm (25 in) of precipitation annually. Mature ponderosa pine forests on dry sites are open and park-like; mature trees achieve wide separation as they compete for limited soil moisture, and a luxuriant grassy ground cover is maintained by frequent low-intensity fires. On more mesic sites, ponderosa stands are denser, and closed-canopy stands are common. Ponderosa pines are the largest conifers in Colorado, with mature specimens reaching 120 cm (4 ft) dbh and 45 m (150 ft) tall. Gambel oak is a common component of the understory, typically in a shrubby form in central Colorado and reaching tree form in the southwest. Gambel oak is important for insectivorous birds, since it supports higher insect populations than other vegetation types in the region. Other common understory shrubs include mountain mahogany and wax currant. Tree species sometimes found mixed with ponderosa pine are junipers, pinyon pine, aspen, lodgepole pine, and Douglas-fir.

Ponderosa pine distribution at local and landscape scales is influenced by soil moisture and fire. Ponderosa forests are shaped primarily by fire, which affects species composition and forest structure. Ponderosa forests evolved with frequent, low-intensity fires that cleared understory vegetation and other tree species with lower fire tolerance, but left unharmed the large ponderosa pines with their thick bark (Moir et al. 1997). Heavy grazing in the 1800s and early 1900s reduced and made discontinuous the grass fuels that fed the low-intensity ground fires. As a result, fires have become far less frequent and shrubs and saplings have crowded the once open stands. Another natural disturbance agent shaping ponderosa pine forests is the mountain pine beetle, which kills many ponderosa pines.

Importance and Conservation Status: Birds typical of the ponderosa pine forest type include Wild Turkey, Pygmy Nuthatch, Western Bluebird, and Chipping Sparrow. More bird species are found in ponderosa pine forests than any other coniferous forest habitat in Physiographic Area 62. This abundant bird life reflects in part the prevalence of Gambel oak in many ponderosa stands. Oak adds structure, acorns, and prey--insect densities are higher in oak than in nearby conifers.

Their large size and low-elevation distribution make ponderosa pines popular for timber harvesting. They were the first timber species extensively harvested in the 1800s, when they were cut for railroad ties, mining timbers, firewood, and construction lumber. They remain a favored timber type for commercial logging and residential firewood collecting. Much of the old-growth ponderosa has been lost to logging, and the structure of many of the old-growth stands that remain have been compromised by dense growth of young trees. Many of the ponderosa pine snags have also been removed, removing a valuable resource for cavity-nesting bird species.

Priority Species Accounts: Five species are identified as high priority in Ponderosa pine habitats in Physiographic Area 62: Band-tailed Pigeon, Flammulated Owl, Mexican Spotted Owl, Lewis's Woodpecker, and Grace's Warbler.