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, Williamson's Sapsucker, Pygmy Nuthatch, Western Bluebird, and Chipping Sparrow.
Ponderosa pine forests support a rich avifauna, in part a reflection of the prevalence of Gambel
oak in many ponderosa stands. Oak adds structure 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. It was the first species extensively harvested in the 1800s, when it was cut for railroad
ties, mining timbers, firewood, and construction lumber. It remains a favored timber type for
commercial logging and residential firewood collecting. Much of the old-growth ponderosa has
been lost due to logging; the structure of many of the old-growth stands that remain has 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: Four species are identified as high priority in Ponderosa pine habitats
in Physiographic Area 87: Band-tailed Pigeon, Mexican Spotted Owl, Western Bluebird, and Grace's Warbler.