Pinus ponderosa

The taxonomy of the ponderosa pine complex is not completely resolved (Flora of North America 1993). FNA (vol. 2, 1993) includes Pinus arizonica (= P. ponderosa var. arizonica) as a variety of P. ponderosa. There are morphological and distributional overlaps, and disagreement regarding the geographical boundaries of varieties of ponderosa pine. Hybridization also occurs between all three varieties. (Howard 2003).

Widely distributed in mountainous regions from British Columbia far into Mexico (including northern Sonora and Chihuahua) and from California to Nebraska, in many places forming great forests. Grows in rather open forests, but forms fairly dense stands on the higher slopes. Harvested for timber, particularly in northern Sonora and Chihuahua where it occurs between 6000 and 8000 ft alt. As a native, long-lived tree species, few populations may be showing some decline, especially from increased severity of fire events and overharvesting in some areas, however the species is still considered common and wide-ranging.

Ponderosa pine is the most widely distributed pine species in North America, ranging north-south from southern British Columbia to central Mexico and east-west from central Nebraska to the west coast (Howard 2003).

Dwarf mistletoe (Arceuthobium spp.) is a serious disease of ponderosa pine with infection rates up to 33% in some areas (Howard 2003). Dwarf mistletoe alters tree form, suppresses growth, and reduces volume and overall wood quality of its host (Epp & Tardif 2004). Mountain pine beetles (Dendroctonus ssp.) and bark beetles (Ips spp.) are also serious pests of ponderosa pine with regular infestations occurring over centuries of time. However, beetle epidemics combined with environmental conditions such as prolonged drought has resulted in increased pine mortality in many regions (Howard 2003). Older age classes of ponderosa pine are being lost from stands (Howard 2003), however this doesn't represent a loss in genetic diversity in tree species (Hamrick 2004).