This Species Review covers two varieties of ponderosa pine, Pinus ponderosa var. benthamiana and P. p. var. ponderosa. 'Ponderosa pine' refers to both varieties. Ponderosa pine adapted to dry environments but occupies a wide variety of sites. It dominates or codominates low-elevation, dry forests and tends to form savannas in which there are few or no other tree species on xeric sites. I t grows with other overstory trees on more mesic sites and at midelevations. Ponderosa pine regenerates most successfully after disturbances that open the canopy and expose bare mineral soil. Fire is the primary agent creating these conditions. Seed production varies within and among populations and between years. Wind and animals disperse the seeds. Few seeds actually establish. For those that do, growth is most favorable on open sites with light shade, such as sites that have been burned or thinned. Ponderosa pine is shade intolerant. It is a successionally stable or climax species on low-elevation, dry sites and seral on more mesic and midelevation sites. Under fire exclusion, many contemporary ponderosa pine forests have denser stand structures than the forests had historically. Live and dead fuels have increased as shade-tolerant species replace ponderosa pine successionally. Ponderosa pine is adapted to low- and moderate-severity surface fires. Effects of fire generally vary with tree age and fire severity. Low-severity surface fire usually kills ponderosa pine seedlings, while saplings and pole-sized trees generally survive. Ponderosa pines over 10 to 12 feet (3-4 m) tall usually survive moderate-severity surface fires. Fall fires generally cause more injury and mortality than spring fires. Postfire mortality may be delayed for several years and may be exacerbated by drought and bark beetle attacks. Ponderosa pine establishes from wind- and wildlife-dispersed seed in open patches where fire killed overstory trees. If open patches are too big, distance from off-site parent trees limits seed dispersal into burn interiors. Regeneration can be poor on sites that experience stand-replacement fire, especially when fires are large. Historically, fire maintained ponderosa pine as a dominant throughout its range. Before European settlement around the mid-1850s, low-elevation, dry ponderosa pine and dry ponderosa pine-Douglas-fir forests had mostly frequent, low- and moderate-severity surface fires and mixed-severity fires. Historical fire intervals in ponderosa pine forests were generally short-averaging about 10 years-but ranged from 1 to 80 years across the ranges of Pinus ponderosa var. benthamiana and P. p. var. ponderosa. Fires became infrequent when fire exclusion became effective in the 1930s. Ponderosa pine ecosystems historically experienced both small and large fires, but large patches of severe fire were uncommon. In recent decades, the proportion of area that has burned at high severity has increased in ponderosa pine forests across ponderosa pine’s range. This has been attributed primarily to successional advancement under fire exclusion and climate change. Frequent low- to moderate-severity fires can reduce fuel loads and kill young conifers in the understory; reduce mortality of mature ponderosa pines from subsequent fires; help restore reference-condition forest structure and composition; promote regeneration of shade-intolerant conifers; and increase resilience of dry forest ecosystems.