Ponderosa pine (Pinus ponderosa), also called western yellow pine, is one of the most widely distributed pines in western North America. A major source of timber, ponderosa pine forests are also important as wildlife habitat, for recreational use, and for esthetic values. Within its extensive range, two varieties of the species currently are recognized: Pinus ponderosa var. ponderosa (Pacific ponderosa pine) (typical) and var. scopulorum (Rocky Mountain ponderosa pine). Arizona pine (P. arizonica), sometimes classified as a variety of ponderosa pine, is presently recognized as a separate species.
The range of ponderosa pine extends from southern Canada into Mexico, and from the Plains States of Nebraska and Oklahoma to the Pacific Coast.
Pacific ponderosa pine (var. ponderosa) ranges from latitude 52° N. in the Fraser River drainage of southern British Columbia, south through the mountains of Washington, Oregon, and California, to latitude 33° N. near San Diego. In the northeast part of its range it extends east of the Continental Divide to longitude 110° W. in Montana, and south to the Snake River Plain, in Idaho
Rocky Mountain ponderosa pine (var. scopulorum) extends east of the Continental Divide from latitude 48° N. in north-central Montana, southeasterly into North and South Dakota, eastern Wyoming, and as far east as north-central Nebraska. Within this area, ponderosa pine grows on the discontinuous mountains, plateaus, canyons, and breaks of the plains, with the most extensive stands found in the Black Hills of South Dakota and Wyoming. South of Wyoming, Rocky Mountain ponderosa pine extends south on both sides of the Continental Divide, west to Arizona, and the eastern edge of the Great Basin in Nevada, east to Texas west of the Pecos River, New Mexico, extreme northwestern Oklahoma, Colorado, and northern Mexico. Within this wide range, ponderosa pine is absent from a large area that includes southwestern Montana, western Wyoming, southern Idaho, and part of the Great Basin. A possible explanation for the absence is that the distribution of rainfall during the summer months prevents seedling establishment except at higher elevations, where the species has little tolerance for the shorter growing season.