Ponderosa pine can exist as one component of a mixed forest, particularly in combination with Douglas-fir, or as a pure forest type. The typical surface cover in a ponderosa pine forest is a mixture of grass, forbs and shrubs. This forest community generally exists in areas with annual rainfall of 25 inches or less. Extensive pure stands of this forest type are found in the southwestern United States, central Washington and Oregon, southern Idaho and the Black Hills of South Dakota and Wyoming.
For approximately the first five years of their life cycle, ponderosa pine seedlings must compete strenuously with grass cover for survival and are very susceptible to fire. But, beginning in the fifth year or sixth year of its life, the tree begins to develop thick bark and deep roots and sheds its lower limbs. These factors increase its ability to withstand fire and decrease the possibility of a fire climbing to the crown. Furthermore, a thick bed of needles is deposited on the ground, suppressing grasses in the vicinity, thereby controlling the type of fuel available for burning and the type of fire that the tree may need to endure in the future.