Ponderosa Pine Forests

General Information

Distribution—Ponderosa pine is the most widely distributed pine in North America, extending from British Columbia, Canada, in the north, to Durango, Mexico, in the south. In the United States, it is found from Nebraska west to the Pacific Coast.

Temperature—Regardless of the location where ponderosa pine grows, average annual temperatures are between 42° and 50° F., and average July and August temperatures range between 62° and 70° F. Ponderosa pine is found at elevations from sea level to about 9,000 feet. Throughout its range, as you move from north to south, the species tends to grow at progressively higher elevations, and it is more restricted to higher elevations in drier climates.

Tree Species—Most of the ponderosa pine forests are at elevations between 5,500 and 8,500 ft on the Mogollon Plateau in Arizona. Although ponderosa pine trees dominate these forests, they often contain Douglas-fir, quaking aspen, and southwestern white pine at high elevations, and alligator juniper (Juniper depeanna) and Colorado pinyon (Pinus edulis) and its singleleaf form (P. edulis var. fallax) at low elevations. Gambel oak (Quercus gambelii) is scattered throughout. Grasses and grasslike plants, forbs, and half-shrubs grow beneath ponderosa pine overstories.

Precipitation—Ponderosa pine is generally found in regions with arid conditions and summer rainfall. For typical areas where ponderosa pine grows in the United States, average annual precipitation varies from 10 to 21 inches and the average precipitation during the growing season (May through August) is from 2 to 6 inches. Also see: water yield and potential increase.

Where ponderosa pine grows in Arizona, 6 inches of the total growing seasonal precipitation of seven inches falls in July and August following the May–June dry period. Summer showers provide little moisture that is useful to young pine seedlings. Total growing season precipitation may mean little to the growth of the trees because of the distribution pattern (small rainfall amounts separated by a period of several days of no rainfall). A young tree seedling must quickly develop its root system to be able to reach the water stored in the soil. Thus, ponderosa pine trees mostly depend upon the water stored in the soil for their growth and survival.

High transpiration rates and soil moisture deficiencies can curtail the growth of plants in ponderosa pine even in forests which receive 20 to 30 inches of annual precipitation. High elevation forests tend to have greater frequencies and amounts of precipitation than low elevation forests; although this can be altered by storm patterns and topography. Usually only a small amount of summer rain is converted into streamflow.

Fifty percent or more of the annual precipitation occurs during the winter season and is the major source of runoff—95 percent of the annual streamflow. Because winter precipitation normally occurs as low intensity rain or snow, and runoff is the product of either low intensity rainfall or snowmelt, erosion potential is energy limited, and the dominant parent materials generally limit the supply of sediment (e.g., heavy clay soil characteristic of volcanic-derived soil) or the transport of the dominant sediment size particles (e.g., coarse textured soils derived from sedimentary and granitic parent materials) unless runoff is substantially concentrated.

Resources and activities—Ponderosa pine forests are a valuable source of water, timber, forage, and recreation. Carrying capacities for livestock and wildlife, which graze these rangelands from late spring to early autumn, are relatively high. A diversity of wildlife species use these forests for cover and food, both seasonally and yearlong.

Soils—Ponderosa pine grows on a variety of soils ranging from volcanic to sedimentary origin. The physical properties of the soil, and thus its moisture-retaining capacity, play an important role in the tree's development, possibly more than the chemistry of the soil.

Studies have shown strong relationships between the vertical growth of ponderosa pine and soil depth. In the Black Hills of South Dakota, soil depth had more influence on tree height than soil parent material. In Montana, pine growth response has been related to soil type, effective soil depth, landform, and moisture availability. Increased water at a site increased plant growth regardless of the soil type and landform. The high water tables associated with springs tend to increase site productivity regardless of the soil type and landform.

Volcanic basalt and cinders are the most common soil parent materials in Arizona (57%), although sedimentary soils (43%) are also found throughout these forests. Topography is characterized by extensive flat, rolling mesas, intermixed with steeper, mountainous terrain, and a diversity of slope and aspect combinations.

Images Available

There are currently over 550 images available in the image database illustrating various aspects and conditions found in ponderosa pine ecosystems in southwestern United States. These can be accessed after getting into the database by using the key words ponderosa pine. Additional key words are available for searching the images in a drop down list within the database.