Ponderosa pine forest

Ponderosa pine forest is the largest western forest type in the United States. Since ponderosa pine has a rather wide range of adaptability and can dominate some of the less mesic true forest sites, it occupies low mountains and foothills in many places; yet in mixtures with other species, it is found at moderate elevations. ==Climate==

Ponderosa pine forest occurs when the average mean temperature is between and the July/August mean temperature is . The length of the frost-free season at any location in the ecosystem depends largely upon the latitude and elevation. In general, in much of the northern area the frost-free period is 120 days, whereas in many foothill areas and in parts of the Sierra Nevada and the Gila Wilderness in Arizona, it can be 240 days. Annual precipitation is about in the more pure pine areas, but where there are combinations of pine and other conifers at moderate elevations, the precipitation can total . In the far western sector, only 25 percent of this moisture falls in the warmest months. In the Northern Rocky Mountains, 40-50 percent of the precipitation occurs in the warmest months. In the middle to southern Rockies, 66 to 75 percent occurs in the warmest months. In the southern areas and those at low elevations, precipitation during the frost-free season is only 20 percent of the evaporation potential. In northern areas precipitation during the growing season may be as high as 40 percent of the evaporation potential. ==Vegetation==

'' can aggressively compete with ponderosa pine seedlings Ponderosa pine forest can occur in different types of ecological site. Each of these sites can be characterized by its potential vegetation type (PVT) after succession reaches equilibrium or climax community. In the southern and extreme eastern portion of the range, ponderosa pine grows primarily on ponderosa pine PVTs. On these settings, quaking aspen is the most frequent early-seral tree species. Mid-seral shrubs include Rocky Mountain maple which readily survives disturbances and is joined by late-seral species such as huckleberry (Vaccinium spp.) and false huckleberry (Menziesia ferruginea). The latter readily survives disturbances but is an aggressive colonizer. Probably one of the greatest competitors and survivors after disturbance of any ground-level species occurring with ponderosa pine is pinegrass. This ground-level vegetation can play critical roles in forests such as providing wildlife habitat, stabilizing soil, and capturing nutrients after disturbance. For example, fireweed (Chamerion angustifolium) rapidly regenerates after fire and captures and recycles nitrogen. Because of the range of species that can occur with ponderosa pine and their wide range of tolerance (e.g., shade, competition, fire) along with how they interact with disturbances a plethora of vegetative compositions and structures can occur within ponderosa pine forests arranged and interspersed in a variety of mosaics. The impact of logging and ecological dynamics can cause some problems in maintaining good delineation of the ponderosa pine ecosystem. This ecosystem is idealized as open and parklike with an excellent ground cover of grasses, sedges, and forbs or with an understory of shrubs of low to medium height. In perhaps 60 percent of the area, the idealized open character of the ponderosa pine ecosystem has changed to that of a dense and growth-retarded stand, particularly in the Pacific Northwest. ==Fauna==

is only found in mature ponderosa pine forest. The large mammals that inhabit the ponderosa pine ecosystem are the Rocky Mountain elk, mule deer, mountain lion, and coyote. Smaller animals include the bushy-tailed woodrat, white-footed mouse, bobcat, rock squirrel, cottontail rabbit, porcupine, and golden-mantled ground squirrel. The Kaibab squirrel is rare and endemic to this ecosystem on Arizona's Kaibab Plateau on the north rim of the Grand Canyon. Bird species that live in the ponderosa pine ecosystem include the pygmy nuthatch, Steller's jay, sharp-shinned hawk, Rocky Mountain nuthatch, mountain chickadee, Cassin's finch, redshafted flicker, red-backed junco, northern goshawk, and western red-tailed hawk. Birds that are common during the summer include the western bluebird, Audubon's warbler, Williamson's sapsucker, western chipping sparrow, horned owl, and band-tailed pigeon. ==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. Along the western edge of the Columbia Plateau and the east slope of the Cascade Mountains, common soil types are mollisols, inceptisols, entisols, and aridisols. In northern and eastern California, ponderosa pine stands are associated with ultisols. In the Okanogan Highlands at the northern edge of the Columbia Plateau and in much of the Northern Rocky Mountains, pine and the related forest types occur on inceptisols; the soils of the rest of these areas are largely alfisols and entisols. In the Blue and Wallowa Mountains of eastern Oregon, pine stands occupy mollisols. In the Middle and Southern Rocky Mountains, pines and associates are on mollisols, aridisols, entisols, and alfisols. Pine stands in the Gila Mountains are largely on mollisols. The small stands of pine in the Great Basin are on aridisols. ==Disturbances==

Wildfire , Arizona Before successful fire exclusion, temperature and precipitation patterns combined with natural and human ignitions allowed fires to burn the dry ponderosa pine forests at relatively frequent (e.g., < 40 years) intervals, Cultural burning by Native Americans augmented and even dominated burning in several locations. In addition to ponderosa pine being damaged by insects, dense stands of Douglas-fir and grand fir or white fir that developed on many settings arevery susceptible to both defoliators and root diseases. ==See also==