Index of Species Information

SPECIES:  Pinus ponderosa var. ponderosa

Introductory

SPECIES: Pinus ponderosa var. ponderosa
AUTHORSHIP AND CITATION : Habeck, R. J. 1992. Pinus ponderosa var. ponderosa. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].
ABBREVIATION : PINPONP PINPON SYNONYMS : NO-ENTRY SCS PLANT CODE : PIPO COMMON NAMES : Pacific ponderosa pine ponderosa pine western yellow pine bull pine TAXONOMY : The currently accepted scientific name of Pacific ponderosa pine is Pinus ponderosa var. ponderosa Dougl. [28]. Three varieties of ponderosa pine are currently recognized and are distinguished by morphological variations and geographical location [7,48]: var. arizonica (Engelm.) Shaw - Arizona pine. (classified as a separate species, P. arizonica Engelm.), by some authorities). Occurs in the mountains of extreme southwest New Mexico, southeast Arizona, and northern Mexico. Has shorter cones and narrower cone scale prickles. Usually has five-needle fascicles. var. ponderosa - Pacific ponderosa pine. Extends from the mountains of southern California northward along the Sierra Nevada-Cascade Range to southern British Columbia. Usually has three-needle fascicles. var. scopulorum (Engelm.) - Interior ponderosa pine. Extends from west-central Montana, southward through the mountains, plains, and basins of Colorado, Arizona, and New Mexico. Has a moderate to high proportion of two-needle fascicles. LIFE FORM : Tree FEDERAL LEGAL STATUS : No special status OTHER STATUS : NO-ENTRY

DISTRIBUTION AND OCCURRENCE

SPECIES: Pinus ponderosa var. ponderosa
GENERAL DISTRIBUTION : Pacific ponderosa pine ranges from latitude 52 degrees N in the Fraser River Drainage of southern British Columbia south through the mountains of Washington, Oregon, and California to latitude 33 degrees N near San Diego.  In the northeastern part of its range it extends east of the Continental Divide to longitude 110 degrees W in Montana and south to the Snake River Plain in Idaho [48]. ECOSYSTEMS :    FRES20  Douglas-fir    FRES21  Ponderosa pine    FRES22  Western white pine    FRES25  Larch    FRES26  Lodgepole pine    FRES28  Western hardwoods    FRES34  Chaparral - mountain shrub    FRES36  Mountain grasslands STATES :      CA  HI  ID  MT  NV  OR  WA  BC BLM PHYSIOGRAPHIC REGIONS :    2  Cascade Mountains    3  Southern Pacific Border    4  Sierra Mountains    5  Columbia Plateau    7  Lower Basin and Range    8  Northern Rocky Mountains KUCHLER PLANT ASSOCIATIONS :    K002  Cedar - hemlock - Douglas-fir forest    K005  Mixed conifer forest    K010  Ponderosa shrub forest    K011  Western ponderosa forest    K012  Douglas-fir forest    K013  Cedar - hemlock - pine forest    K034  Montane Chaparral SAF COVER TYPES :    210  Interior Douglas-fir    211  White fir    212  Western white pine    213  Grand fir    215  Western white pine    217  Aspen    218  Lodgepole pine    228  Western redcedar    229  Pacific Douglas-fir    231  Port-Orford-cedar    233  Oregon white oak    234  Douglas-fir - tanoak - Pacific madrone    243  Sierra Nevada mixed conifer    244  Pacific ponderosa pine - Douglas-fir    245  Pacific ponderosa pine    246  California black oak    247  Jeffrey pine    248  Knobcone pine    249  Canyon live oak    250  Blue oak - Digger pine SRM (RANGELAND) COVER TYPES : NO-ENTRY HABITAT TYPES AND PLANT COMMUNITIES : Pacific ponderosa pine forms climax stands that border grasslands and is also a common seral tree on many other forested sites [63].  Being drought tolerant, it is usually occupies the transition zone between grassland and forest.  Climax stands are characteristically warm and dry, and occupy lower elevations throughout their range.  Key understory associates in climax stands typically include grasses such as bluebunch wheatgrass (Pseudoroegneria spicata) and Idaho fescue (Festuca idahoensis), and shrubs such as bitterbrush (Purshia tridentata) and common snowberry (Symphoricarpos albus).  At higher elevations, Pacific ponderosa pine is seral to trees that are more shade tolerant and moisture demanding.  In the Pacific Northwest this generally includes Douglas-fir (Pseudotsuga menziesii), grand fir (Abies grandis), and white fir (A. concolor) [8,18,49,63]. Publications listing Pacific ponderosa pine as an indicator or dominant species in habitat types (hts), community types (cts), and plant associations (pas) are as follows:  Area            Classification                  Authority  ----            --------------           -------------------------   CA              forest (pas)             Atzet & Wheeler 1984   CA              forest (cts)             Erhard  1979   CA              forest (hts)             Horton  1960   ID              forest (pas)             Schlatterer 1972   ID              forest (cts)             Tuhy & Jensen 1982 c ID              forest (hts)             Steele & others 1981 n ID              forest (hts)             Cooper & others 1991   MT              forest (hts)             Pfister & others 1977   OR              forest (pas)             Kovalchik 1987   OR              forest (pas)             Hopkins 1979b   OR              forest (pas)             Hopkins & Kovalchik 1983   OR              forest (pas)             Johnson & Simon 1987 c OR              forest (pas)             Volland 1985 e OR  se WA       forest (cts)             Hall 1973   WA              forest (pas)             Williams & Lillybridge 1983 e WA  n ID        forest (hts)             Daubenmire & Daubenmire 1968

MANAGEMENT CONSIDERATIONS

SPECIES: Pinus ponderosa var. ponderosa
WOOD PRODUCTS VALUE : Pacific ponderosa pine is a valuable lumber species in the Inland West, with 1986 sales exceeding 1.4 billion dollars in wholesale value [4]. Old-growth Pacific ponderosa pine produces clear, high-grade lumber, although young trees are typically limby because natural pruning develops slowly.  An average clear length of only 11.5 feet (3.5 m) was recorded in 250 year-old stands in central Idaho [48].  Consumption of Pacific ponderosa pine wood products is primarily limited to the United States, with some export to Canada.  A large percentage of small, low-grade trees are processed into dimensional lumber and other products for the construction market.  High-grade lumber is an important raw material for molding, mill work, cabinets, doors, and windows [4]. IMPORTANCE TO LIVESTOCK AND WILDLIFE : Food:  Pacific ponderosa pine needles, cones, buds, pollen, twigs, seeds, and associated fungi and insects provide food for many species of birds and mammals [13].  Small mammals that eat stems and roots include deer mice, chipmunks, shrews, voles, and tree and ground squirrels. Large browse mammals include elk, deer, porcupines, hares, rabbits, cattle, sheep, and occasionally horses, goats, and feral hogs [6,13,29,41].  Many bird species eat Pacific ponderosa pine seeds. These include the junco, Cassin's finch, pine siskin, evening grosbeak, varied thrush, Clark's nutcracker, and a host of sparrows, chickadees, and other passerines [13,21,49]. Shelter:  At each morphological stage, Pacific ponderosa pine provides numerous species of birds and mammals with shelter.  As seedlings they provide low ground cover for small birds and mammals.  Upon reaching pole size, stands provide good windbreaks and thickets important as hiding cover for larger mammals such as elk and deer.  Mature trees and standing snags house arboreal species, while fallen logs and stumps provide many cavity-dwelling species with adequate shelter [27,49]. PALATABILITY : In Montana, Pacific ponderosa pine is considered low in palatability for cattle, horses, and sheep [11].  Elk in northwestern Montana also find it unpalatable.  Elk, along with deer and bighorn sheep, occasionally browse on stems and bark during times of food or water scarcity [19,74]. NUTRITIONAL VALUE : Nutrient means for Pacific ponderosa pine structural components from Lubrecht Experimental Forest, western Montana, are as follows [61]:         Green Needles        Twigs           Wood       Sound Wood                  (1 Year)      (0.64-2.5 cm)*  (2.5-7.6 cm)   ( >7.6 cm) ------------------------------------------------------------------------ Ca         3,069.0**        2,029.0        1,013.0         659.0 Cu             5.4              6.3            7.0           4.8 Fe           118.0             59.6           23.3          28.5 K          4,952.0          1,627.0          741.0         395.0 Mg         1,036.0            627.0          336.0         250.0 Mn           205.0             75.0           65.0          62.2 N         10,455.0          2,857.0        1,012.0         692.0 Na            32.0             31.0           22.8          31.4 P          1,329.0            367.0          200.0         387.0 Zn            34.3             27.1           16.9           5.8 Percent    ash          3.4             0.99           0.78          0.33  * Measurement in diameter. ** All values are express in micrograms per gram. COVER VALUE : Pacific ponderosa pine is important in providing wildlife cover. Species using this tree for cover include the bald eagle, wild turkey, and band-tailed pigeon for roosts; and squirrels, hawks, and owls for nest trees.  Primary and secondary cavity-nesting birds such as the acorn woodpecker and mountain chickadee use both live and dead pine trees.  Pacific ponderosa pine provides thermal and escape cover for mule deer and elk.  Fallen logs and stumps are used as cover by cottontails, small rodents, and reptiles [27,49]. VALUE FOR REHABILITATION OF DISTURBED SITES : Pacific ponderosa pine is widely used for soil stabilization and watershed protection in the Rocky Mountain region [67].  Bareroot stock is used occasionally for planting on mine-spoils in the West [72]. OTHER USES AND VALUES : Pacific ponderosa pine stands offer year-round recreation and aesthetic scenery [48].  Native Americans in the Pacific Northwest used the inner cambial layer as food.  They also converted the resin into medicinal salve for rheumatism, backaches, and dandruff [24,41]. OTHER MANAGEMENT CONSIDERATIONS : Insects:  Approximately 200 insect species may affect Pacific ponderosa pine from its cone stage to maturity [58].  The effects of insect damage are:  decreased seed and seedling production, reforestation failures or delays, and reduction of potential timber productivity [13,58].  Several insect species destroy seeds before they germinate, the most damaging being the ponderosa pine cone beetle (Conophthorus ponderosae) and the pine seed chalcid (Megastigmus albifrons).  Seedlings and saplings are deformed by tip moths (Rhyacionia bushnelli), shoot borers (Eucosma sonomana), and budworms (Choristoneura lambertiana).  Two major lepidopteran pests, the pine butterfly (Neophasia menapia) and pandora moth (Coloradia pandora), severely defoliate their hosts causing growth reductions.  Extensive mortality in defoliated stands usually results from simultaneous infestations by bark beetles.  Bark beetles, primarily of the genus Dendroctonus and Ips, kill thousands of pines annually and are the major mortality factor in commercial sawtimber stands.  These insects can be managed through the use of insecticides, pheromones, or by stand improvement techniques [58]. Disease:  Pacific ponderosa pine is affected by many diseases. Parasites, root diseases, rusts, trunk decays, and needle and twig blights cause significant damage.  Dwarf mistletoe (Arceuthobium campylopodum) causes the most damage.  A major root disease of pine is caused by white stringy root rot (Fomes annosus) and is often found in concert with bark beetle infestations.  Western gall rust (Endocronartium harknessii), limb rust (Peridermium filamentosum), and comandra blister rust (Cronartium comandrae) cause damage only in localized areas.  Various silvicultural treatments can minimize damage caused by dwarf mistletoe.  Clear-cutting is used only if regeneration is not a problem.  The pruning of branches and witches brooms, fertilization, watering, and the planting of nonsusceptible species also aid in combating dwarf mistletoe.  Spraying with the growth regulator Ethephon also temporarily limits mistletoe spread [25]. Chemical control:  Limiting the invasion of Pacific ponderosa pine onto valuable grazing land or for stand management has been achieved through the use of chemical control [15].  Tordon 101 and 22K applied in July is effective [34], although Cacodylic acid has been shown to consistently kill this tree [47].

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Pinus ponderosa var. ponderosa
GENERAL BOTANICAL CHARACTERISTICS : Pacific ponderosa pine has the potential for achieving large dimensions. Stems of 103.5 inches (263 cm) in d.b.h. and 232 feet (70.7 m) in height have been recorded.  Diameters at breast height of 30 to 50 inches (76-127 cm) and heights of 90 to 130 feet (27.4-39.6 m) are common throughout its range [5].  Trees often reach ages of 300 to 600 years [48].  Needles are typically in bundles of three.  They are 5 to 10 inches (12.5-25.0 cm) long and form tufts at the end of each branch. Cones are oval and 3 to 6 inches (7.5-15.0 cm) long.  The bole is typically straight and at maturity is clear of lower branches.  The bark of mature trees is composed of broad, irregular scaly-plates that fit together like jigsaw puzzle pieces.  The crown is conical and composed of stout branches [38,48]. RAUNKIAER LIFE FORM :       Phanerophyte REGENERATION PROCESSES : Pacific ponderosa pine reproduces sexually.  It does not regenerate naturally by vegetative methods.  It can be propagated by rooting and grafting, but success decreases rapidly when scions are taken from trees older than 5 years [48]. Seedling development:  Successful natural regeneration of Pacific ponderosa pine is accomplished by a combination of heavy seed crops, favorable weather during the growing season, soil texture, low competition, and exposed mineral seedbeds [26,39].  Moisture-stress reduces seed germination as well as initial seedling survival and development.  Pacific ponderosa pine has the capacity for root growth in relatively dry soil.  Nursery stock removed in January from California had appreciable root elongation even when planted in soil with very low water potential.  Shrub competition reduces the height and diameter growth of seedlings planted in northern California and Oregon.  On the western slopes of the Sierra Nevada, growth starts noticeably later with each 2,000 foot (610 m) increase in elevation.  Rates of height and radial growth do not vary with elevation during the growing season [48]. Seed production and dissemination:  Seed production varies with geographic distribution.  There are generally 6,900 to 23,000 clean ponderosa pine seed per pound (6,210-20,700 per kg) [36].  In California west of the Sierra Nevada, medium seed crops are borne on an average of every 2 to 3 years.  The average interval between heavy cone crops is 8 years; in the Pacific Northwest it is every 4 to 5 years.  Twenty-three years of data show Pacific ponderosa pine to be a poor seeder in western Montana.  It bears cones as early as 7 years and continues to produce good cone crops up to at least 350 years.  Optimum seed viability is produced by trees 60 to 160 years old.  In California, trees greater than 25 inches (64 cm) d.b.h. were the most dependable seed producers. Recommended cold stratification period is 30 to 60 days for stored seeds at 33 to 41 degrees F (1-5 deg C).  Wind does not disseminate Pacific ponderosa pine seeds beyond about 100 feet (31 m) from the seed source. In central Oregon, the amount of seeds reaching the ground at 132 feet (40 m) into a clear-cut was only 22 percent that of those measured at the timber's edge.  At 528 feet (161 m) it was only 8 percent.  Nearly all seeds are disseminated by early November.  In a good seed year, as many as 345,080 seeds per acre (852,050 seeds per hectare) may reach the ground [48,79].  Clark's nutcrackers cache Pacific ponderosa pine seeds.  Unretrieved seeds in Clark's nutcracker caches may have a better change of establishment than wind-dispersed seed [83,84]. Seedling mortality and predation:  Many variables are responsible for seedling mortality.  Seedlings younger than 36 days old are more susceptible to minimum night temperatures cooler than 23 degrees F (-5 deg C) than are lodgepole pine (Pinus contorta) seedlings.  During winters with little snowcover, 1- and 2-year-old seedlings may suffer damage and frost kill.  Also, 1- to 3-month-old seedlings are killed by stem temperatures of 130 degrees F (54 deg C) and higher.  Pacific ponderosa pine seeds are consumed by a number of birds and small mammals.  Squirrels and porcupines clip many of the cone-bearing twigs, hence destroying flowers and conelets.  Rabbits and hares injure or kill many seedlings by nibbling young stems, while pocket gophers may decimate an entire population of seedlings.  Repeated browsing by deer may stunt seedling growth for up to 50 years [13].  Livestock also damage seedlings and saplings by trampling, bedding, and browsing.  Many species of insects and disease affect Pacific ponderosa pine.  See MANAGEMENT CONSIDERATIONS for further discussion [48]. SITE CHARACTERISTICS : Throughout its range, Pacific ponderosa pine is dependent upon several site variables such as soils, elevation, and climate [68].  Soil moisture is the variable most often limiting growth, especially in the summer months when rainfall is deficient [48]. Climate:  Pacific ponderosa pine is typically found on warm, dry sites. The climate is characterized by a short growing season and minimal summer precipitation.  The mean annual precipitation ranges from 11 to 17 inches (28-43 cm), with summer precipitation averaging 5 to 10 inches (13-25 cm).  Average annual precipitation ranges from about 14 to 30 inches (35-75 cm) on Pacific ponderosa pine sites in Oregon and Washington, and is typically in the form of snow [18].  The western slope of California's northern Sierra Nevada may be the wettest area supporting Pacific ponderosa pine, with an annual rainfall reaching 69 inches (173 cm).  In contrast, this species occupies areas in California where extreme rainfall deficiencies occur [July and August precipitation about 1 inch (2.5 cm) or less] [48]. Soil and topography:  Pacific ponderosa pine occurs on a wide variety of soils ranging from glacial till, glacio-fluvial sand and gravel, dune, basaltic rubble, colluvium, to deep loess or volcanic ash.  This pine develops best on wet, deep, sandy gravel and clay loams with pH between 6.0 and 7.0.  Throughout its extensive range, however, it will most often be found on a variety of loams, loamy sand, and gravel; with a pH from 4.9 to 9.1 [68,74].  Many studies have shown better survival and growth rates on coarse-textured clayey soils where extensive root proliferation is possible [18].  In Oregon, Pacific ponderosa pine soils are typically less than 40 inches (100 cm) deep and formed from loess and basalt colluvium and bedrock materials.  Surface layers have silt loam to silty clay loam textures with greater than 35 percent rock fragments by volume.  Surface rocks usually exceed 10 percent cover [33].  Pacific ponderosa pine has been found on a variety of sites from steep slopes in the plateau region of northern Idaho and Oregon to the flat coastal plains of California [7,48]. Elevation:  Elevational ranges of Pacific ponderosa pine are as follows [68]: State              Mean ft (m)                Range ft (m) -----             -------------        ----------------------------- California        3,242   (988)         348 to 6,520  (106-1,987 m) Oregon (eastern)  5,400 (1,646)       1,800 to 9,000  (549-2,743 m) Oregon (western)  2,800   (853)       2,200 to 3,400  (670-1,036 m) Washington        2,625   (800)         330 to 4,950  (100-1,510 m) Associated forest cover:  Pacific ponderosa pine is associated with a rich variety of tree species.  Only five of these, however, western juniper (Juniperus occidentalis), Rocky Mountain juniper (J. scoparium), quaking aspen (Populus tremuloides), lodgepole pine, and Oregon white oak (Quercus garryana), are common associates in climax stands [18]. Understory associates can be categorized into two groups: a shrub- and forb-rich group and a drier bunchgrass-dominated group.  The climax shrub-dominated undergrowth generally includes ninebark (Physocarpus malvaceus), common snowberry, and bitterbrush.  Seral site shrubs generally include blue huckleberry (Vaccinium globulare) and bearberry (Arctostaphylos uva-ursi) [9,49,63]. SUCCESSIONAL STATUS : Historically, fire has played the greatest role in the successional status of Pacific ponderosa pine.  See FIRE ECOLOGY for further discussion. In many areas of the Pacific Northwest, the first zone above the grasslands is the Pacific ponderosa pine climax.  This tree species is shade intolerant and grows most rapidly in near full sunlight [18,74]. There is a strong tendency for climax pine stands to be even-aged in small groups rather than being truly uneven-aged.  Heavy grazing induces effects opposite those of fire.  Removal of the grass cover by grazing tends to favor shrub communities.  Logging is usually done by a selection-cut method.  Older trees are taken first, leaving younger, more vigorous trees as growing stock.  This method substantially accelerates the successional trend toward a more climax dominant tree species.  Logging also impacts understory species by machine trampling or burial by slash.  Clear-cutting generally results in dominance by understory species present before logging, with invading species playing only a minor role in postlogging succession [18,39]. The successional status of Pacific ponderosa pine can be expressed in terms of its successional role, which ranges from seral to climax depending on specific site conditions.  It plays a climax role on sites toward the extreme limits of its environmental range and becomes increasingly seral with more favorable conditions.  On sites with more favorable moisture, pine encounters greater competition and must establish itself opportunistically.  On moist sites it is usually seral to Douglas-fir and the true firs (mainly grand fir and white fir).  On severe sites it is climax by default because other species cannot establish.  On such sites, establishment is likely to be highly dependent upon the cyclical nature of large seed crops and favorable weather conditions [62]. SEASONAL DEVELOPMENT : In California, Pacific ponderosa pine flowers from April to June; cone ripening and seed dispersal occur from August to September [48].

FIRE ECOLOGY

SPECIES: Pinus ponderosa var. ponderosa
FIRE ECOLOGY OR ADAPTATIONS : Fire is an integral part of the ecology of Pacific ponderosa pine. Studies have shown that prior to 1900, most stands experienced low-severity surface fires at intervals ranging from 1 to 30 years. Fire scars and pollen analysis trace this phenomena back to at least A.D. 1500.  Fire has allowed Pacific ponderosa pine to dominate sites where it is the potential climax as well as sites where it is seral to more shade-tolerant tree species [2,22,26,39]. Pacific ponderosa pine has evolved with a thick bark and open crown structure that allows it to survive most fires.  Mature trees will self-prune, leaving a smooth bole which reduces aerial fire spread. Other fire adaptations include deep roots, high foliar moisture content, insulated bud scales, and medium to light lichen growth [16,17,54]. Seedlings prefer the mineral-soil seedbeds created by fire [42]. Fire also shapes the composition of Pacific ponderosa pine stands.  In the late 1800's stands exhibited open parklike appearances with well-stocked overstories and relatively few understory trees.  Fire suppression, however, has allowed the unnatural buildup of forest fuels which has increased the occurrence of stand-replacing fires.  Over the last 100 years of fire suppression, seral Pacific ponderosa pine stands have been replaced by shade-tolerant climax stands [2,22,26]. POSTFIRE REGENERATION STRATEGY :    Crown-stored residual colonizer; short-viability seed in on-site cones    Off-site colonizer; seed carried by wind; postfire years 1 and 2    Off-site colonizer; seed carried by animals or water; postfire yr 1&2

FIRE EFFECTS

SPECIES: Pinus ponderosa var. ponderosa
IMMEDIATE FIRE EFFECT ON PLANT :
Biscuit Fire. Photo compliment of Wildlandfire.com.
Fire has a wide variety of potential effects on Pacific ponderosa pine. These effects vary according to size, configuration, and density of the stand, in addition to fire severity.  Generally, well-spaced seedlings and saplings are able to withstand low-severity fires, as are pole-sized and mature trees.  Moderate- to high-severity fires, however, will kill trees pole-sized and smaller.  Mature Pacific ponderosa pines have a higher survival rate than younger trees due to their enhanced adaptations to fire [16,39,77]. The principal cause of mortality following fire is crown scorch rather than damage to the cambium or roots.  The size of tree determines its ability to withstand scorch.  A model has been developed to predict mortality using tree d.b.h. and scorch heights as independent variables. Fire effects are also dependent upon other factors such as season, site condition, tree age and vigor, available moisture, and occurrences of insect and disease attack [39,56]. DISCUSSION AND QUALIFICATION OF FIRE EFFECT : If fire consumes any part of tree canopy, the total leaf area is reduced, thus decreasing photosynthesis.  If burning results in damage to the bole or roots, nutrient and water transport is impaired.  Heat from fire may kill living tissue and result in a certain amount of stress [26,39,55]. Crown damage:  Crown scorch appears to be the leading factor in the majority of damage to Pacific ponderosa pine.  Estimation of percent crown volume scorch has been proven to be the best predictor of tree mortality following fire.  Crown damage is most severe in spring and early summer due to low foliar moisture content and the succulent nature of the buds and twigs [39,55].  Survival of buds is also crucial to postfire survival of Pacific ponderosa pine.  Buds can tolerate temperatures 68 degrees F (20 deg C) higher than the needles can due to their protective outer scales.  Therefore, large trees can sometimes survive a 100 percent crown scorch provided not all the buds are heat killed [26,39,44,55]. Root damage:  Following prescribed burning of old-growth Pacific ponderosa stands in Crater Lake National Park, Oregon, mortality was higher in burned areas (19.5 percent) than in unburned areas (6.6 percent).  A major factor contributing to postfire mortality was the reduction of fine roots.  Burning reduced fine-root dry weight 50 to 75 percent from 1 to 5 months after burning [64]. Bole damage:  This pine is fire tolerant because it has a fire-resistant bark containing a 1/8- to 1/4-inch (0.3-0.6 cm) thick layer at 2 inches (5 cm) diameter [77].  It also has a very moist core of high density wood that dissipates the heat energy it receives, thus protecting the bole from lethal heat levels [55].  Ryan and Frandsen [53], however, found that mature Pacific ponderosa pine trees suffered more basal injuries from smoldering fires than did immature trees because of the greater quantities of accumulated duff surrounding their boles.  Cambium damage most often occurs after the passing of high-severity fires. Young trees are most susceptible to cambium damage as a result of thinner bark and a higher occurrence of girdling [26,78].  Partially girdled trees may survive up to 25 percent basal loss if root and crown damage is minimal [71]. Season of burn:  Pacific ponderosa pine can withstand low-severity fires which generally occur during the wet months of early spring or late fall.  A dry spring fire may occur when trees are in stress during leaf and bud burst, resulting in higher mortality rates.  Trees become dormant toward fall and thus are more fire resistant.  In fall, Pacific ponderosa pine can withstand up to 50 percent crown scorch, while in spring only 30 percent [26,45]. PLANT RESPONSE TO FIRE : Pacific ponderosa pine's response to fire will vary according to fire severity, tree age, and season.  High-severity fires that occur during periods of high stress will generally result in death.  Low- to medium-severity fires will generally restrict the growth and regeneration of the tree, but recovery is usually evident the following year [39].  Immediately following fire, Pacific ponderosa pine may experience a large needle drop as a reaction to hot convectional air movement through the canopy [55].  Postfire seedling establishment:  Fire creates favorable seedbeds for seedling establishment.  The soil is often rich in available inorganic nitrogen that benefits tree growth [52].  Postfire stocking rates depend upon site characteristics, fire severity, and weather.  The potential for regeneration after fire is generally considered good [39].  On the El Dorado National Forest, California, a low-severity burn resulted in 20,000 seedlings per acre (49,400/ha) on burned sites and no seedling establishment on unburned sites [39].  In a western Montana study, Pacific ponderosa pine produced 12 percent of the total number of sound seeds found on a burned clear-cut site over a 5-year period [64].  A postfire study in the Plumas National Forest, California, found that Pacific ponderosa pine had the highest postfire percent increase of all other associated species [39].  Postfire stocking rates depend upon site characteristics, fire severity, and weather.  The potential for regeneration after fire is generally considered good [39].  In a western Montana study, Pacific ponderosa pine produced 12 percent of the total number of sound seeds found on a burned clear-cut site over a 5-year period [64].  A postfire study in the Plumas National Forest, California, found that Pacific ponderosa pine had the highest postfire percent increase of all other associated species [39]. Postfire growth and recovery:  Information concerning Pacific ponderosa pine's response after fire is variable.  This may be attributable to the beneficial effects of reduced competition and increased nutrient availability, along with the detrimental effects of damage to the crown, cambium, and roots.  Some studies found reductions in diameter and height growth [46,76], while others reported increases in postfire growth [8,46,69,73]. DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : Near the Plumas National Forest, prescribed fire in a mixed-conifer-California black oak forest with a Pacific ponderosa pine component successfully reduced fuel load. When a wildfire burned through the site previously burned under prescription, fire severity and fire suppression costs were less compared to adjacent land where fire had been excluded. For further information on this study, see the Research Paper by Moghaddas [81]. In the Blue Mountains of northeastern Oregon, thinning or burning modified stand structure and tree species composition slightly in closed-canopy Pacific ponderosa pine stands in the stem exclusion stage, while a combination of thinning and burning had greater effects. Stands were dominated by large (≥21 inches (53 cm) in diameter), 70- to 100-year-old, even-aged Pacific ponderosa pines, with smaller Rocky Mountain Douglas-firs that had regenerated after extensive partial cutting. Thinning removed 4- to 10-inch (10-25 cm) diameter ponderosa pines and Douglas-firs, while burning reduced the number of small-diameter Douglas-firs and killed Douglas-fir seedlings. Thin-and-burn treatments resulted in greatest reduction in basal area, reaching the targeted goal of 16.0 mē/ha. Thin-and-burn treatments were also most successful in reducing conifer seedling density. All treatments caused minor changes in understory vegetation. The authors suggested that repeated treatments were needed in 10 to 15 years to bring stand structure and composition more in line with historical conditions. They comment that one set of treatments is not likely to mitigate nearly 80 years of fire exclusion and fuel accumulation in low-elevation, dry forests. For further information on the effects of thinning and burning treatments on Pacific ponderosa pine and 48 other species, see the Research Project Summary of Youngblood and others' [82] study. For more information on Pacific ponderosa pine response to fire, see Fire Case Studies and these Fire Studies: FIRE MANAGEMENT CONSIDERATIONS : The last 100 years has produced unplanned, radical changes in stand structure, fuel loadings, and role of fire in Pacific ponderosa pine ecosystems [2].  Postsettlement fire suppression has resulted in dense stockings of shade-tolerant species and the increase of insects and disease.  These results have led to other concerns such as loss of timber productivity, loss of natural diversity and aesthetic values, and the increased risk of severe fire damage to homes and harvestable timber [26]. Prescribed fire:  Reduction of fuel loads beneath existing stands of Pacific ponderosa pine by the use of prescribed fire has proven useful in reducing the potential threat of wildfires, while also favoring natural regeneration of seral species through site preparation.  In western Montana, prescribed burning on an interval of 20 to 25 years is suggested to maintain seral species and open stocking.  This would also prune lower branches thus increasing timber values, while also lowering the risk of wildfire [2,22,26,39]. Nutrient depletion:  Prescribed fire often leads to the loss of volatile nutrients from the site, especially nitrogen (N).  Following a prescribed fire on a Pacific ponderosa pine site in Oregon, all periodic annual growth increments were reduced in surviving trees four growing seasons later.  Foliar N concentration was not affected by the fire; however, total foliar N content was reduced immediately after burning. Foliar N content was significantly correlated with the observed reductions in periodic annual increments [39,40].

FIRE CASE STUDIES:

SPECIES: Pinus ponderosa var. ponderosa
FIRE CASE STUDY CITATION : Habeck, R. J. 1992. Impact of prescribed burning on Pacific ponderosa pine in a sequoia-mixed conifer forest in Kings Canyon National Park, California. In: Pinus ponderosa var. ponderosa. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ []. REFERENCE : Kilgore, Bruce M. 1973. Impact of prescribed burning on a Sequoia-mixed conifer forest. In: Proceedings, Annual Tall Timbers Fire Ecology Conference; 1972 June 8-10; Lubbock, TX. No. 12. Tallahassee, FL: Tall Timbers Research Station: 345-375. [80]. SEASON/SEVERITY CLASSIFICATION :   Fall burn / Low- to Moderate-severity STUDY LOCATION :   The study site was located on the ridge of Redwood Mountain, which runs   north and south within the 3,100-acre Redwood Mountain Grove of giant   sequoia (Sequoiadendron giganteum) in Kings Canyon National Park near Three   Rivers, California. PREFIRE VEGETATIVE COMMUNITY :   Giant sequoia, white fir (Abies concolor), and sugar pine (Pinus   lambertiana) dominate the forest, with incense-cedar (Libocedrus   decurrens), Pacific ponderosa pine, and California black oak (Quercus   kelloggii) represented except in the extreme southern plots.  Shrubs and   herbs are present but rare, and grasses are almost absent.  Major shrub   species include Sierra mountain misery (Chamaebatia foliolosa) and   Sierra gooseberry (Ribes roezlii).  Graminoids include sedges (Carex   spp.).     TARGET SPECIES PHENOLOGICAL STATE :   The target phenological states were not recorded. SITE DESCRIPTION :   The elevation along the ridge ranges from 6,400 feet (1,950 m) at the   saddle to nearly 7,000 feet (2,134 m).  Hygrothermograph records show a   yearly low of 17 degrees F (-8.4 deg C) and a high of 82 degrees F (28   deg C).  Temperatures in November just before the burn ranged from 32 to   58 degrees F (0-15 deg C).  Relative humidity fluctuated between 30 and   80 percent.  Winds in and near the study plots were moderate when   present, varying from 0 to 5 mph (0.3 km/h).  Average slope was 35   percent.  Large portions of this study area are found on soils derived   from metamorphic schists.   Burn day conditions were as follows:                                               Temperature: 59 degrees F (15 deg C)                         Humidity: 20 percent                         10-hour fuel sticks: 10 grams                         Wind speed: 0 mph     FIRE DESCRIPTION :   Twelve 60- by 100-foot (18x30 m) study plots were laid out about 600   feet (183 m) east of the ridge of Redwood Mountain at an elevation of   6,300 feet (1,920 m).  Two additional plots were established just below   the saddle parking area as demonstration plots.  These were selected as   being representative of the range of vegetative and fuel conditions found   on this east-facing slope of the mountain.  Seven of the 12 plots and   one demonstration plot were burned, while the remaining plots were   retained as controls.  For each plot, the following information was   measured before and after ignition:   1. Species, diameter, height class > 6 inches d.b.h. (15 cm) or 4.5 feet      (1.4 m) tall.   2. Number of white fir and sugar pine saplings per acre in four height      classes.   3. Extent and approximate height of white fir sapling thickets.   4. Coverage and frequency values.   5. Litter and duff weights.   6. Length and diameter of down trees.   7. Chemical light meter indices for light reaching the forest floor.   8. Vegetation appearance recorded by black and white/color photographs      from 102 permanent photo points.   After all prefire measurements were made, a 2-foot (0.6 m) wide   fire-line was built along the two sides and the bottom of the proposed   5-acre (2 ha) burn area.  The burning indices for the burn day were as   follows:                          Forecast     Actual       Prescription (range)                          --------     ------       --------------------   Fine Fuel Moisture        6           5                 7-10   Spread Index              8           8                 5-12   Intensity Index          59          56                37-49   Timber Burning Index      5           5                 3-5   Ignition Index           45          55                15-49   All test plots were ignited at 0900 by drip torch along the upper   boundary of the burn area.  A strip-head fire method of ignition was   used and it burned briskly from 0900 to 1200. FIRE EFFECTS ON TARGET SPECIES :   Ninety-four percent of the 210 2- by 3-foot (0.6x0.9 m) sample plots   showed evidence of fire impact.  Eighty percent burned almost   completely, while 14 percent burned partially or lightly.  Only 6   percent of the sample plots remained unburned.  Pacific ponderosa pine   trees greater than 12 inches (0.3 m) d.b.h. showed an increase in   relative density from 7.9 percent to 8.2 percent.  This increase may be   attributable to the reduction in white fir density.  Overall, Pacific   ponderosa pine cover percent increased 0.9 percent for all size classes.   This suggests that it is relatively resistant to low- to   moderate-severity fires under these burn conditions.   Prefire measurement of litter and duff was 50 tons/acre (124 tons/ha).   Following burning, litter fuels were reduced by more than 75 percent and   duff fuels by more than 85 percent, resulting in a postfire measurement   of 7.7 tons/acre (19 tons/ha). FIRE MANAGEMENT IMPLICATIONS :   This study investigated methods by which the impacts of prescribed fire   on certain biotic and abiotic elements of the sequoia-mixed conifer   forest ecosystem could be measured.  Pacific ponderosa pine was present   as a codominant species with an estimated 3.1 trees per acre (7.6/ha).   Different fire severities were found to produced different results.  In   an earlier study, a high-severity fire created more canopy openings,   prepared better seedbeds, dispersed smoke more effectively, and consumed   surface fuels more completely than this low- to moderate-severity fire.   Options for fire management in this type of stand include a   high-severity fire followed by another moderate-severity fire 7 to 10   years later; or, alternatively implement two low-severity fires in   closer sequence in order to gradually kill young seedlings and cleanup   heavy fuels.  Both strategies would allow for more natural regeneration   of seral species, while reducing the potential threat of hazardous   wildfires.

REFERENCES

SPECIES: Pinus ponderosa var. ponderosa
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