SPECIES: Pinus ponderosa var. arizonica


INTRODUCTORY

SPECIES: Pinus ponderosa var. arizonica

 

  Arizona pine on the Coconino National Forest.
Photo by Michael G. Harrington, USFS, Fire Sciences Laboratory
AUTHORSHIP AND CITATION:
Howard, Janet L. 2003. Pinus ponderosa var. arizonica. 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/ [].

FEIS ABBREVIATION:
PINPONA
PINPON

SYNONYMS:
Pinus arizonica Engelm. [78,109]

NRCS PLANT CODE [132]:
PINAR5
PIPO

COMMON NAMES:
Arizona pine

TAXONOMY:
Pinus ponderosa var. arizonica (Engelm.) Shaw (Pinaceae) is the most widely accepted scientific name for Arizona pine [50,79,94]. It is 1 of 3 varieties of ponderosa pine (P. ponderosa Laws.): the other 2 are Pacific ponderosa pine (P. p. var. ponderosa) and interior ponderosa pine (P. p. var. scopulorum) [50,78].  The taxonomy of the ponderosa pine complex is not completely resolved. Although distinct, ponderosa pine infrataxa show differences on broad latitudinal clines. Dodge [45] described the species as "a continuation of a large group of populations from the Central American Highlands to British Columbia." There are morphological and distributional overlaps among the varieties, and disagreement among authorities regarding the geographical boundaries of ponderosa pine infrataxa including Arizona pine [37,50,85,109]. Ponderosa pine populations that extend northward into western Texas from Coahuila are classified either as P. p. var. scopulorum [50] or P. arizonica var. stormiae Mart. [76,78,109].

In this review, "ponderosa pine" refers to the species as a whole. "Southwestern ponderosa pine" refers to both Arizona pine and interior ponderosa pine of the Southwest. Pacific ponderosa pine and interior ponderosa pine are discussed in separate Fire Effects Information System reviews. Information on ponderosa pine in Texas is included in the interior ponderosa pine sreview.

Intraspecies hybridization and introgression occur between Arizona and interior ponderosa pines. Arizona and interior ponderosa pines also hybridize and introgress with Apache pine (P. engelmannii); 3-taxa hybrids (interior ponderosa Arizona Apache pine) occur occasionally [50,108].

LIFE FORM:
Tree

FEDERAL LEGAL STATUS:
No special status

OTHER STATUS:
No entry


DISTRIBUTION AND OCCURRENCE

SPECIES: Pinus ponderosa var. arizonica
GENERAL DISTRIBUTION:
Arizona pine is distributed from extreme southwestern New Mexico and southeastern Arizona south to Sonora, Chihuahua, and Durango, Mexico [50,79,94,109]. In New Mexico, it occurs in Catron, Grant, and Hidalgo counties [94]. In Arizona, it occurs in Graham, Cochise, Santa Cruz, and Pima counties [79]. The Flora of North America provides an on-line distributional map of Arizona pine in the United States.

ECOSYSTEMS [54]:
FRES20 Douglas-fir
FRES21 Ponderosa pine
FRES23 Fir-spruce
FRES35 Pinyon-juniper

STATES/PROVINCES:
AZ NM MEXICO

BLM PHYSIOGRAPHIC REGIONS [22]:
7 Lower Basin and Range

KUCHLER [84] PLANT ASSOCIATIONS:
K018 Pine-Douglas-fir forest
K019 Arizona pine forest
K021 Southwestern spruce-fir forest
K023 Juniper-pinyon woodland
K031 Oak-juniper woodlands

SAF COVER TYPES [48]:
210 Interior Douglas-fir
211 White fir
220 Rocky Mountain juniper
237 Interior ponderosa pine
239 Pinyon-juniper
240 Arizona cypress
241 Western live oak

SRM (RANGELAND) COVER TYPES [121]:
504 Juniper-pinyon pine woodland

HABITAT TYPES AND PLANT COMMUNITIES:
Arizona pine is a dominant species in ponderosa pine and pine-oak (Pinus-Quercus spp.) communities of southeastern Arizona, southwestern New Mexico, and northern Mexico. It is dominant or codominant in higher-elevation, mixed montane coniferous forests. Madrean oak woodland species are common plant associates in lower-elevation (< about 6,000 feet (1,800 m)) portions of Arizona pine forest. At higher elevations of Arizona pine forest, Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca), Rocky Mountain white fir (Abies concolor var. concolor), and Mexican white pine (P. ayachuite) are common overstory associates. Arizona pine forest ascends to interior Douglas-fir-white fir forest around 7,500 feet (2,300 m) [49,101,104], and fingers into Madrean oak and pinyon-juniper (Pinus-Juniperus spp.) woodlands and riparian communities at Arizona pine's lower elevational limits [104].

In southeastern Arizona, Arizona pine is common in and just above Madrean oak and pine-juniper woodlands. Madrean hardwood associates include Emory oak (Q. emoryi), Arizona white oak (Q. arizonica), silverleaf oak (Q. hypoleucoides), Arizona madrone (Arbutus arizonica), and Arizona sycamore (Platanus wrightii). Conifer associates include alligator juniper (Juniperus deppeana), Apache pine (Pinus engelmannii), and Chihuahua pine (P. leiophylla var. chihuahuana) [21]. Pointleaf manzanita (Arctostaphylos pungens) and longtongue muhly (Muhlenbergia longiligula) are common in the understory [26].

In the Chiricahua Mountains of southeastern Arizona, Arizona pine forest lies on elevation and moisture gradients between lower-elevation, drier Mexican pinyon (P. cembroides), Chihuahua pine, and Apache pine communities, and moister, higher-elevation southwestern white pine (P. strobiformis) communities [18]. Interior ponderosa pine sometimes codominates with Arizona pine.  Arizona pine is generally more common at lower elevations, with interior ponderosa pine occupying upper portions of ponderosa pine forest [104]. Brady and Bonham [26] found that in the Huachuca Mountains, which span the Arizona-Mexico border, Arizona pine assumed dominance at 7,498 feet (2,285 m). It codominated with silverleaf oak down to 6,989 feet (2,130 m) elevation, where silverleaf oak became dominant. Arizona pine became subdominant to Rocky Mountain Douglas-fir above 8,038 feet (2,450 m), and was not reported above 8,531 feet (2,600 m) elevation. Along with Rocky Mountain Douglas-fir, corkbark fir (Abies lasiocarpa var. arizonica) and/or Engelmann spruce (Picea engelmannii) may co-occur with Arizona pine in high elevation, mixed-conifer sites [98].

In Madrean oak woodland of northern Mexico, Arizona pine is usually subdominant to oaks. Netleaf oak (Quercus rugosa) and Chihuahuan oak (Q. chihuahuensis) are the most common community dominants; Chihuahua and Apache pines share subdominant status with Arizona pine [53]. At mid-elevations (5,440-7,250 ft (1,650-2,200 m)), Madrean oak-pine woodland ascends to higher-elevation montane forest. Handbasin (Q. pennivenia), Mexican white (Q. epileuca), silverleaf, netleaf, and/or Chihuahuan oaks join a pine-dominated, mixed formation with Arizona, Chihuahua, Apache, Durango (P. durangensis), and/or weeping (P. lumholtzii) pines. Arizona cypress (Cupressus arizonica), Arizona madrone, and Texas madrone (A. texana) are characteristic community components [27]. Pure to nearly pure stands of Arizona pine occur further south in Mexico [110].

Publications describing plant communities dominated by Arizona pine are listed below.

AZ [27,100,101,104,143]
NM [104]
Mexico [49,101,104]

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Pinus ponderosa var. arizonica
GENERAL BOTANICAL CHARACTERISTICS:
Arizona pine is a native tree. It reaches 75 to 100 feet (23-30 m) in height and 30 to 50 inches (75-130 cm) in diameter at maturity. The branches are stout, thick, and self pruning. The trunk is usually devoid of branches for half or more of its length. The crown is typically open and varies from short and conical to rounded or flat [83,89,94,109]. Bark of mature trees is about 2 inches (5 cm) thick. Needles are 4 to 9.5 inches (10-24 cm) long. The majority of needles are 4- or 5-fascicled, but some trees are 2- or 3-fascicled [45,50,94]. Average female cone length (2.5 inches (6.3 cm)) is shorter than other varieties of ponderosa pine. However, there is great between-population variation in length of Arizona pine cones [45]: they range from 1.5 to 2.4 inches (5-8 cm) long. Seeds are winged, with the seed body ranging from 3 to 4 mm in length and the wing extending to 15 mm [50,94]. Mature ponderosa pine have deep, extensive root systems [29]. Depending on the substrate, roots may penetrate to depths of 33 to 40 feet (10-12 m). Lateral root development is closely related to crown width and varies with tree density. Lateral roots may extend 100 feet (30 m) in open stands [118].

Arizona pine and interior ponderosa pine can be very similar in appearance. In a study comparing morphological traits used to distinguish Arizona and interior ponderosa pines, Dodge [45] found considerable overlap between the 2 taxa. He concluded that differences between the taxa were "minor," and that between-population morphological differences in Arizona pine were at least as pronounced as between-varietal differences in morphology. Distinguishing the 2 taxa can be further confounded by their tendency to hybridize. Arizona pine is morphologically distinguished from interior ponderosa pine by having shorter needles with a majority of 4- or 5-needled (vs. 2- or 3-needled) fascicles; smaller cones with incurved (vs. reflected) prickles; thinner bark; a rounder, more open crown; and being shorter and less broad at the base at maturity [45,50,79]. The Flora of North America provides botanical descriptions and dichotomous keys for Arizona pine and other varieties of ponderosa pine.

RAUNKIAER [112] LIFE FORM:
Phanerophyte

REGENERATION PROCESSES:
Arizona pine reproduces from seed. It is monoecious, with pollen dispersed by wind. Ponderosa pine 1st produces cones at 10 to 20 years of age [83]. Good Arizona pine seed crops are produced every 2 to 3 years [55]. High temperatures during strobili formation have been correlated with good Arizona pine cone crops [40,92]. Ponderosa pine seeds are mostly wind dispersed and do not usually carry more than 120 feet (37 m) from the parent tree [55]. Arizona pine seed (collected in Arizona and germinated in the greenhouse) showed mean viability of 75% [83]. Southwestern ponderosa pine seed germinates with the onset of mid-summer rains; germination continues until onset of fall drought. Mid-summer germinants show best survivorship, probably because they gain the most growth before onset of winter dormancy and succeeding spring drought [86].

Best Arizona pine seedling establishment occurs in early seral communities, and establishment is somewhat rare [32,114]. Several conditions are necessary for successful regeneration of southwestern ponderosa pine: 1) an adequate seed source, 2) mineral soil with lowing stocking of competing vegetation, 3) open light, 4) adequate moisture at the right time, and 5) a low rate of herbivory on seedlings. Co-occurrence of these conditions is irregular and uncommon [14,75,90,114]. A warmer than average spring results in good cone crops [29,40,92].  A disturbance such as fire is required to prepare a bare mineral seedbed and create open-light conditions [90]. Twenty-seven months after cone initiation, a wetter than average summer and fall produces good seed germination [29]. Seeds appear to require continually moist conditions for at least 7 days at temperatures above 55 degrees Fahrenheit (13 oC) [117]. Above-average precipitation the following spring promotes seedling survival [29]. A pulse of Arizona pine regeneration occurred from 1910-1930, when these conditions coincided; such a pulse has not occurred since [114]. 

SITE CHARACTERISTICS:
In the United States, Arizona pine is the least accessible of the 3 varieties of  ponderosa pine. It occupies slopes, canyons, rims, and tablelands [50]. Slopes may be steep: Arizona pine sites in the Santa Catalina Mountains of southeastern Arizona ranged from 10 to 36o. In Arizona, Arizona pine soils are mostly derived from limestone, sandstone, and quartzite overlaying schist and granite [45]. Arizona pine is most common between 7,000 and 7,500 feet (2,100-2,300 m), while interior ponderosa pine is more common above 9,000 feet (2,700 m). Elevations between 7,500 and 9,000 feet are occupied by both varieties, and by their hybrids [21,45]. Overall elevational range of Arizona pine by state is:

Arizona  6,200 to 9,840 feet (1,900-3,420 m) [12,18,50,101]
New Mexico  6,900 to 8,000 feet (2,100-2,500 m) [50]  
Sonora  7,000 to 9,000 feet (2,000-3,000 m) [45]

Climate is semi-arid to arid with bimodal rainfall. Winter rains occur from December through March and are followed by a dry season extending to June. Monsoonal rains occur from July to September, with greater than 50% of the mean annual rainfall occurring in August [17,21,26]. Total annual rainfall is highly variable, and prolonged drought is common [26].

SUCCESSIONAL STATUS:
Ponderosa pine is shade intolerant [14,75], and is often a dominant tree in southwestern sky island plant communities [98,100]. Muldavin and others [100] have identified several Arizona pine habitat types. 

Successional pathways in Arizona pine communities are poorly understood, and further research is needed in this area. Arizona pine is occasionally seral in white fir habitats [98]. Arizona pine may be a climax species on dry, mid-elevation (6,800 to 8,500 feet (2,000-2,600 m)) sites  [69,98,100,119,122]. Arizona pine types also occur on high-elevation (<9,300 feet (2,800 m)), relatively moist north- and east-facing slopes [30,100] that are maintained by frequent fire [100]. These sites may proceed to mixed-conifer forest in the absence of fire, with Arizona pine being successionally replaced by Rocky Mountain Douglas-fir and/or white fir [30,98]. At low elevations (< 6,500 feet (2,000 m)), Arizona pine understories are characterized by Arizona pine and Rocky Mountain Douglas-fir seedlings and saplings, oaks, and junipers [87]. 

SEASONAL DEVELOPMENT:
Mean date of pollen spread of Arizona pine in New Mexico was May 22 [46]. In Arizona, pollination occurred in May, 2nd-year cones ripened in September and October, and seed dispersed in October [83]. Southwestern ponderosa pine seed germinates from summer through fall. October drought initiates dormancy. Growth begins with the onset of summer rains [86].


FIRE ECOLOGY

SPECIES: Pinus ponderosa var. arizonica
FIRE ECOLOGY OR ADAPTATIONS:
Fire adaptations: Arizona pine is adapted to survive frequent low- to moderate-severity surface fires. Mature trees have thick bark, insulated buds, and a high capacity to recover from crown scorch, all of which confer resistance to surface fires [51,80,95]. Arizona pine is self pruning, which discourages torching. It has the most open crown of the 3 varieties of ponderosa pine, also reducing the likelihood of torching [145].

Ponderosa pine seedlings establish on burns from on-site seed, dropped from the crowns of surviving and fire-killed trees [123], and from off-site seed borne by wind [102].

Fire regime: The sky islands of southeastern Arizona and southwestern New Mexico have among the highest incidences of lightning-caused fires in the United States [82,116]. The lightning fire season begins in late April, peaks in June, and runs into October. Maximum lightning fire incidence is above 6,000 feet (1,800 m), directly within the Arizona pine zone [11]. The fire season occurs in late spring and early summer in southeastern Arizona and southwestern New Mexico. Increasing temperatures and sparse rainfall create extremely dry conditions in spring. By June, weak storm systems typically bring lightning but little rain [98]. Few actual lightning ignitions occur, but these typically result in large burns. July has a high incidence of lightning-ignited fires, but total area burned is less compared to June [16]. By July or August, summer rains usually render fuels too moist to burn well [16,21,98].

The historical fire regime in Arizona pine forest was primarily frequent surface fire, with occasional mixed-severity and stand-replacement fires [13,31,68,74,119,124,140]. Southwestern ponderosa pine forests have undergone a shift in physiognomy since the late 19th and early 20th centuries. Prior to that time, southwestern ponderosa pines were reported as occurring in open, parklike stands with  thick grass understories [31,77,142]. Fire return intervals for Arizona pine generally ranged from 2 to 12 years for xeric sites, and up to 15 years for mesic sites [13,31,32,34,74,77,119,142]. Dendrochronological studies in mixed Arizona-Apache-Chihuahua pine gallery forests the Chiricahua Mountains show a fire interval range of 1 to 9 years (=4.2 years) [77]. In the Arizona pine and mixed-conifer belts (7,260-8,910 ft (2,200-2,700 m)) of 1 Chiricahua watershed (Mormon Canyon), fire return intervals ranged from 1 to 17 years (=3.7 years), with a tendency for wet years to precede fire years. Lower-elevation, mostly low-severity surface fires were an important source of ignition in the mixed-confer belt, where high-severity, stand-replacement fires mixed with low- and moderate-severity surface fires [98]. These regimes were probably largely driven by lightning, but it is reported that prior to European-American settlement, Native Americans ignited fires to drive game, for warfare, and to bring rain [31,98]. Reconstructive studies show presettlement densities of ponderosa pine forest in Arizona and New Mexico ranging from 3 to 66 trees per acre (7-166/ha) [34].

Fire frequency in Rocky Mountain ponderosa pine-Arizona pine forests in southeastern Arizona was greatly reduced after Euro-American settlement in the 1870s [111,119]. The explanations for this change include livestock grazing that removed grassy fuels, fire exclusion, and climatic factors [13,31,31,34,68,74,77,111,114,119,124,140,142]. It is likely no single factor is responsible. In ponderosa pine ecosystems of northern Mexico, where fire suppression is rare, mean fire return interval is less than 5 years. On an Arizona pine site in Durango, for example, widespread fires averaging every 9 years scarred at least 25% of sampled trees [51].

Today, many acres of southwestern ponderosa pine forests are overstocked, stagnant, and accumulating large quantities of litter at the expense of the grassy understory [31,126,127]. Fire exclusion has led to the build-up of fuels and led to severe crown fires in southwestern ponderosa pine and mixed-conifer forests. These forests contain an understory of young southwestern ponderosa pine, Rocky Mountain Douglas-fir, southwestern white pine, and Gambel oak: species that are less fire-resistant and more shade-tolerant than southwestern ponderosa pines [12]. Bahre [11,12] notes that fire frequency in ponderosa pine in the Chiricahua Mountains of southeastern Arizona has decreased since European-American settlement. The fire regime has changed from frequent surface fires to large, infrequent, stand-replacing crown fires. For example, the 1994 Rattlesnake Peak Fire burned 27,000 acres (10,800 ha) in southeastern Arizona [12].

Climate and grazing: Grazing appears to reduce fire frequency in southwestern ponderosa pine forests by removing grassy understory fuels. Interactive effects of grazing and climate on fire frequency are difficult to determine. Savage and Swetnam [114] suggest that climatic factors play the larger role in determining both fire frequency and Arizona stand structure. They attribute a pulse of southwestern ponderosa pine regeneration in the early 1900's to a favorable climatic sequence, which, when coupled with the lack of fire to thin the stands, resulted in the overstocked, stagnant stands found today. In the Chuskas Mountains on the Arizona-New Mexico border, this pulse of regeneration occurred on both sites with heavy domestic sheep grazing and on sites where livestock grazing had not been practiced for decades. In the Chuskas, mean fire frequency dropped dramatically (=4.2 years before 1830; < 3 fires recorded from 1830-1950) on both heavily grazed sites and on sites that had not experienced grazing for several decades. Likewise, a strong pulse of southwestern ponderosa pine occurred on both grazed and ungrazed sites [114].

Long-term fire history studies on the northern Colorado Front Range show that interannual variability in soil moisture, rather than drought alone, is conducive to widespread fire. Fire occurrence, especially widespread fire, tends to increase 1 to 4 years after above-average moisture availability in spring-summer [136]. Similarly, fire occurrence tends to increase 2 to 3 years after above-average precipitation in winter-spring  [13,126]. Climatic variation that produces widespread, stand-replacing fire has been associated with southern oscillation events. El Nino is associated with greater soil moisture and herbaceous fuel production in spring, with fire occurrence peaking several years after El Nino events. La Nina events are associated with dry springs, with fire occurrence peaking in the same year [136]. A decline in fire frequency in interior ponderosa pine forests of the Southwest coincided with reduced El Nino-La Nina events between 1780 and 1830 [129,136]. Alternating wet and dry years resulting from El Nino-La Nina events in the mid- to late 1800s increased fire frequency [136].

Fire histories: Prior to the 1880s, surface fires burned through Arizona sky island southwestern ponderosa pine forests once or twice a decade. Fires were somewhat less frequent in higher-elevation, mixed-conifer forests [126]. In the Rincon Mountain Wilderness, fire regime in Arizona pine forest was mostly large-scale (>500 acre (200 ha)), early-season (May-July) surface fires. Mean fire return interval from 1657 to 1893 was 6.1 years, with a range of 1 to 13 years. Mean fire return interval in the mixed-conifer type from 1748 to 1996 was 9.9 years, with a range of 3 to 19 years [13].

Historical fire frequency at the ponderosa pine-oak woodland interface has been documented at 1 fire or more per decade [39,77]. In a fire history study of Madrean oak-mixed pine gallery forest in Chiricahua National Monument, Arizona, Swetnam and others [127] found an historical (1620-1890) fire regime characterized by frequent surface fires at intervals ranging from 1 to 38 years. Mean fire interval across the study site was 3.9 years; mean fire return interval for fires that scarred at least 25% of trees on the study site was 13.2 years. Species composition of the forest was southwestern ponderosa, Chihuahua, Mexican pinyon, and Apache pines, and canyon live (Quercus chrysolepis), netleaf, silverleaf, and other oaks. The authors hypothesized that the oak-pine gallery served as a conduit that allowed fire spread across elevational gradients.

Fule and Covington [52] found that in Durango, fire exclusion in Arizona pine-Durango pine-Apache pine-oak (Quercus spp.) woodland favored sprouting oaks, alders (Alnus spp.), and madrones (Arbutus spp.) over Arizona and other pines. On sites where fire exclusion was practiced, a larger proportion of pines was killed by uncontrollable wildfires due to higher fire severities compared to sites with uninterrupted fire regimes.

Fire regimes where Arizona pine is a dominant or important member of the community are summarized below.

Community or Ecosystem Dominant Species Fire Return Interval Range (years)
Engelmann spruce-subalpine fir Picea engelmannii-Abies lasiocarpa 35 to > 200 
pine-cypress forest Pinus-Cupressus spp. < 35 to 200 [9]
pinyon-juniper Pinus-Juniperus spp. < 35 [105]
Mexican pinyon Pinus cembroides 20-70 [97,127]
Colorado pinyon Pinus edulis 10-49 [105]
interior ponderosa pine* Pinus ponderosa var. scopulorum 2-10 [9]
Arizona pine Pinus ponderosa var. arizonica 2-15 [13,31,119]
Rocky Mountain Douglas-fir* Pseudotsuga menziesii var. glauca 25-100 [9]
*fire return interval varies widely; trends in variation are noted in the species summary

POSTFIRE REGENERATION STRATEGY [123]:
Tree without adventitious bud/root crown
Crown residual colonizer (on-site, initial community)
Initial off-site colonizer (off-site, initial community)
Secondary colonizer - off-site seed

FIRE EFFECTS

SPECIES: Pinus ponderosa var. arizonica
Arizona pine underburn on the Coronado National Forest. Photo by Michael G. Harrington, USFS, Fire Sciences Laboratory

IMMEDIATE FIRE EFFECT ON PLANT:
Low-severity surface fires usually kill southwestern ponderosa pine less than 3 to 5 years of age or less than 6 inches (15 cm) dbh. Mortality in the 6- to 30-inch (15-76 cm) dbh class is not unusual. Trees in dense stands and trees infected with southwestern dwarf-mistletoe are most susceptible to mortality, particularly in the smaller size classes. Pole-sized and larger trees are resistant to low-severity surface fires. Severe surface or crown fires generally kill ponderosa pine of all size classes [3,4,41,67,144,145], although some "sawtimber-sized" trees may survive severe surface fire [28].  Heavy accumulations of litter at the base of trees increase the duration and intensity of fire, making trees more susceptible to scarring. Resin deposits around an old "cat-face" may increase bark flammability and promote further injury [25].

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
Ponderosa pine can withstand extensive scorching as long as buds and twigs, which tolerate higher temperatures than needles, are not badly scorched [43,115,145]. Ponderosa pine may recover from as much as 90% scorching as long as 50% of buds and twigs survive to maintain shoot growth on defoliated branches [145]. Extensive scorching of ponderosa pine crowns may cause mortality within 3 postfire years [60,72,91]. Generally, southwestern ponderosa pine recovery is best after dormant-season scorching; trees scorched in the growing season show poorer survivorship [60,65]. After a growing-season (July) wildfire in northern Arizona, Herman [72] noted at least 65% survival for ponderosa pine greater than 8 inches (20 cm) dbh that had less than 60% crown scorch. Dieterich [43] observed 89% recovery of 6 to 14-inch (15-36 cm) dbh trees that had been up to 90% scorched by dormant-season (November) wildfire on the Coconino National Forest. Studies of postfire survivorship after scorching show mixed results, however. Davis and others [41] reported that more than 75% of ponderosa pines (5- to 11-inch (13-28 cm) dbh class) scorched more than 67% died within 2 years following a dormant-season (October) prescribed fire on the Coconino National Forest.

Dormant-season studies indicate that bud kill, which is related to fire season, is more important than foliage kill in determining chances of southwestern ponderosa pine survival after burning [60,137,138]. Wagener [138] and Harrington [65] found the minimum requirement for ponderosa pine survival was 90% or less scorch with 50% or more of buds and twigs remaining. Five years after prescribed burning on the San Juan National Forest of Colorado, Harrington [65] found significant (p=0.05) differences in mortality of  scorched interior ponderosa pine, depending upon season of burning. Mortality was lowest for fall-scorched trees (5%), and spring-scorched trees showed less mortality than summer-scorched trees (17 vs. 21%, respectively). Ninety percent of fire-damaged ponderosa pine that died had done so by postfire year 4. Most trees greater than 7.2 inches (18 cm) diameter survived fall burning even with 90% scorching. With spring and summer burning, trees less than 4 inches (10 cm) diameter died with greater than 50% scorching, while at least 90% scorching was required before trees larger than 4 inches (10 cm) in diameter were killed by spring or summer fire.

PLANT RESPONSE TO FIRE:
Fire prepares a favorable mineral seedbed for Arizona pine establishment. Germinants require mineral soil so the emerging root radicle immediately contacts soil moisture [145]. Seedling density may be great in years when favorable precipitation follows fire, resulting in "doghair" thickets if further fire does not reduce the stand [63]. Thinning by fire results in increased stem growth in remaining trees [91,99,107,134]. Removal of shrubs in southwestern ponderosa pine forests results in an increase in biomass production of overstory Arizona pines [103].

Sutherland and others [125] present a linear regression model to predict postfire radial growth of southwestern ponderosa pine after prescribed fire.

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
Watershed: Improved water availability after fire may contribute to postfire growth of Arizona pine [58]. Alain-Morales [1] studied the effects of prescribed burning on watersheds in an Arizona pine forest in northwestern Chihuahua, Mexico. Comparing fire effects under fall drought burning, 2nd-year reburning under fall drought, winter burning, and no burning treatments, he found the most significant change in water flow occurred with the fall reburn treatment. The fall reburn showed a large increase in surface water flow relative to the no burn control.

FIRE MANAGEMENT CONSIDERATIONS:
Current fire return intervals are greater than the historical range of variability for southwestern ponderosa pine forests. Magnitude of fire decline is greater at lower than higher elevations, which may aid managers in determining where management actions to reduce fuels and restore more natural fire regimes might be of highest priority [135].  The expense of excluding fire from southwestern ponderosa pine forests in an active fire year can easily exceed a billion dollars, and these costly attempts at fire suppression are not always successful. In comparison, treatments to restore southwestern ponderosa pine structure and ecological processes are modest in cost [8,120]. 

Thinning to remove small-diameter trees, accompanied by prescribed fire, has been suggested as a means of restoring structure and function to degraded southwestern ponderosa pine ecosystems [7,23,33,47,59,64,113,141]. Frequent low-severity surface fires restore ecosystem function by thinning dense stands and reducing woody debris and other organic matter on the forest floor. This can result in increased soil moisture, increased soil temperature (with accompanying rates of increased litter decomposition, soil nutrient cycling, and fine root growth), increased productivity of understory herbs and shrubs, increased basal diameter growth of overstory ponderosa pine, and favorable seedbeds [3,4,35,36]. Fire pruning of lower pine branches opens the canopy [57]. Frequent prescribed fires reduce fire hazard without damaging overstory ponderosa pine [3,4]. Biswell [23] listed several ways in which prescribed burning reduces wildfire hazard in ponderosa pine:

If several fire cycles have been missed, thinning presettlement trees and manually removing heavy fuels from the base of large trees may be necessary to in order to protect old growth from severe scorching or death [33]. Harrington [65] recommends growing-season (spring or summer) burning in southwestern ponderosa pine forests if the management objective is thinning from below, and fall prescribed burning if stand losses must be minimized. Weather parameters for prescribed burning in southwestern ponderosa pine [68], and a logistic regression model predicting probability of interior ponderosa pine mortality by tree size, scorch class, and season of injury are available [60]. 

Allen and others [5] provide ecologically based recommendations for restoring southwestern ponderosa pine. They stress that restoration programs should include natural variability in southwestern ponderosa pine stands and the reestablishment of natural processes. Managers are encouraged to fully review their recommendations. A synopsis of their principles for restoration follows [5]:

Prescriptions for mid-summer burning in Arizona pine are available in Harrington [61]. He recommends burning in summer rather than fall to achieve more complete combustion of fuels [61]. This may also reduce effects of  burning on other plants and animals, since natural fires occurred more often in June and July than in fall [21]. Prescriptions for prescribed burning in both open and closed stands of Arizona pine require measurement of litter and humus layer moisture content, relative humidity, and wind speed ranges for safe, effective burning. Recommended prescriptions for summer fires use downslope, backing fires for initial fuel reductions [61]. Beaufait [20] found that backfires in ponderosa pine needles spread more slowly and had less flame depth, longer residence time, and a higher rate of energy release than headfires.

Swetnam and Dieterich [130] recommend allowing large (> 3000 acres (1200 ha)) prescribed natural surface fires in southwestern ponderosa pine in wilderness areas such as the Gila Wilderness. Based upon their fire history research, which showed evidence of mostly extensive but also small fires, they also recommend allowing small and patchy mixed-severity fires in approved areas, subject to the limitations of wilderness boundaries, visitor safety, and management and suppression capabilities.

Models:  Fuel moisture ratings for Arizona pine stands estimated using National Fire Danger Ratings showed good correlation at the driest levels but showed differences with increasing precipitation. Empirically derived equations permit adequate estimates of actual fuel moisture for burning projects. Harrington  [62] presents a model for estimating moisture of fuels in Arizona pine.

In a comparison of fuel loads on several Arizona pine sites, Harrington [64] found large differences between the relationship of forest floor depth to fuel loading, and cautioned managers against using forest floor depth:fuel loading regression models to assess fuels without some site-specific testing. Harrington has developed a model for estimating forest floor consumption in southwestern ponderosa pine forest based upon moisture content of the H surface soil layer [66]. 

Mortality: McHugh and Kolb [96] found a model using total crown damage by fire (scorch + consumption) and bole char severity as independent variables gave the best 2-way variable model for predicting individual tree mortality for prescribed and wildfires in northern Arizona. 

Wildlife: Prescribed spring or fall burning on the Coronado National Forest of southeastern Arizona had no effect on the density of nesting pairs of 14 species of cavity-nesting birds, despite the fact that the fires destroyed more large, dead ponderosa pine snags than they created. Density of 2 species, the northern flicker and the violet-green swallow, was reduced after fires [74]. More information on this study is available in the Research Project Summary Effects of understory fire on cavity-nesting birds in Arizona pine forests.

FIRE CASE STUDY

SPECIES: Pinus ponderosa var. arizonica
FIRE CASE STUDY CITATION:
Howard, Janet L., compiler. 2001. Fuel reduction in Arizona ponderosa pine in southeastern Arizona. In: Pinus ponderosa var. arizonica. 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:
Harrington, Michael G. 1981. Preliminary burning prescriptions for ponderosa pine fuel reductions in southeastern Arizona. Res. Note RM-402. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 7 p. [61].

SEASON/SEVERITY CLASSIFICATION:
Summer/low severity

STUDY LOCATION:
The study was conducted in the Santa Catalina Mountains, 10 miles (16 km) north of Tucson, Arizona.

PREFIRE VEGETATIVE COMMUNITY:
The study stand was predominantly Arizona pine (Pinus ponderosa var. arizonica) mixed with southwestern white pine (P. strobiformis), silverleaf oak (Quercus hypoleucoides), and Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca). Forest structure was uneven-aged stands of even-aged groups. Two distinct age classes of Arizona pine occurred on the study site: open groups with large, old-growth trees, and closed groups of dense, "doghair" sapling thickets. Arizona pine comprised 65 and 87% of the trees per acre, respectively, and 91 and 79% of the basal area, respectively. Southwestern pine was subdominant in both groups and appeared to be increasing under fire exclusion. Silverleaf oaks and Douglas-firs were more common in the closed stands. Group characteristics were:

  Open groups Closed groups
Mean dbh (inches) 5.2 2.5
Density (trees/acre) 603 3,512
Basal area (ft2/acre) 206 186

TARGET SPECIES PHENOLOGICAL STATE:
Not stated. Arizona pine is in the cone development stage in late July and early August, when  burning was conducted.

SITE DESCRIPTION:
Study sites are located at 8,000 feet (2,400 m). Aspect is southwest, with 30 to 50% slopes. Mean annual precipitation is 30 inches (760 mm). Approximately 10% of the precipitation falls in spring; the other 90% is about equally distributed in summer, fall, and winter. Prefire fuel weights were:

Open groups (tons/acre) Closed groups
needles/humus 24.2 19.9
0- to 0.25-in. twigs 0.3 0.4
0.25- to 1-in. twigs 1.0 1.0
Misc. 3.2   2.1  
< 1-in. material (forest floor) 28.7 23.4
   1- to 3-in. material 0.7 0.9
> 3-in. woody material (sound) 1.0 4.0
> 3-in. wood material (rotten) 3.1   6.0  
     Total fuel loading 33.5 34.3

Fuel moisture (%) for the 3 prescribed burns follows. Data are means and 1 standard deviation. For each maturity group, means in columns followed by different letters are significantly different (p=0.05).

Maturity group Site L-layer needles F-layer needles H-layer humus
Open 1 6.4 + 1.8a 23.1 + 11.2a 88.4 + 34.1a
2 6.0 + 0.8a 6.8 + 1.6b 21.4 + 5.0b
3 4.7 + 1.3a 8.6 + 3.3b 32.4 + 10.7b
Closed 1 9.2 + 1.5a 6.4 + 16.5a 79.0 + 28.9a
2 7.6 + 1.6ab 10.7 + 0.9b 30.3 + 18.2b
3 6.0 + 1.1b 14.5 + 7.4b 53.0 + 26.0ab

FIRE DESCRIPTION:
Backfires were used on the 3 sites. The 1st site was fired on 24 July, and was subject to the most rain and least number of drying days before burning compared to the other 2 sites. A 15-day rainless period had ended 17 July, followed by rains that fell until 21 July, then 3 days of clear weather. The 2nd site was fired on 3 August, 4 days after 2 brief rains. The 3rd site was fired 22 August, 4 days after 2 weeks of rain. Except for relative humidity, burning conditions were similar among the 3 sites. Fire weather and behavior were:

 Site Temperature Relative humidity Windspeed Rate of spread Flame length Fireline intensity
  (oF) (%) (miles/h) (ft/min) (ft) (BTU/ft/sec)
1 75-78 33-41 1-4, upslope 0.51 0.3-0.6 0.3-1.8
2 71-75 45-55 1-3, upslope 0.45 0.4-0.8 0.8-3.8
3 68-74 19-28 1-4, upslope 0.54 0.5-1.0 1.2-5.7

FIRE EFFECTS ON TARGET SPECIES:
The smallest trees showed greatest mortality, increasing mean stand diameter. Greatest mortality occurred in areas that experienced greatest fuel reduction. In open groups, basal areas decreased only slightly because larger trees did not succumb to burning. Basal areas were significantly reduced in closed groups due to high mortality.  Seedling and sapling mortality, respectively, was 57% and 16% on site 1; 96& and 54 % on site 2; and 84% and 43% on site 3. Postfire changes in stand structure were as follows:

Maturity group Site Mean dbh (in.) Trees/acre Basal area (ft2/acre)
before after increase before after decrease before after decrease
Open 1 3.2 3.9 21.9 % 820 595 27.4 % 163 157 3.6 %
2 5.6 9.9 76.8 % 490 195 60.2 % 191 187 2.1 %
3 6.7 11.7 74.6 % 500 325 35.0 % 269 267 0.7 %
Closed 1 2.4 2.7 12.5 % 3,230 2,460 23.8 % 179 171 4.5 %
2 2.4 3.6 50.0 % 3,885 1,750 55.0 % 191 143 23.3 %
3 2.6 3.3 26.9 % 3,420 1,910 44.2 % 187 156 16.6 %

Crown heights of surviving Arizona pine in closed groups were raised as a result of burning, increasing the chance of surviving the next fire. In closed groups, crown height was approximately 5 feet (1.5 m) above ground before fire. After fire, crown height was raised to 8 feet (2 m) above ground on site 1, and to 14 feet (4 m) on sites 2 and 3.

Forest floor weight and depth reductions were statistically similar on sites 2 and 3, and reductions on both sites were significantly greater than reductions on site 1. Percent total forest floor fuels weights (tons/acre) and percent depth reduction of 3 forest floor layers are shown below. Data are means and 1 standard deviation. Means in columns followed by different letters are significantly different (p=0.05).

Maturity group Site Total fuels  Forest floor (< 1 in.) Needles/humus Forest floor depth
Open  1 46.2 + 16.7a 39.9 + 12.9a 35.8 + 13.6a 52.8 + 6.5a
2 74.8 + 6.5b 78.7 + 5.2b 77.0 + 8.8b 80.5 + 5.7b
3 60.3 + 9.9ab 62.3 + 11.2b 62.1 + 12.2b 64.5 + 6.8a
Closed 1 34.1 + 10.5a 36.0 + 9.0a 33.3 + 12.8a 43.1 + 6.0a
2 53.9 + 9.8b 67.4 + 4.5b 67.4 + 3.6b 74.6 + 9.4b
3 54.2 + 8.4b 58.7 + 5.9b 55.6 + 9.8b 62.1 + 9.1b

In the 3-inch size class, more fuels were consumed on open sites than on closed sites. Consumption was highly variable for these larger fuels, and statistical comparisons were not made for larger fuels. Percent weight reduction of 3-inch woody fuels was:

Maturity group Site Sound Rotten Total
Open 1 64.8 74.7 73.6
2 20.9 56.5 40.1
3 67.2 54.5 57.6
Closed 1 38.5 23.8 31.1
2 6.5 47.7 29.2
3 39.9 43.2 42.6

FIRE MANAGEMENT IMPLICATIONS:
Summer prescribed burning effectively reduced fuels, and the fires were completely controllable. Individual or group crowning occurred mostly in Arizona pine thickets, where thinning may be beneficial. Harrington [61] provides the following preliminary burning prescription for fuel reduction in Arizona pine stands in the Santa Catalina Mountains:

Maturity group L-layer moisture H-layer moisture Forest floor reduction
Open 5-7 15-25 75-85
5-7 30-40 55-65
5-7 75-90 30-40
Closed 6-9 25-35 65-75
6-9 50-80 50-60
6-9 70-85 30-40

MANAGEMENT CONSIDERATIONS

SPECIES: Pinus ponderosa var. arizonica
WOOD PRODUCTS VALUE:
Ponderosa pine is the most commercially valuable and productive timber tree in the Southwest [24,56]; however, as of this writing (2002), logging of Arizona pine is limited to hazard tree removal and understory thinning [71].

IMPORTANCE TO LIVESTOCK AND WILDLIFE:
Ponderosa pine seeds are valuable food for a variety of birds, rodents, and lagomorphs [93,131].  Abert's squirrel, which have been introduced into Arizona pine's range, are ecologically dependent upon ponderosa pine [81]. Porcupines and smaller rodents eat ponderosa pine bark and wood [93]. Deer eat ponderosa pine buds early in spring when elongation begins, and occasionally eat woody shoots [106].

Arizona pine forests are critical habitat for many bird species, supporting, for example, breeding populations of Mexican junco and Mexican chickadee. Sky island populations of Arizona pine play important biogeographic roles in the distribution and survival of neotropical birds [42]. Cavity-nesting birds use southwestern ponderosa pine snags for foraging and roosting as well as nesting [15,35]. Reintroduced and rare in southeastern Arizona, thick-billed parrots are ecologically dependent on Chihuahua and southwestern ponderosa pines for food and shelter. Pine seeds are their primary diet item, and the parrots nest in pine snag cavities [73]. Many bird species use southwestern ponderosa pine needles for nesting material [93].

PALATABILITY:
Mature Arizona pine browse is unpalatable to livestock, although cattle may browse young trees [133,139]. Deer prefer southwestern ponderosa pine browse, typically selecting it above all other tree forage except quaking aspen (Populus tremuloides). Southwestern ponderosa pine germinants are browsed by a variety of bird species [75].

NUTRITIONAL VALUE:
No entry

COVER VALUE:
Southwestern ponderosa pine provides good year-round cover for songbirds, upland gamebirds, small mammals, carnivores, and ungulates. Many species of birds, including cavity nesters, use large trees for roosting and nesting cover [42,44,93].

VALUE FOR REHABILITATION OF DISTURBED SITES:
No entry

OTHER USES:
Arizona pine provides watershed protection [83].

OTHER MANAGEMENT CONSIDERATIONS:
Disease agents: Arizona pine is susceptible to several important pathogens, and to insect infestations. Southwestern pine dwarf-mistletoe (Arceuthobium vaginatum ssp. cryptopodum) is a serious disease agent of southwestern ponderosa pine. It has infected as much as 33% of ponderosa pine stands in Arizona and New Mexico [88].  Bark beetles are also serious pests. In the Southwest, pine engraver beetles (Ips spp.) often kill more ponderosa pine than do pine beetles (Dendroctonus adjunctus) [4,102]. 

Bark beetle (Ips spp. and D. adjunctus) kill has escalated greatly in the Southwest. Prolonged drought and high tree density have probably increased the susceptibility of southwestern ponderosa pine to attacks. A 2002 survey of National Forests in Arizona and New Mexico showed a 4-fold increase in ponderosa pine mortality in 2002, with over 2 million pines killed on approximately a half-million acres. The extent of defoliation of southwestern ponderosa pine on the Coronado National Forest as of 2002 was estimated at 7,451 acres (2,980 ha) from pine engraver beetles and 6,542 acres (2,617 ha) from drought. A combination of actions including removing infested trees, application of insecticide, and thinning is recommended for control. Because the beetle outbreak is so large, control efforts are best targeted to accessible, high-value areas [6].

The most serious wood-decaying fungi are red rot and western gall rust. Shoestring root rot occasionally infects pole-sized and younger trees [4]. Armillaria (Armillaria spp.) is another common fungal pathogen [70]. Management and harvesting guidelines to minimize armillaria infection are available [3,4,70].

Grazing: Southwestern ponderosa pine is resistant to moderate-intensity and lighter browsing [38]. Thirteen years after exclosures were built, ponderosa pine in southeastern Arizona had increased slightly on both ungrazed and grazed plots, at 6% frequency and 5% frequency, respectively. Initial frequency was 2% on both plots [2].

Summaries on the silviculture of southwestern ponderosa pine are available [,69,75,102].


Pinus ponderosa var. arizonica: References


1. Alanis-Morales, Hector E. 1996. Prescribed fire in the pine forests of northwestern Chihuahua. In: Ffolliott, Peter F.; DeBano, Leonard F.; Baker, Malchus, B., Jr.; [and others], tech. coords. Effects of fire on Madrean Province ecosystems: a symposium proceedings; 1996 March 11-15; Tucson, AZ. Gen. Tech. Rep. RM-GTR-289. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 193-194. [28077]

2. Alexander, Billy G., Jr.; Ronco, Frank, Jr.; Fitzhugh, E. Lee; Ludwig, John A. 1984. A classification of forest habitat types of the Lincoln National Forest, New Mexico. Gen. Tech. Rep. RM-104. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 29 p. [300]

3. Alexander, Robert R. 1986. Silvicultural systems and cutting methods for ponderosa pine forests in the Front Range of the central Rocky Mountains. Gen. Tech. Rep. RM-128. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 22 p. [13072]

4. Alexander, Robert R. 1987. Silvicultural systems, cutting methods, and cultural practices for Black Hills ponderosa pine. Gen. Tech. Rep. RM-139. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 32 p. [305]

5. Allen, Craig D.; Savage, Melissa; Falk, Donald A.; Suckling, Kieran F.; Swetnam, Thomas W.; Schulke, Todd; Stacey, Peter B.; Morgan, Penelope; Hoffman, Martos; Klingel, Jon T. 2002. Ecological restoration of southwestern ponderosa pine ecosystems: a broad perspective. Ecological Applications. 12(5): 1418-1433. [43210]

6. Anhold, John. 2002. [Forest Service memo to Arizona Forest Supervisors]. October 29. 4 leaves. 2002 forest insect and disease aerial detection survey results. On file at: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT; RWU 4403 files. [44430]

7. Arno, Stephen F. 1988. Fire ecology and its management implications in ponderosa pine forests. In: Baumgartner, David M.; Lotan, James E., compilers. Ponderosa pine: The species and its management: Symposium proceedings; 1987 September 29 - October 1; Spokane, WA. Pullman, WA: Washington State University, Cooperative Extension: 133-139. [9410]

8. Arno, Stephen F. 1996. The concept: restoring ecological structure and process in ponderosa pine forests. In: Hardy, Colin C.; Arno, Stephen F., eds. The use of fire in forest restoration: A general session at the annual meeting of the Society for Ecological Restoration; 1995 September 4-16; Seattle, WA. Gen. Tech. Rep. INT-GTR-341. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 37-38. [28669]

9. Arno, Stephen F. 2000. Fire in western forest ecosystems. In: Brown, James K.; Smith, Jane Kapler, eds. Wildland fire in ecosystems: Effects of fire on flora. Gen. Tech. Rep. RMRS-GTR-42-vol. 2. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 97-120. [36984]

10. Arnold, Joseph F.; Jameson, Donald A.; Reid, Elbert H. 1964. The pinyon-juniper type of Arizona: effects of grazing, fire and tree control. Production Research Report No. 84. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 28 p. [353]

11. Bahre, Conrad J. 1995. Human disturbance and vegetation in Arizona's Chiricahua Mountains in 1902. Desert Plants. [Volume unknown]: 41-45. [26028]

12. Bahre, Conrad J. 1998. Late 19th century human impacts on the woodlands and forests of southeastern Arizona's sky islands. Desert Plants. 14(1): 8-21. [28878]

13. Baisan, Christopher H.; Swetnam, Thomas W. 1990. Fire history on a desert mountain range: Rincon Mountain Wilderness, Arizona, U.S.A. Canadian Journal of Forest Research. 20: 1559-1569. [14986]

14. Baker, Frederick S. 1949. A revised tolerance table. Journal of Forestry. 47: 179-181. [20404]

15. Balda, Russell P. 1975. Vegetation structure and breeding bird diversity. In: Smith, Dixie R., technical coordinator. Proceedings of the symposium on management of forest and range habitats for nongame birds; 1975 May 6-9; Tucson, AZ. Gen. Tech. Rep. WO-1. Washington, DC: U.S. Department of Agriculture, Forest Service: 59-80. [17768]

16. Barrows, Jack S. 1978. Lightning fires in southwestern forests. Final report: Cooperative Agreement 16-156 CA. Unpublished report on file with: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT. 154 p. [40057]

17. Barton, Andrew M. 1993. Factors controlling plant distributions: drought, competition, and fire in montane pines in Arizona. Ecological Monographs. 63(4): 367-397. [22894]

18. Barton, Andrew M.; Teeri, James A. 1993. The ecology of elevational positions in plants: drought resistance in five montane pine species in southwestern Arizona. American Journal of Botany. 80(1): 15-25. [20527]

19. Baumgartner, David M.; Lotan, James E., compilers. 1988. Ponderosa pine: The species and its management: Symposium proceedings; 1987 September 29-October 1; Spokane, WA. Pullman, WA: Washington State University, Cooperative Extension. 281 p. [9394]

20. Beaufait, William R. 1965. Characteristics of backfires and headfires in a pine needle fuel bed. Res. Note INT-39. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 7 p. [8099]

21. Bennett, Peter S.; Kunzmann, Michael R. 1992. The applicability of generalized fire prescriptions to burning of Madrean evergreen forest and woodland. Journal of the Arizona-Nevada Academy of Science. 24-25: 79-84. [18324]

22. Bernard, Stephen R.; Brown, Kenneth F. 1977. Distribution of mammals, reptiles, and amphibians by BLM physiographic regions and A.W. Kuchler's associations for the eleven western states. Tech. Note 301. Denver, CO: U.S. Department of the Interior, Bureau of Land Management. 169 p. [434]

23. Biswell, Harold H.; Kallander, Harry R.; Komarek, Roy; [and others]. 1973. Ponderosa fire management. Misc. Publ. No. 2. Tallahassee, FL: Tall Timbers Research Station. 49 p. [4691]

24. Blatner, Keith A.; Govett, Robert L. 1988. Ponderosa pine lumber market. In: Baumgartner, David M.; Lotan, James E., compilers. Ponderosa pine: The species and its management: Symposium proceedings; 1987 September 29 - October 1; Spokane, WA. Pullman, WA: Washington State University, Cooperative Extension: 7-9. [9396]

25. Bradley, Anne F.; Noste, Nonan V.; Fischer, William C. 1992. Fire ecology of forests and woodlands in Utah. Gen. Tech. Rep. INT-287. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 128 p. [18700]

26. Brady, Ward; Bonham, Charles D. 1976. Vegetation patterns on an altitudinal gradient, Huachuca Mountains, Arizona. The Southwestern Naturalist. 21(1): 55-66. [21659]

27. Brown, David E. 1982. Madrean evergreen woodland. In: Brown, David E., ed. Biotic communities of the American Southwest--United States and Mexico. Desert Plants. 4(1-4): 59-65. [8886]

28. Campbell, R. E.; Baker, M. B., Jr.; Ffolliott, P. F.; [and others]. 1977. Wildfire effects on a ponderosa pine ecosystem: an Arizona case study. Res. Pap. RM-191. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 12 p. [4715]

29. Conkle, M. Thompson; Critchfield, William B. 1988. Genetic variation and hybridization of ponderosa pine. In: Baumgartner, David M.; Lotan, James E., compilers. Ponderosa pine: The species and its management: Symposium proceedings; 1987 September 29 - October 1; Spokane, WA. Pullman, WA: Washington State University, Cooperative Extension: 27-43. [9399]

30. Conner, Jerry. 2002. [E-mail to Robert Lefevre]. January 3. On file at: U.S. Department of Agriculture, Forest Service, Fires Sciences Laboratory, Missoula, MT; RWU 4403 files. [40252]

31. Cooper, Charles F. 1960. Changes in vegetation, structure, and growth of southwestern pine forests since white settlement. Ecological Monographs. 30(2): 129-164. [3927]

32. Cooper, Charles F. 1961. Pattern in ponderosa pine forests. Ecology. 42(3): 493-499. [5780]

33. Covington, W. W.; Moore, M. M. 1992. Postsettlement changes in natural fire regimes: implications for restoration of old-growth ponderosa pine forests. In: Kaufmann, Merrill R.; Moir, W. H.; Bassett, Richard L., technical coordinators. Old-growth forests in the Southwest and Rocky Mountain regions: Proceedings of a workshop; 1992 March 9-13; Portal, AZ. Gen. Tech. Rep. RM-213. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 81-99. [19045]

34. Covington, W. W.; Moore, M. M. 1994. Postsettlement changes in natural fire regimes and forest structure: ecological restoration of old-growth ponderosa pine forests. Journal of Sustainable Forestry. 2(1/2): 153-181. [30532]

35. Covington, W. Wallace; Fule, Peter Z.; Moore, Margaret M.; [and others]. 1997. Restoring ecosystem health in ponderosa pine forests of the Southwest. Journal of Forestry. 95(4): 23-29. [27618]

36. Covington, W. Wallace; Sackett, Stephen S. 1984. The effect of a prescribed burn in Southwestern ponderosa pine on organic matter and nutrients in woody debris and forest floor. Forest Science. 30(1): 183-192. [7624]

37. Cronquist, Arthur; Holmgren, Arthur H.; Holmgren, Noel H.; Reveal, James L. 1972. Intermountain flora: Vascular plants of the Intermountain West, U.S.A. Vol. 1. New York: Hafner Publishing Company, Inc. 270 p. [717]

38. Currie, Pat O. 1975. Grazing management of ponderosa pine-bunchgrass ranges of the central Rocky Mountains. Res. Pap. RM-159. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 24 p. [12600]

39. Danzer, Shelley R.; Baisan, Chris H.; Swetnam, Thomas W. 1996. The influence of fire and land-use history on stand dynamics in the Huachuca Mountains of southeastern Arizona. In: Ffolliott, Peter F.; DeBano, Leonard F.; Baker, Malchus, B., Jr.; [and others], tech. coords. Effects of fire on Madrean Province ecosystems: a symposium proceedings; 1996 March 11-15; Tucson, AZ. Gen. Tech. Rep. RM-GTR-289. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 265-270. [28111]

40. Daubenmire, R. 1960. A seven-year study of cone production as related to xylem layers and temperature in Pinus ponderosa. The American Midland Naturalist. 64(1): 187-193. [37425]

41. Davis, James R.; Ffolliott, Peter F.; Clary, Warren P. 1968. A fire prescription for consuming ponderosa pine duff. Res. Note RM-115. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 4 p. [11988]

42. Diem, Kenneth L.; Zeveloff, Samuel I. 1980. Ponderosa pine bird communities. In: DeGraaf, Richard M., technical coordinator. Management of western forests and grasslands for nongame birds: Workshop proceedings; 1980 February 11-14; Salt Lake City, UT. Gen. Tech. Rep. INT-86. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station: 170-197. [17905]

43. Dieterich, John H. 1979. Recovery potential of fire-damaged Southwestern ponderosa pine. Res. Note RM-379. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 8 p. [4698]

44. Dittberner, Phillip L.; Olson, Michael R. 1983. The plant information network (PIN) data base: Colorado, Montana, North Dakota, Utah, and Wyoming. FWS/OBS-83/86. Washington, DC: U.S. Department of the Interior, Fish and Wildlife Service. 786 p. [806]

45. Dodge, Richard Archie. 1963. Investigations into the ecological relationships of ponderosa pine in southwest Arizona. Tucson, AZ: University of Arizona. 118 p. Dissertation. [20315]

46. Duffield, J. W. 1953. Pine pollen collection dates--annual and geographic variation. For. Res. Notes No. 85. Berkeley, CA: U.S. Department of Agriculture, Forest Service, California Forest and Range Experiment Station. 9 p. [17970]

47. Edminster, Carleton B.; Olsen, William K. 1996. Thinning as a tool in restoring and maintaining diverse structure in stands of Southwestern ponderosa pine. In: Covington, Wallace; Wagner, Pamela K., technical coordinators. Conference on adaptive ecosystem restoration and management: restoration of Cordilleran conifer landscapes of North America: Proceedings; 1996 June 6-8; Flagstaff, AZ. Gen. Tech. Rep. RM-GTR-278. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 62-68. [26925]

48. Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Washington, DC: Society of American Foresters. 148 p. [905]

49. Felger, Richard S.; Johnson, Matthew B. 1995. Trees of the northern Sierra Madre Occidental and sky islands of southwestern North America. In: DeBano, Leonard F.; Ffolliott, Peter F.; Ortega-Rubio, Alfredo; [and others], technical coordinators. Biodiversity and management of the Madrean Archipelago: the sky islands of southwestern United States and northwestern Mexico: Proceedings; 1994 September 19-23; Tucson, AZ. Gen. Tech. Rep. RM-GTR-264. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 71-83. [26233]

50. Flora of North America Association. 2000. Flora of North America north of Mexico. Volume 2: Pteridophytes and gymnosperms, [Online]. Available: http://hua.huh.harvard.edu/FNA/ [2002, March 27]. [36990]

51. Fule, Peter Z.; Covington, W. Wallace. 1997. Fire regimes and forest structure in the Sierra Madre Occidental, Durango, Mexico. Acta Botanica Mexicana. 41: 43-79. [29647]

52. Fule, Peter Z.; Covington, W. Wallace. 1998. Spatial patterns of Mexican pine-oak forests under different recent fire regimes. Plant Ecology. 134(2): 197-209. [28600]

53. Gallina, Sonia; Ffolliott, Peter F. 1983. Overstory-understory relationships: oak-pine forests of Sierra Madre Occidental, Mexico. In: Bartlett, E. T.; Betters, David R., eds. Overstory-understory relationships in western forests. Western Regional Res. Publ. No. 1. Fort Collins, CO: Colorado State University Experiment Station: 19-20. [3312]

54. Garrison, George A.; Bjugstad, Ardell J.; Duncan, Don A.; Lewis, Mont E.; Smith, Dixie R. 1977. Vegetation and environmental features of forest and range ecosystems. Agric. Handb. 475. Washington, DC: U.S. Department of Agriculture, Forest Service. 68 p. [998]

55. Gartner, F. Robert; Thompson, Wesley W. 1973. Fire in the Black Hills forest-grass ecotone. In: Proceedings, annual Tall Timbers fire ecology conference; 1972 June 8-9; Lubbock, TX. No. 12. Tallahassee, FL: Tall Timbers Research Station: 37-68. [1002]

56. Gottfried, Gerald J. 1978. Five-year growth and development in a virgin Arizona mixed conifer stand. Res. Pap. RM-203. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 22 p. [15661]

57. Grier, Bob. 1981. Burning with a purpose. Nebraskaland. 59(3): 38-42. [15545]

58. Haase, Sally M. 1986. Effect of prescribed burning on soil moisture and germination of southwestern ponderosa pine seed on basaltic soils. Res. Note RM-462. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 6 p. [4741]

59. Hardy, Colin C.; Arno, Stephen F., eds. 1996. The use of fire in forest restoration: A general session at the annual meeting of the Society for Ecological Restoration; 1995 September 14-16; Seattle, WA. Gen. Tech. Rep. INT-GTR-341. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 86 p. [26833]

60. Harrington, M. G. 1993. Predicting Pinus ponderosa mortality from dormant season and growing season injury. International Journal of Wildland Fire. 3(2): 65-72. [21360]

61. Harrington, Michael G. 1981. Preliminary burning prescriptions for ponderosa pine fuel reductions in southeastern Arizona. Res. Note RM-402. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 7 p. [20326]

62. Harrington, Michael G. 1982. Estimating ponderosa pine fuel moisture using national fire-danger rating moisture values. Res. Pap. RM-233. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 7 p. [4695]

63. Harrington, Michael G. 1982. Stand, fuel, and potential fire behavior characteristics in an irregular southeastern Arizona ponderosa pine stand. Res. Note RM-418. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 6 p. [4703]

64. Harrington, Michael G. 1986. Comparison of forest floor depth to loading relationships from several Arizona ponderosa pine stands. Res. Note RM-463. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 5 p. [20327]

65. Harrington, Michael G. 1987. Ponderosa pine mortality from spring, summer, and fall crown scorching. Western Journal of Applied Forestry. 2: 14-16. [4978]

66. Harrington, Michael G. 1987. Predicting reduction of natural fuels by prescribed burning under ponderosa pine in southeastern Arizona. Res. Note RM-472. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 4 p. [4725]

67. Harrington, Michael G.; Hawksworth, Frank G. 1990. Interactions of fire and dwarf mistletoe on mortality of southwestern ponderosa pine. In: Krammes, J. S., technical coordinator. Effects of fire management of southwestern natural resources: Proceedings of the symposium; 1988 November 15-17; Tucson, AZ. Gen. Tech. Rep. RM-191. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 234-240. [11296]

68. Harrington, Michael G.; Sackett, Stephen S. 1992. Past and present fire influences on Southwestern ponderosa pine old growth. In: Kaufmann, Merrill R.; Moir, W. H.; Bassett, Richard L., technical coordinators. Old-growth forests in the Southwest and Rocky Mountain regions: Proceedings of a symposium; 1992 March 9-13; Portal, AZ. Gen. Tech. Rep. RM-213. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 44-50. [21977]

69. Harrington, Michael. 2001. [E-mail to Janet Howard]. September 24. Missoula, MT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. On file at: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT; RWU 4403 files. [40253]

70. Hawksworth, Frank G.; Shaw, Charles G., III. 1988. Damage and control of major diseases of ponderosa pine. In: Baumgartner, David M.; Lotan, James E., compilers. Ponderosa pine: The species and its management: Symposium proceedings; 1987 September 29 - October 1; Spokane, WA. Pullman, WA: Washington State University, Cooperative Extension: 99-108. [9405]

71. Hensel, Steve. 2002. [E-mail to Robert Lefevre]. January 3. Tucson, AZ: U.S. Department of Agriculture, Forest Service, Coronado National Forest, Santa Catalina Ranger District. On file at: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT; RWU 4403 files. [40250]

72. Herman, F. R. 1950. Survival of fire-damaged ponderosa pine. Research Note No. 119. Tucson, AZ: U.S. Department of Agriculture, Forest Service, Southwestern Forest and Range Experiment Station. 3 p. [4705]

73. Hoffman, George R.; Alexander, Robert R. 1987. Forest vegetation of the Black Hills National Forest of South Dakota and Wyoming: a habitat type classification. Res. Pap. RM-276. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 48 p. [1181]

74. Horton, Scott P.; Mannan, R. William. 1988. Effects of prescribed fire on snags and cavity-nesting birds in southeastern Arizona pine forests. Wildlife Society Bulletin. 16: 37-44. [5549]

75. Jones, John R. 1974. Silviculture of southwestern mixed conifers and aspen: The status of our knowledge. Res. Pap. RM-122. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 44 p. [16081]

76. Jones, Stanley D.; Wipff, Joseph K.; Montgomery, Paul M. 1997. Vascular plants of Texas. Austin, TX: University of Texas Press. 404 p. [28762]

77. Kaib, Mark; Baisan, Christopher H.; Grissino-Mayer, Henri D.; Swetnam, Thomas W. 1996. Fire history in the gallery pine-oak forests and adjacent grasslands of the Chiricahua Mountains of Arizona. In: Ffolliott, Peter F.; DeBano, Leonard F.; Baker, Malchus, B., Jr.; [and others], tech. coords. Effects of fire on Madrean Province ecosystems: a symposium proceedings; 1996 March 11-15; Tucson, AZ. Gen. Tech. Rep. RM-GTR-289. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 253-264. [28109]

78. Kartesz, John T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. Volume I--checklist. 2nd ed. Portland, OR: Timber Press. 622 p. [23877]

79. Kearney, Thomas H.; Peebles, Robert H.; Howell, John Thomas; McClintock, Elizabeth. 1960. Arizona flora. 2d ed. Berkeley, CA: University of California Press. 1085 p. [6563]

80. Keeley, Jon E.; Zedler, Paul H. 1998. Evolution of life histories in Pinus. In: Richardson, David M., ed. Ecology and biogeography of Pinus. Cambridge, United Kingdom: The Press Syndicate of the University of Cambridge: 219-250. [37705]

81. Keith, James O. 1965. The Abert squirrel and its dependence on ponderosa pine. Ecology. 46: 150-163. [1320]

82. Komarek, E. V., Sr. 1968. The nature of lightning fires. In: Proceedings, California Tall Timbers fire ecology conference; 1967 November 9-10; Hoberg, CA. No. 7. Tallahassee, FL: Tall Timbers Research Station: 5-41. [18442]

83. Krugman, Stanley L.; Jenkinson, James L. 1974. Pinus L. pine. In: Schopmeyer, C. S., tech. cood. Seeds of woody plants in the United States. Agric. Handb. 450. Washington, D.C.: U.S. Department of Agriculture, Forest Service: 598-638. [37725]

84. Kuchler, A. W. 1964. United States [Potential natural vegetation of the conterminous United States]. Special Publication No. 36. New York: American Geographical Society. 1:3,168,000; colored. [3455]

85. Lackschewitz, Klaus. 1991. Vascular plants of west-central Montana--identification guidebook. Gen. Tech. Rep. INT-227. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 648 p. [13798]

86. Larson, M. M. 1961. Seed size, germination dates, and survival relationships of ponderosa pine in the Southwest. Research Note No. 66. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 4 p. [5044]

87. Lefevre, Robert. 2002. [E-mail to Janet Howard]. January 15. Tucson, AZ: U.S. Department of Agriculture, Forest Service, Coronado National Forest. On file at: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fires Sciences Laboratory, Missoula, MT; RWU 4403 files. [40251]

88. Lightle, Paul C.; Weiss, Melvyn J. 1974. Dwarf mistletoe of ponderosa pine in the Southwest. Forest Pest Leaflet 19. Washington, D.C.: U.S. Department of Agriculture, Forest Service. 8 p. [1454]

89. Little, Elbert L., Jr. 1950. Southwestern trees: A guide to the native species of New Mexico and Arizona. Agric. Handb. 9. Washington, DC: U.S. Department of Agriculture, Forest Service. 109 p. [20317]

90. Lowdermilk, W. C. 1930. Influence of forest litter on run-off, percolation, and erosion. Journal of Forestry. 28: 474-491. [5908]

91. Lynch, Donald W. 1959. Effects of a wildfire on mortality and growth of young ponderosa pine trees. Res. Note No. 66. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 8 p. [4748]

92. Maguire, William P. 1956. Are ponderosa pine cone crops predictable? Journal of Forestry. 54: 778-779. [37483]

93. Martin, Alexander C.; Zim, Herbert S.; Nelson, Arnold L. 1951. American wildlife and plants. New York: McGraw-Hill Book Company, Inc. 500 p. [4021]

94. Martin, William C.; Hutchins, Charles R. 1981. A flora of New Mexico. Volume 2. Germany: J. Cramer. 2589 p. [37175]

95. McCune, Bruce. 1988. Ecological diversity in North American pines. American Journal of Botany. 75(3): 353-368. [5651]

96. McHugh, Charles W.; Kolb, Thomas E. 2003. Ponderosa pine mortality following fire in northern Arizona. International Journal of Wildland Fire. 12: 1-16. [43550]

97. Moir, William H. 1982. A fire history of the High Chisos, Big Bend National Park, Texas. The Southwestern Naturalist. 27(1): 87-98. [5916]

98. Morino, Kiyomi A.; Baisan, Christopher H.; Swetnam, Thomas W. 2000. Historical fire regimes in the Chiricahua Mountains, Arizona: an examination of fire along an elevation gradient and in mixed-conifer forest. Final report. USFS Cooperative Agreement #28-C4-858: Sub-project IV/Amendment 6. On file with: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Lab, Missoula, MT. 82 p. [40058]

99. Morris, William G.; Mowat, Edwin L. 1958. Some effects of thinning a ponderosa pine thicket with a prescribed fire. Journal of Forestry. 56: 203-209. [8109]

100. Muldavin, Esteban H.; De Velice, Robert L.; Ronco, Frank, Jr. 1996. A classification of forest habitat types: Southern Arizona and portions of the Colorado Plateau. RM-GTR-287. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 130. [27968]

101. Muldavin, Esteban H.; DeVelice, Robert L. 1987. A forest habitat type classification of southern Arizona and its relationship to forests of the Sierra Madre Occidental of Mexico. In: Aldon, Earl F.; Gonzales Vicente, Carlos E.; Moir, William H., technical coordinators. Strategies for classification and management of native vegetation for food production in arid zones: Proceedings; 1987 October 12-16; Tucson, AZ. Gen, Tech. Rep. RM-150. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 24-31. [2728]

102. Oliver, William W.; Ryker, Russell A. 1990. Pinus ponderosa Dougl. ex Laws. ponderosa pine. In: Burns, Russell M.; Honkala, Barbara H., technical coordinators. Silvics of North America. Volume 1. Conifers. Agric. Handb. 654. Washington, DC: U.S. Department of Agriculture, Forest Service: 413-424. [13399]

103. Oren, R.; Waring, R. H.; Stafford, S. G.; Barrett, J. W. 1987. Twenty-four years of ponderosa pine growth in relation to canopy leaf area and understory competition. Forest Science. 33(2): 538-547. [20318]

104. Pase, Charles P.; Brown, David E. 1982. Rocky Mountain (Petran) and Madrean montane conifer forests. In: Brown, David E., ed. Biotic communities of the American Southwest--United States and Mexico. Desert Plants. 4(1-4): 43-48. [8885]

105. Paysen, Timothy E.; Ansley, R. James; Brown, James K.; [and others]. 2000. Fire in western shrubland, woodland, and grassland ecosystems. In: Brown, James K.; Smith, Jane Kapler, eds. Wildland fire in ecosystems: Effects of fire on flora. Gen. Tech. Rep. RMRS-GTR-42-volume 2. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 121-159. [36978]

106. Pearson, G. A. 1950. Management of ponderosa pine in the Southwest. Agriculture Monograph No. 6. Washington, DC: U.S. Department of Agriculture, Forest Service. 218 p. [6565]

107. Pearson, H. A.; Davis, J. R.; Schubert, G. H. 1972. Effects of wildfire on timber and forage production in Arizona. Journal of Range Management. 25: 250-253. [5664]

108. Peloquin, R. L. 1984. The identification of three-species hybrids in the ponderosa pine complex. The Southwestern Naturalist. 29(1): 115-122. [20320]

109. Perry, Jesse P., Jr. 1991. The pines of Mexico and Central America. Portland, OR: Timber Press. 231 p. [20328]

110. Perry, Jesse P., Jr.; Graham, Alan; Richardson, David M. 1998. The history of pines in Mexico and Central America. In: Richardson, David M., ed. Ecology and biogeography of Pinus. Cambridge, UK: The Press Syndicate of the University of Cambridge: 137-149. [37700]

111. Pyne, Stephen J.; Andrews, Patricia L.; Laven, Richard D. 1984. Introduction to wildland fire. 2nd ed. New York: Wiley & Sons, Inc. 769 p. [37243]

112. Raunkiaer, C. 1934. The life forms of plants and statistical plant geography. Oxford: Clarendon Press. 632 p. [2843]

113. Sackett, Stephen; Haase, Sally; Harrington, M. G. 1993. Restoration of southwestern ponderosa pine ecosystems with fire. In: Covington, M. Wallace; Debano, Leonard F.; Covington, W. W., tech. coords. Sustainable ecological systems: implementing an ecological approach to land management: Proceedings; 1993 July 12-15; Flagstaff, AZ. Gen. Tech. Rep. RM-247. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 115-121. [37424]

114. Savage, Melissa; Swetnam, Thomas W. 1990. Early 19th-century fire decline following sheep pasturing in a Navajo ponderosa pine forest. Ecology. 71(6): 2374-2378. [15848]

115. Saveland, James M.; Bunting, Stephen C. 1988. Fire effects in ponderosa pine forests. In: Baumgartner, David M.; Lotan, James E., compilers. Ponderosa pine: the species and its management: Symposium proceedings; 1987 September 29 - October 1; Spokane, WA. Pullman, WA: Washington State University, Cooperative Extension: 125-131. [9409]

116. Schroeder, Mark J.; Buck, Charles C. 1970. Fire weather...a guide for application of meteorological information to forest fire control operations. Agricultural Handbook 360. Washington, DC: U.S. Department of Agriculture, Forest Service. 229 p. [37423]

117. Schubert, Gilbert H. 1970. Ponderosa pine regeneration problems in the Southwest. In: Hermann, R. K., compiler. Regeneration of ponderosa pine: Proceedings of a symposium; 1969 September 11-12; [Location of conference unknown]. Corvallis, OR: Oregon State University, School of Forestry: 1-4. [16349]

118. Schubert, Gilbert H. 1974. Silviculture of southwestern ponderosa pine: the status of our knowledge. Res. Pap. RM-123. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 71 p. [10888]

119. Seklecki, Mariette T.; Grissino-Mayer, Henri D.; Swetnam, Thomas W. 1996. Fire history and the possible role of Apache-set fires in the Chiricahua Mountains of southeastern Arizona. In: Ffolliott, Peter F.; DeBano, Leonard F.; Baker, Malchus, B., Jr.; [and others], tech. coords. Effects of fire on Madrean Province ecosystems: a symposium proceedings; 1996 March 11-15; Tucson, AZ. Gen. Tech. Rep. RM-GTR-289. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 238-246. [28082]

120. Servis, Steve; Boucher, Paul F. 1999. Restoring fire to southwestern ecosystems: is it worth it? In: Gonzalez-Caban, Armando; Omi, Philip N., tech. coords. Proceedings of the symposium on fire economics, planning, and policy: bottom lines; 1999 April 5-9; San Diego, CA. Gen. Tech. Rep. PSW-GTR-173. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 247-253. [37051]

121. Shiflet, Thomas N., ed. 1994. Rangeland cover types of the United States. Denver, CO: Society for Range Management. 152 p. [23362]

122. Steele, Robert. 1988. Ecological relationships of ponderosa pine. In: Baumgartner, David M.; Lotan, James E., compilers. Ponderosa pine: The species and its management: Symposium proceedings; 1987 September 29 - October 1; Spokane, WA. Pullman, WA: Washington State University, Cooperative Extension: 71-76. [9402]

123. Stickney, Peter F. 1989. Seral origin of species originating in northern Rocky Mountain forests. Unpublished draft on file at: U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Fire Sciences Laboratory, Missoula, MT. 10 p. [20090]

124. Sutherland, Elaine Kennedy. 1989. The natural and unnatural fire history of Southwestern ponderosa pine. Women in Natural Resources. 11(1): 12-16. [11515]

125. Sutherland, Elaine Kennedy; Covington, W. Wallace; Andariese, Steve. 1991. A model of ponderosa pine growth response to prescribed burning. Forest Ecology and Management. 44(2-4): 161-173. [17662]

126. Swetnam, Thomas W.; Baisan, Christopher H. 1996. Historical fire regime patterns in the southwestern United States since AD 1700. In: Allen, Craig D., ed. Fire effects in Southwestern forests: Proceedings, 2nd La Mesa fire symposium; 1994 March 29-31; Los Alamos, NM. RM-GTR-286. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 11-32. [27281]

127. Swetnam, Thomas W.; Baisan, Christopher H.; Caprio, Anthony C.; Brown, Peter M. 1992. Fire history in a Mexican oak-pine woodland and adjacent montane conifer gallery forest in southeastern Arizona. In: Ffolliott, Peter F.; Gottfried, Gerald J.; Bennett, Duane A.; [and others], technical coordinators. Ecology and management of oak and associated woodlands: perspectives in the southwestern United States and northern Mexico: Proceedings; 1992 April 27-30; Sierra Vista, AZ. Gen. Tech. Rep. RM-218. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 165-173. [19759]

128. Swetnam, Thomas W.; Betancourt, Julio L. 1990. Fire-southern oscillation relations in the southwestern United States. Science. 249: 1017-1020. [12106]

129. Swetnam, Thomas W.; Betancout, Julio L. 1998. Mesoscale disturbance and ecological response to decadal climatic variability in the American Southwest. Journal of Climate. 11: 3128-3147. [37431]

130. Swetnam, Thomas W.; Dieterich, John H. 1985. Fire history of ponderosa pine forests in the Gila Wilderness, New Mexico. In: Lotan, James E.; Kilgore, Bruce M.; Fisher, William C.; Mutch, Robert W., technical coordinators. Proceedings, symposium and workshop on wilderness fire; 1983 November 15-18; Missoula, MT. General Technical Report INT-182. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station: 390-397. [7369]

131. Taylor, Walter P.; Gorsuch, D. M. 1932. A test of some rodent and bird influences on western yellow pine reproduction at Fort Valley, Flagstaff, Arizona. Journal of Mammalogy. 13(3): 218-223. [20354]

132. U.S. Department of Agriculture, National Resource Conservation Service. 2003. PLANTS database (2003), [Online]. Available: http://plants.usda.gov/. [34262]

133. Uresk, Daniel W.; Paintner, Wayne W. 1985. Cattle diets in a ponderosa pine forest in the northern Black Hills. Journal of Range Management. 38(5): 440-442. [2401]

134. Van Sickle, F. S.; Hickman, R. D. 1959. The effect of understory competition on the growth rate of ponderosa pine in north central Oregon. Journal of Forestry. 57: 852-853. [4608]

135. van Wagtendonk, Jan W. 1983. Prescribed fire effects on forest understory mortality. In: 7th conference: fire and forest meteorology: Proceedings; 1983 April 25-28; Fort Collins, CO. Boston, MA: American Meteorological Society: 136-138. [30327]

136. Veblen, Thomas T.; Kitzberger, Thomas; Donnegan, Joseph. 2000. Climatic and human influences on fire regimes in ponderosa pine forests in the Colorado Front Range. Ecological Applications. 10(4): 1178-1195. [35647]

137. Wagener, Willis W. 1955. Preliminary guidelines for estimating the survival of fire-damaged trees. Res. Note. No. 98. Berkeley, CA: U.S. Department of Agriculture, Forest Service, California [Pacific Southwest] Forest and Range Experiment Station. 9 p. [12345]

138. Wagener, Willis W. 1961. Guidelines for estimating the survival of fire-damaged trees in California. Misc. Paper 60. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station. 11 p. [4611]

139. Wasser, Clinton H. 1982. Ecology and culture of selected species useful in revegetating disturbed lands in the West. FWS/OBS-82/56. Washington, DC: U.S. Department of the Interior, Fish and Wildlife Service. 347 p. [4837]

140. Weaver, Harold. 1951. Fire as an ecological factor in the Southwestern ponderosa pine forests. Journal of Forestry. 49(2): 93-98. [37484]

141. Weaver, Harold. 1952. A preliminary report on prescribed burning in virgin ponderosa pine. Journal of Forestry. 50: 662-667. [18642]

142. White, Alan S. 1985. Presettlement regeneration patterns in a Southwestern ponderosa pine stand. Ecology. 66(2): 589-594. [4621]

143. Whittaker, R. H.; Niering, W. A. 1965. Vegetation of the Santa Catalina Mountains, Arizona: a gradient analysis of the south slope. Ecology. 46: 429-452. [9637]

144. Wright, Henry A.; Bailey, Arthur W. 1982. Fire ecology: United States and southern Canada. New York: John Wiley & Sons. 501 p. [2620]

145. Zwolinski, Malcolm J. 1996. Effects of fire on montane forest ecosystems. In: Ffolliott, Peter F.; DeBano, Leonard F.; Baker, Malchus, B., Jr.; [and others], tech. coords. Effects of fire on Madrean Province ecosystems: a symposium proceedings; 1996 March 11-15; Tucson, AZ. Gen. Tech. Rep. RM-GTR-289. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 55-63. [28062]




FEIS Home Page