SPECIES: Pinus strobiformis
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INTRODUCTORY


AUTHORSHIP AND CITATION : Pavek, Diane S. 1993. Pinus strobiformis. 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 : PINSTO SYNONYMS : Pinus reflexa Engelm. Pinus ayacahuite var. strobiformis Lemmon SCS PLANT CODE : PIST3 COMMON NAMES : southwestern white pine Mexican white pine border white pine pino enano TAXONOMY : The currently accepted scientific name of southwestern white pine is Pinus strobiformis Engelm. [6]. There are no recognized subspecies, varieties, or forms. Southwestern white pine hybridizes with limber pine (P. flexilis James) where their ranges overlap [6,17,53]. LIFE FORM : Tree FEDERAL LEGAL STATUS : No special status OTHER STATUS : NO-ENTRY

DISTRIBUTION AND OCCURRENCE

SPECIES: Pinus strobiformis
GENERAL DISTRIBUTION : Southwestern white pine has a limited distribution.  It is found in the mountains of western Texas, New Mexico, Arizona, and southwestern Colorado [15,16,50].  It extends south along the mountains to central Mexico; most of its distribution is in Mexico [44,50,65]. ECOSYSTEMS :    FRES21  Ponderosa pine    FRES23  Fir - spruce STATES :      AZ  CO  NM  TX  MEXICO BLM PHYSIOGRAPHIC REGIONS :     7  Lower Basin and Range    11  Southern Rocky Mountains    12  Colorado Plateau    13  Rocky Mountain Piedmont KUCHLER PLANT ASSOCIATIONS :    K018  Pine - Douglas-fir forest    K019  Arizona pine forest    K020  Spruce - fir - Douglas-fir forest    K021  Southwestern spruce - fir forest SAF COVER TYPES :    206  Engelmann spruce - subalpine fir    210  Interior Douglas-fir    211  White fir    216  Blue spruce    217  Aspen    219  Limber pine    237  Interior ponderosa pine SRM (RANGELAND) COVER TYPES : NO-ENTRY HABITAT TYPES AND PLANT COMMUNITIES : Southwestern white pine normally occurs in low densities in southwestern pine, mixed-conifer, and spruce-fir forests [67].  It occurs as an associate in habitat type series of the major conifers in these forests [3,4,5,17,26,52].  Southwestern white pine infrequently forms small pure stands; it is most likely to be dominant in high-elevation, cool habitats [49,51,53]. Southwestern white pine may be present as a minor component in riparian community types in south-central Arizona and in the montane riparian woodland zone of southwestern Colorado [9,70]. Southwestern white pine is listed as an indicator species in the following publications: (1)  Classification of the forest vegetation on the National Forests of        Arizona and New Mexico [5] (2)  A classification of forest habitat types of northern New Mexico and        southern Colorado [18] (3)  Forest habitat types in the Apache, Gila, and part of the Cibola        National Forests, Arizona and New Mexico [26] (4)  Forest and woodland habitat types (plant associations) of northern        New Mexico and northern Arizona [49] (5)  A classification of spruce-fir and mixed conifer habitat types of        Arizona and New Mexico [51].

MANAGEMENT CONSIDERATIONS

SPECIES: Pinus strobiformis
WOOD PRODUCTS VALUE : Southwestern white pine wood is soft, not resinous, and white with a slightly darker heartwood.  It is used locally for cabinetry, doors, and window frames [53].  Crooked stems and coarse branches make it undesirable for lumber [41]. IMPORTANCE TO LIVESTOCK AND WILDLIFE : Seeds of southwestern white pine are eaten by small mammals and birds. It is not generally browsed by game animals or livestock [41]. Southwestern white pine was seldom used by birds in either logged or unlogged forest areas [27]. Southwestern white pine is often found in mixed-conifer forests that are valuable summer habitat for big and small game animals, rodents, and game and nongame birds [19,25].  Since natural regeneration of clearcut mixed-conifer forests on south-facing slopes requires 50 to 100 years, these clearcut areas can be a valuable long-term forage resource for deer and elk [71]. PALATABILITY : Southwestern white pine seeds are palatable to small mammals and birds [11,34]. NUTRITIONAL VALUE : NO-ENTRY COVER VALUE : NO-ENTRY VALUE FOR REHABILITATION OF DISTURBED SITES : NO-ENTRY OTHER USES AND VALUES : Southwestern white pine is grown as an ornamental [73,78]. OTHER MANAGEMENT CONSIDERATIONS : Silviculture:  Various silviculture systems have been used in the mixed-conifer forests where southwestern white pine occurs.  The average annual growth of southwestern white pine was less than 0.1 inch (0.25 cm) per year in a virgin mixed-conifer stand in Arizona.  The initial volume of southwestern white pine was 1,097 board feet per acre, and after 5 years, the volume was 1,163 board feet per acre [30]. Small patch clearcutting has been used for regeneration of southwestern white pine and associated conifers in old-growth mixed-conifer stands [24,32].  Regeneration density of southwestern white pine per acre was low after 10 years [24]. Gray [33] classified southwestern white pine as a suitable seed tree. Southwestern white pine regeneration by seed trees was not successful, however, in communities at 9,500 to 10,000 feet (2,896-3,048 m); revegetation was very slow [49]. Spot seeding yielded a low number of surviving southwestern white pine seedlings in east-central Arizona [39,43].  Rodents were controlled, but frost heaving and unsuitable tree ecotypes could have factored into the seedling mortality [39].  Heavy broadcast seeding of southwestern white pine should be used instead of spot seeding [43]. Planting southwestern white pine seedlings at different elevations and densities are discussed in detail [41]. Wildlife:  Patch clearcuts were evaluated for forage production and utilization by ungulates.  Understory production significantly (p<0.05) increased on clearcut areas; however, utilization by ungulates did not differ significantly (p>0.05) [23].  Equations are available for predicting forage production in mixed-conifer forests [22,48].  Patch clearcuts removed about 30 percent of the total basal area in an uneven- aged virgin Arizona mixed-conifer forest, which did not adversely affect the nesting or feeding of birds [62].  This method reduced southwestern white pine basal area by 47 percent on northern aspects and by 13 percent on southern aspects. Some of the mixed-conifer forests that southwestern white pine is in provide habitat for sensitive and threatened species such as Mexican spotted owl, northern goshawk, and Sacramento Mountain salamander [28,56,61]. Damaging agents:  Southwestern white pine is the principal host of Apache dwarf mistletoe (Arceuthobium apachecum).  Infected trees have reduced growth, increased susceptibity to other infections, insects, and mortality [35,75].  Southwestern white pine is infected by red ring rot and by root and butt rots [75].  Southwestern white pine seedlings received an average overall ranking of 8.8 in trials for resistance to white pine blister rust; a score of 11 was the lowest resistance [38]. Other factors:  Various methods of weed suppression made no significant (p=0.10) difference in growth of southwestern white pine produced in containers [7]. Southwestern white pine has good potential for Christmas tree production in the eastern United States [36,78]. Southwestern white pine is planted along streets in urban areas.  Its foliage has an intermediate susceptibility to salt spray; medium foliar injury with moderate growth reduction occurred [73].

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Pinus strobiformis
GENERAL BOTANICAL CHARACTERISTICS :  
Southwestern white pine is a native, evergreen conifer with an open,
irregular crown.  It can grow to 90 feet (27 m) tall with diameters to
3.2 feet (1 m) [15,53,64].  The bark is thin, rough, and furrowed
[15,54].  Branches are long and horizontal to pendant [53].  Needles 
are 2.4 to 4 inches (6-10 cm) long in fascicles of five [53].  The cones 
are 2.8 to 9.8 inches (7-25 cm) long with reflexed, thick scales; cones 
are dehiscent when mature [15,46].  Seeds are essentially wingless and 0.4
to 0.5 inch (10-12 mm) long [15,53].

RAUNKIAER LIFE FORM : 
Phanerophyte

REGENERATION PROCESSES : 
Southwestern white pine reproduces sexually.  It begins to produce cones
when pole sized or about 15 years [39,44].  The interval between seed
crops for any one tree is 3 to 4 years [44].  Seed traps were placed in
clearcut mixed-conifer forest in Arizona to monitor regeneration over 3
years.  No southwestern white pine seeds were found in the traps [39].

Southwestern white pine seeds require 2 weeks to 4 months stratification
before germinating [43,44,78].  Germinability can vary between 52 and 95
percent [43,44].  Seed collection and germination methods are discussed
in detail [36,44].

Seeds of the southwestern white pine ripen synchronously throughout a
forest and overwhelm the harvesting efforts of predators [11,34].  Red
squirrels clip entire cones and cache them [34].  The wingless seeds are
dispersed by birds, primarily by the Steller's jay and Clark's
nutcracker [11,47,72].  Animal caches result in clustered stands [72].

Southwestern white pine seedlings root deeply (to about 8 inches [20.3
cm]) the first year, which increases their survival under drought
conditions [40,43].  All of the southwestern white pine seedlings died
in a greenhouse experiment that assessed the drought resistance of
conifers along an elevational gradient.  Southwestern white pine died
after significantly (p<0.05) fewer days than other conifer species from
lower elevations [10].

With the initial deep root growth, southwestern white pine seedlings had
the slowest top growth rate of four conifer species measured.  At about
6 years of age, the average height of southwestern white pine seedlings
was 13.3 inches (33.8 cm) [40].  In another study, 2-year-old seedlings
were between 4 and 8 inches (10.2-20.3 cm) tall [36].

SITE CHARACTERISTICS : 
Southwestern white pine is widespread in mesic sites on ridges, slopes,
and canyons of montane zones [15].  The best growth of this species
occurs on moist, cool sites with deep soil [14,53].  The climate is
semiarid, characterized by mild winters and warm summers.  There are two
wet seasons:  July to September and December to March [2,10].  Average
precipitation ranges from 19.2 to 45 inches (487-1,143 mm) per year
[25,27,57].

Southwestern white pine occurs in ravines or on mesic lower slopes at
5,000 feet (1,525 m) in southeastern Arizona and goes up to timberline
in southwestern Colorado [52,76].  It is typically found at elevations
from 6,000 to 10,000 feet (1,830-3,048 m) [17,52].  Southwestern white
pine often occurs on north- to east-facing slopes, but it has been
reported on all aspects [1,11,17,57,71].

Southwestern white pine is found on sites with loamy soil textures
ranging from shallow, gravelly loams to deep, sandy loams to stony
silty clay loams [23,30,32,40].

Two to nine conifer species occur in the southwestern mixed-conifer
forest type.  Their proportions vary depending on site characteristics
[37,48].  Some associated species not mentioned in Distribution and
Occurrence are listed below.  Associated tree species are New Mexico
locust (Robinia neomexicana), Gambel oak (Quercus gambelii), and
silverleaf oak (Quercus hypoleucoides) [14].  Associated shrubs are
mountain snowberry (Symphoricarpos oreophilus), bush oceanspray
(Holodiscus dumosus), Arizona honeysuckle (Lonicera arizonica), and
Fendler ceanothus (Ceanothus fendleri) [8,14,23,57].  Other associated
plants are Arizona fescue (Festuca arizonica), screwleaf muhly
(Muhlenbergia virescens), pine dropseed (Blepharoneuron tricholepsis),
Arizona wheatgrass (Elymus arizonicus), and western yarrow (Achillea
lanulosa) [8,23,51].

SUCCESSIONAL STATUS : 
Southwestern white pine is frequently a persistent, long-lived seral or
climax species in mixed-conifer forests [4,26,51].  It has been
classified as an early successional major tree [60].  Southwestern white
pine infrequently is a climax dominant or codominant in open stands
[4,51,69].

Southwestern white pine is relatively shade intolerant compared to other
associated conifers in the southwestern mixed-conifer forests.  It is
relatively resistant to damage from full sunlight [41].  In 8 out of 12
sites in New Mexico, southwestern white pine was in the overstory, but
in only 2 of those 12 sites was it in the understory.  Ahlstrand [1]
suggested that canopy closure prevented southwestern white pine
replacement at these sites.

SEASONAL DEVELOPMENT : 
Southwestern white pine flowers in June.  Cones mature in September, and
seeds are dispersed from September to October [44].  Southwestern white
pine seeds germinate either in the spring or in the summer after the
rains begin [40].


FIRE ECOLOGY

SPECIES: Pinus strobiformis
FIRE ECOLOGY OR ADAPTATIONS : Southwestern white pine is not fire adapted; it does not have fire-induced sprouting, seed germination, or biomass increases [12]. Southwestern white pine is fire sensitive in young age classes.  Older trees with somewhat thicker bark are relatively more fire resistant [20].  The thin bark and horizontal or drooping branches increase its susceptibility to fire. Lightning-ignited fires occur in the southwestern forests during spring or early summer before the rains begin [2].  Arizona and New Mexico mixed-conifer forests have the highest frequency of lightning fires in the United States [77]. Fire-scarred cross sections of living and dead southwestern white pine and other conifers were examined to determine the role of fire in southwestern forests.  Over time spans of 288 and 426 years, the average intervals between fires in western Texas and east-central Arizona were 4.7 to 9 or 22 years [2,8,20].  These chronologies have been used with climatic data to develop fire hazard forecasting models [68]. POSTFIRE REGENERATION STRATEGY :    Tree without adventitious-bud root crown    Secondary colonizer - off-site seed

FIRE EFFECTS

SPECIES: Pinus strobiformis
IMMEDIATE FIRE EFFECT ON PLANT : Fire damaged stems of young (less than 15 years) southwestern white pine usually die; older trees (more than 50 years) are susceptible to scarring [2]. No information was found in the literature about the fire susceptibility of southwestern white pine seeds stored in caches.  It is possible that soil may sufficiently insulate cached seeds from fire damage. DISCUSSION AND QUALIFICATION OF FIRE EFFECT : NO-ENTRY PLANT RESPONSE TO FIRE : Southwestern  white pine may establish after fire through bird-dispersed seeds. While southwestern white pine is known to be an important seral tree following fire, such as in white fir-Douglas-fir (Abies concolor- Pseudotsuga menziesii)/Gambel oak habitat types, no information was found in the literature about southwestern white pine rates of recovery after fire [51]. DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : NO-ENTRY FIRE MANAGEMENT CONSIDERATIONS : Prediction of natural fuel loadings in southwestern mixed-conifer forests is difficult; much variation exists within and between stands [58].  Sackett [59] reported average square diameter and specific gravity for southwestern white pine and other conifers in different size classes, making the planar intersect method of fuel evaluation applicable to southwestern forests. Regeneration by prescribed fire of mixed-conifer series for wildlife has been discussed in detail [63].

REFERENCES

SPECIES: Pinus strobiformis
REFERENCES :  1.  Ahlstrand, Gary M. 1979. Preliminary report on the ecology of fire        study, Guadalupe Mountains and Carlsbad Caverns National Parks. In:        Genoways, Hugh H.; Baker, Robert J., eds. Biological investigations in        the Guadalupe Mountains National Park: Proceedings of a symposium; 1975        April 4-5; Lubbock, TX. Proceedings and Transactions Series No. 4.        Washington, DC: U.S. Department of the Interior, National Park Service:        31-44.  [16015]  2.  Ahlstrand, Gary M. 1980. Fire history of a mixed conifer forest in        Guadalupe Mountains National Park. In: Stokes, Marvin A.; Dieterich,        John H., technical coordinators. Proceedings of the fire history        workshop; 1980 October 20-24; Tucson, AZ. Gen. Tech. Rep. RM-81. Fort        Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky        Mountain Forest and Range Experiment Station: 4-7.  [16035]  3.  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]  4.  Alexander, Billy G., Jr.; Ronco, Frank, Jr.; White, Alan S.; Ludwig,        John A. 1984. Douglas-fir habitat types of northern Arizona. Gen. Tech.        Rep. RM-108. Fort Collins, CO: U.S. Department of Agriculture, Forest        Service, Rocky Mountain Forest and Range Experiment Station. 13 p.        [301]  5.  Alexander, Robert R.; Ronco, Frank, Jr. 1987. Classification of the        forest vegetation on the National Forests of Arizona and New Mexico.        Res. Note RM-469. Fort Collins, CO: U.S. Department of Agriculture,        Forest Service, Rocky Mountain Forest and Range Experiment Station. 10        p.  [3515]  6.  Andresen, John W.; Steinhoff, Raphael J. 1971. The taxonomy of Pinus        flexilis and P. strobiformis. Phytologia. 22(2): 57-70.  [332]  7.  Appleton, Bonnie L.; Derr, Jeffrey F. 1990. Use of geotextile disks for        container weed control. HortScience. 25(6): 666-668.  [20642]  8.  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]  9.  Baker, William L. 1988. Size-class structure of contiguous riparian        woodlands along a Rocky Mountain river. Physical Geography. 9(1): 1-14.        [9269] 10.  Barton, Andrew M. 1992. Factors controlling lower elevational limits of        plants: responses of pines to drought in the Chiricahua Mountains,        Arizona. In: Ffolliott, Peter F.; Gottfried, Gerald J.; Bennett, Duane        A.; [and others], technical coordinators. 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In: Scharpf, Robert F.; Parmeter, John R., Jr.,        technical coordinators. Proceedings of the symposium on dwarf mistletoe        control through forest management; 1978 April 11-13; Berkeley, CA. Gen.        Tech. Rep. PSW-31. Berkeley, CA: U.S. Department of Agriculture, Forest        Service, Pacific Southwest Forest and Range Experiment Station: 5-15.        [14249] 36.  Heit, C. E. 1973. Propagation from seed. Part 24. Testing and growing        limber and Mexican border pines. American Nurseryman. 137: 8-9; 64-74.        [20643] 37.  Hermann, Richard K.; Lavender, Denis P. 1990. Pseudotsuga menziesii        (Mirb.) Franco  Douglas-fir. 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: 527-540.  [13413] 38.  Hoff, R.; Bingham, R. T.; McDonald, G. I. 1980. Relative blister rust        resistance of white pines. 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