Chihuahua White Pine

In the northern part of the range, Pinus strobiformis overlaps P . flexilis and reportedly hybridizes with it. On average P . strobiformis has longer, more slender leaves and thinner, more spreading-tipped apophyses than are found in P . flexilis , and stomatal bands are not evident on the abaxial surface of its leaves.

Trees to 30m; trunk to 0.9m diam., slender, straight; crown conic, becoming rounded to irregular. Bark gray, aging red-brown, furrowed, with narrow, irregular, scaly ridges. Branches spreading-ascending; twigs slender, pale red-brown, puberulous or glabrous, sometimes glaucous, aging gray or gray-brown, smooth. Buds ellipsoid, red-brown, ca. 1cm, resinous. Leaves 5 per fascicle, spreading to ascending-upcurved, persisting 3--5 years, 4--9cm ´ 0.6--1mm, straight, slightly twisted, pliant, dark green to blue-green, abaxial surface without evident stomatal lines, adaxial surfaces conspicuously whitened by narrow stomatal lines, margins sharp, razorlike and entire to finely serrulate, apex narrowly acute to short-subulate; sheath 1.5--2cm, shed early. Pollen cones cylindric, ca. 6--10mm, pale yellow-brown. Seed cones maturing in 2 years, shedding seeds and falling soon thereafter, pendent, symmetric, lance-cylindric before opening, broadly lance-cylindric when open, 15--25cm, creamy brown to light yellow-brown, stalks to 6cm; apophyses somewhat thickened, strongly cross-keeled, tip reflexed; umbo terminal, low. Seeds ovoid; body 10--13mm, red-brown, essentially wingless. 2 n =24.

Arid to moist summit elevations, montane forests; 1900--3000m; Ariz., N.Mex., Tex.; n Mexico.

Pinus ayacahuite Ehrenberg var. brachyptera G.R. Shaw; P. ayacahuite var. reflexa (Engelmann) Voss; P. ayacahuite var. strobiformis (Engelmann) Lemmon; P. flexilis E.James var. reflexa Engelmann; P. reflexa (Engelmann) Engelmann

southwestern white pine
border white pine
pino enano

More info for the term: dehiscent

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].

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].

More info for the terms: fire regime, frequency, seed

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].

FIRE REGIMES :
Find fire regime information for the plant communities in which this
species may occur by entering the species name in the FEIS home page under
"Find FIRE REGIMES".

More info for the terms: fuel, natural, prescribed fire, series

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].

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More info for the term: phanerophyte

Phanerophyte

More info for the terms: forest, mesic, shrubs, tree

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].

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This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):

   206  Engelmann spruce - subalpine fir
   210  Interior Douglas-fir
   211  White fir
   216  Blue spruce
   217  Aspen
   219  Limber pine
   237  Interior ponderosa pine

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This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):

   FRES21  Ponderosa pine
   FRES23  Fir - spruce

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This species is known to occur in association with the following plant community types (as classified by Küchler 1964):

More info for the term: forest

   K018  Pine - Douglas-fir forest
   K019  Arizona pine forest
   K020  Spruce - fir - Douglas-fir forest
   K021  Southwestern spruce - fir forest

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.

More info for the terms: forest, natural

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].

More info for the terms: forest, habitat type, series, woodland

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].

More info for the term: tree

Tree

More info for the terms: basal area, density, forest, seed, seed tree, tree

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 less than 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].

     AZ  CO  NM  TX  MEXICO

Southwestern white pine is grown as an ornamental [73,78].

Southwestern white pine seeds are palatable to small mammals and birds
[11,34].

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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].

More info for the term: tree

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].

More info for the terms: root crown, secondary colonizer, tree

   Tree without adventitious-bud root crown
   Secondary colonizer - off-site seed

More info for the terms: forest, seed, stratification, tree

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 less than 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].

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This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):

    7  Lower Basin and Range
   11  Southern Rocky Mountains
   12  Colorado Plateau
   13  Rocky Mountain Piedmont

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More info for the terms: climax, codominant, tree

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.

Pinus reflexa Engelm.
Pinus ayacahuite var. strobiformis Lemmon

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].

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].

Tree, Evergreen, Monoecious, Habit erect, Trees without or rarely having knees, Tree with bark rough or scaly, Young shoots 3-dimensional, Buds resinous, Leaves needle-like, Leaves alternate, Needle-like leaf margins entire (use magnification), Leaf apex acute, Leaves < 5 cm long, Leaves > 5 cm long, Leaves < 10 cm long, Leaves blue-green, Leaves not blue-green, Leaves white-striped, Needle-like leaves triangular, Needle-like leaves not twisted, Needle-like leaf habit drooping, Needle-like leaves per fascicle mostly 5, Needle-like leaf sheath early deciduous, Twigs glabrous, Twigs pubescent, Twigs viscid, Twigs not viscid, Twigs without peg-like projections or large fascicles after needles fall, Berry-like cones orange, Woody seed cones > 5 cm long, Seed cones bearing a scarlike umbo, Umbo with obvious prickle, Bracts of seed cone included, Seeds red, Seeds brown, Seeds wingless, Seed wings narrower than body.

Pinus strobiformis, commonly known as southwestern white pine, Mexican white pine or Chihuahua white pine, is a medium-sized white pine tree whose native habitat is in southwestern United States and Mexico. It is typically a high-elevation pine growing mixed with other conifers (a montane forest).