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photograph

At left, P. arizonica var. arizonica along Mex-16 near the Chihuahua-Sonora border. At right, P. leiophylla var. chihuahuana [C.J. Earle, 2007.02.08].

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Mature tree of var. cooperi, 12 m tall [C.J. Earle, 2007.02.10].

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Tree of var. stormiae, approx. 10 m tall, on Cerro Potosí (at 24.893°N, 100.218°W) [C.J. Earle, 2007.02.19].

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Left: Needles and cone of P. arizonica from lower slopes of Mt. Lemmon, Arizona. Right: Needles and cone of P. ponderosa from upper slopes of Mt. Lemmon [Jeff Bisbee].

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Foliar units on a tree in the Santa Rita Mtns., Arizona [C.J. Earle 2012.12.28].

 

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Conservation status

Pinus arizonica

Engelmann ex Rothrock 1878

Common names

Arizona pine; pino de Arizona [Spanish].

Taxonomic notes

Three varieties: arizonica, cooperi, and stormiae.

"Engelmann (Rothrock 1878) stressed the difference in leaf number with P. ponderosa (5 vs. 3), but found it otherwise very similar to certain forms of that species. Shaw (1909, 1914) reduced it to a variety of P. ponderosa when it became known that the 'leaf-fascicles (are) heteromerous, with the larger number in the southern parts of its range (referring to P. ponderosa s.l.)... P. arizonica has often been treated under [P. ponderosa] as a variety, but more recent treatments recognize it as a distinct species, with possible introgression in Arizona and New Mexico" (Farjon & Styles 1997).

Description

Trees to 35 m tall with a straight, massive trunk up to 120 cm in diameter. Crown open, pyramidal in young trees, becaming round-topped; branches thick and spreading, the first-order branches drooping and the others ascending. Bark on young trees dark brown, rough and scaly, with age becoming 4-5 cm thick, deeply furrowed, divided into large irregular plates separating into thin closely appressed light cinnamon-brown scales. Twigs first orange-brown, pruinose, later turning dark gray-brown, with decurrent leaf bract scales. Needles tufted at the ends of the branches, in fascicles of 3-5 needles, 12-22 cm long, thick, rigid, dark green, with stomata on all sides; margins finely serrate; resin canals 6-10, medial, and with two distinct vascular bundles; fascicle sheaths brown, persistent, initially to 30 mm long but wearing shorter, turning dark gray; needles falling after 2-3 seasons. Cotyledons 7-9. Seed cones ovoid to conical, symmetrical, 6-9 cm long, borne in groups of 1-3 on short, stout peduncles, light red-brown at maturity, with hard, stiff scales 12-14 mm wide, the apex margin rounded and smoothed with apophyses raised and with a transverse keel; armed with slender recurved spines. Cones open at maturity and are soon deciduous, leaving the peduncle and a few basal cone scales attached to the branchlet. Pollen cones borne in dense clusters at the ends of new shoots, 15-20×5 mm, yellow to yellow-brown. Seeds dark brown, 6 mm long, oval, slightly compressed towards the apex, with a thick coat; seed wings articulate, 20-25×8-9 mm, with about 28,000 seeds/kg. Wood light, soft, brittle, light red or yellow, with thick pale yellow or white sapwood (Sargent 1922, Perry 1991, Farjon and Styles 1997).

P. arizonica is often confused with P. ponderosa subsp. scopulorum in Arizona south of the Mogollon Rim, where the two species occur together and some introgression has been observed. Distinguishing characters include leaf number (2-4 in P. ponderosa and 3-5 in P. arizonica), number of resin canals (2-6 in P. ponderosa and 6-10 in P. arizonica), and cone scales (large strong erect prickles in P. ponderosa and small recurved prickles in P. arizonica) (Perry 1991).

Key to the varieties (Farjon & Styles 1997):

1. Leaves long (14-25 cm), thick (1.4-1.8 mm), with 8-12 lines of stomata on the abaxial side, 34(-5) per fascicle. var. stormiae
1. Leaves short or variable, <1.4(-1.6) mm thick.
2. Leaves variable in length (8-)10-20(-23) cm, in fascicles of 3-5, predominantly 3-4. var. arizonica
2. Leaves short, (5-)6-10(-12) cm, in fascicles of (3-)4-5, predominantly 5. var. cooperi

Distribution and Ecology

Distribution data. Pinus arizonica (undifferentiated) shown in red, var. arizonica shown in orange, var. cooperi shown in yellow, and var. stormiae shown in blue. Data sources (click on data points to view) include my observations, Farjon & Styles (1997), and downloads from GBIF (2014) and SEINet (2014).

USA: Mountains of southeast Arizona and southwest New Mexico at elevations of 1,800-2,450 m (Sargent 1922), with var. stormiae also found in some west Texas mountains (Perry 1991). Hardy to Zone 8 (cold hardiness limit between -12.1°C and -6.7°C) (Bannister and Neuner 2001); this is probably only in reference to the type variety.

Mexico: Mountains of the Sierra Madre Occidental in northeast Sonora, west Chihuahua, east Sinaloa, and Durango, at elevations of 2,000-2,800 m. Var. stormiae is also found in Coahuila, Nuevo León, southwest Tamaulipas (Miquihuana) and parts of San Luis Potosí (Perry 1991). The type variety and var. cooperi may form pure stands, but usually are mixed with other pines, junipers (J. flaccida at lower elevations, J. deppeana at higher), or species of Quercus. Var. stormiae typically occupies similar but drier sites, commonly with juniper or piñons such as P. cembroides (Farjon & Styles 1997).

Formerly extensive forests have been much reduced by logging, leaving a highly fragmented distribution (Perry 1991).

Big tree

See var. arizonica.

Oldest

Work by Barton et al. (2001), presumably using living trees, has identified fire events going back to 1610. Thus trees 400 years or older probably occur.

Dendrochronology

The species has seen little use, and what work has been done appears to have all used var. arizonica. Studies to date (late 2007) include some stable isotope work and a stand dynamics study by Barton et al. (2001), done in the Chiricahua Mountains.

Ethnobotany

The trees are harvested with associated pine species for construction lumber (Perry 1991).

Observations

See the varietal accounts.

Remarks

Citations

Barton, A.M., T.W. Swetnam, and C.H. Baisan. 2001. Arizona pine (Pinus arizonica) stand dynamics: local and regional factors in a fire-prone madrean gallery forest of Southeast Arizona, USA. Landscape Ecology 16(4): 351-369.

Rothrock, J.T. 1878. Reports upon the botanical collections made in portions of Nevada, Utah, California, Colorado, New Mexico and Arizona during the years 1871, 1872, 1873, 1874, and 1875 (Washington: Government Printing Office), Vol. 6, Botany: p. 260. Available at the Biodiversity Heritage Library, accessed 2011.03.20.

See also

Last Modified 2014-12-11