Alligator juniper is the largest southwestern juniper, but most commonly grows as a medium-sized evergreen tree that reaches 20 to 40 feet (6.1-12.2 m) at maturity [82,139]. It can attain heights of up to 65 feet (20 m) and maximum diameters of 7 feet (2.1 m) [69, 85]. A single short but heavy massive trunk is more typical than multiple stems [10,103]. Alligator juniper has a "dense and spreading canopy of deep green foliage" [103]. The plant receives its name from the thick, checkered, furrowed bark which is divided into scales resembling the back of an alligator [62,103,139]. Mature alligator junipers often have a large portion of dead wood intermixed with living wood. Chojnacky [23] estimated dead wood at less than 15% total volume in alligator juniper.
Cones generally contain 3 to 5 seeds [125]. The hard, mealy "berries," which mature during the second year, are approximately ? inch (1.3 cm) in diameter [82].
Alligator juniper is noted for its slow growth rate. It ceases growth when moisture conditions are unfavorable but begins growing again with adequate moisture [54]. This characteristic greatly enhances the ability of alligator juniper to survive in harsh, arid environments. A diameter growth rate of approximately 0.6 inch (1.5 cm) per decade is typical for young trees, with growth slowing to 0.4 inch (0.1 cm) per decade after the tree reaches 170 years of age [90]. Maximum longevity is reported at 500 years [85].
Alligator juniper grows in semi-arid to subhumid montane "island" ecosystems in the Chihuahuan Desert and adjacent dry areas [37] as a subdominant in ponderosa pine forests of New Mexico, in riparian forest and riparian woodlands of Arizona [18,33]. Annual precipitation in pinyon-juniper ranges from 12 to 22 inches (305-559 mm) [49]. Alligator juniper is well adapted to survive short-term droughts, but mortality can occur after more than 6 years of drought [37]. Alligator juniper soils are variable but tend to be shallow, rocky and of low fertility [86]. Clay content averages approximately 18 to 27%. Some researchers report that alligator juniper favors soils which are slightly to moderately alkaline [81].
Alligator juniper most commonly grows between 4,000 and 6,000 ft (1,220-1,830 m) [30]. Elevational ranges of alligator juniper are as follows [46,82,86]:
4,426 to 7,915 ft (1,350-2,414 m) from AZ to NM
5,100 to 6,000 ft (1,556-1,830 m) from NM to TX
Alligator juniper begins annual leader elongation in the early spring when soil temperatures warm to approximately 50 degrees Fahrenheit (10oC) [54]. Phenological development in Arizona was as follows:
Phenological stage Date
bark begins to slip April 1
pollen shedding and female cones open April 8
approximate start of leader elongation April 20
1st conspicuous formation of male cones August 19
bark begins to stick September 15
leader elongation ceases October 19
Throughout its range, alligator juniper flowers from February through March [66,86]. Lymbery and Pieper [86] report the following phenological sequence in the Sacramento Mountains of New Mexico:
Year Month Stage of development
1 February-March cones open; pollen disperses
2 August-October cones mature; seed disperses
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".
Alligator juniper is monoecious. Cones open during February or March and mature from August to October of their second year [66]. Cone crop production exhibits significant annual variation [91].
Juniper seeds have low germination rates due to impermeable to semipermeable, thick, hard seedcoats, chemical inhibitors, and dormant embryos [56,64,106]. Juniper seeds remain dormant in the soil until favorable moisture conditions promote germination [64]. "Major episodes" of alligator juniper establishment can occur during wet years [37]. Germination varies from 16 to 45%, with an average of 16% of alligator juniper seeds retaining viability after 9 years [6,64,66,125]. Approximately 30% of all alligator juniper seed stored in a warehouse for 5 years germinated [64]. Two to 3 years may be required for germination [30]. Pack [106] found that high temperatures, alternating temperatures, repeated freezing and thawing, removal of the seedcoat, and application of hydrogen peroxide, dilute acids, carbon dioxide, or light had little influence on the germination of juniper seeds. Johnsen and Alexander [66] note that the most common treatment for alligator juniper seed involves cold stratification at 41 degrees Fahrenheit (5oC) for a period of 30 to 120 days.
Shrubs and trees often moderate harsh environmental conditions so juniper seedlings are commonly found beneath a canopy [56]. Animal dispersal is known to be extremely important in alligator juniper. Up to 95% of juniper reproduction may be attributed to birds on harsh New Mexico sites [44,108]. Digestive processes may encourage germination [9,39]. Juniper seed is dispersed by gravity, run-off, birds, or mammals including coyote, bighorn sheep, mice, rabbits, and livestock [19, 99,122]. Birds such as Bohemian waxwing, American robin, wild turkey, and jays disperse juniper seed. Brightly colored alligator juniper "berries" can be seen by birds at some distance and large quantities of this readily available food source may be consumed [9,41].
Alligator juniper is noted for its prolific sprouting ability [62]. This species is capable of sprouting from shallow roots, the root crown, or epicormic buds located along the branches or trunk [22,47,50,86,133]. Alligator juniper generally sprouts prolifically from dormant basal, root, or stem buds whenever the top is damaged, and consequently is not significantly reduced by most mechanical treatments. Sprouting often occurs after removal or death of the main trunk. Research indicates that younger trees sprout more readily than older plants [6] and that sprouting ability declines as stump diameters increases [47]. Alligator junipers 2 feet (0.6 m) or larger in diameter rarely sprout [6]. Jameson and Johnsen [62] report the following sprouting by stump diameter:
Succession and stand dynamics are poorly documented in evergreen woodlands in which alligator juniper occurs[77]. Pieper and others [110] note that "successional patterns where alligator juniper is a major potential component of the vegetation have not been determined." Climax alligator juniper stands have been reported on ridges and canyon rims [51]. In southwestern New Mexico, alligator juniper is considered a "minor climax species" [90]. However, this species has been included as a codominant indicator of climax vegetation in several habitat type classifications [73]. A generalized successional pathway for pinyon-juniper communities after fire has been described as follows [56]:
The currently accepted scientific name of alligator juniper is Juniperus deppeana Steud. (Cupressaceae) [70,72,84,129,137]. Varieties and forms of alligator juniper include [1,2,136]:
Juniperus deppeana var. deppeana
Juniperus deppeana var. pachyphloea (Torr.) Martinez
Juniperus deppeana var. patoniana (Martinez) T.A. Zanoni
Juniperus deppeana var. robusta Martinez
Juniperus deppeana var. zacatecensis Martinez
These varieties differ with respect to geographic distribution, bark and leaf morphology, and in the composition of volatile oils [1,2,3,136].
Alligator juniper hybridizes with oneseed juniper (J. monosperma) from central Mexico through the Southwest to southern Colorado [53,79]. Redberry juniper (J. pinchotii) is a stabilized hybrid of alligator juniper and oneseed juniper [89,129]. Alligator juniper also hybridizes with Rocky Mountain juniper (J. scopulorum) [53,54,124].
Juniperus deppeana (alligator juniper or checkerbark juniper) is a small to medium-sized tree reaching 10–15 metres (33–49 feet) in height. It is native to central and northern Mexico and the southwestern United States.
The tree reaches 10–15 metres (33–49 feet), rarely 25 m (82 ft), in height. The bark is usually very distinctive, unlike other junipers, hard, dark gray-brown, cracked into small square plates superficially resembling alligator skin; it is however sometimes like other junipers, with stringy vertical fissuring. The shoots are 1–1.5 millimetres (1⁄32–1⁄16 inch) in diameter. On juvenile specimens, the leaves are needle-like and 5–10 mm (3⁄16–3⁄8 in) long. The leaves are arranged in opposite decussate pairs or whorls of three; in adulthood they are scale-like, 1–2.5 mm (1⁄16–1⁄8 in) long (up to 5 mm) and 1–1.5 mm broad. The cones are berrylike, 7–15 mm (1⁄4–9⁄16 in) wide, green when young and maturing to orange-brown with a whitish waxy bloom,. These contain 2–6 seeds, which mature in about 18 months. The male cones are 4–6 mm (3⁄16–1⁄4 in) long, and shed their pollen in spring. The species is largely dioecious, producing cones of only one sex on each tree, but occasional trees are monoecious.
Close-up of juniper berries
There are five varieties, not accepted as distinct by all authorities:
Native American names include táscate and tláscal.
It is native to central and northern Mexico (from Oaxaca northward) and the southwestern United States (Arizona, New Mexico, western Texas). It grows at moderate altitudes of 750–2,700 m (2,460–8,860 ft) on dry soils.
The berrylike cones are eaten by birds and mammals.[2][3]
Berries from alligator juniper growing in the Davis Mountains of West Texas are used to flavor gin, including one produced by WildGins Co. in Austin, Texas.[4]
Juniperus deppeana (alligator juniper or checkerbark juniper) is a small to medium-sized tree reaching 10–15 metres (33–49 feet) in height. It is native to central and northern Mexico and the southwestern United States.