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SPECIES: Juniperus deppeana
Tirmenstein, D. 1999. Juniperus deppeana. In: Fire Effects Information System, [Online].
U.S. Department of Agriculture, Forest Service,
Rocky Mountain Research Station, Fire Sciences Laboratory (Producer).
Available: https://www.fs.usda.gov/database/feis/plants/tree/jundep/all.html/ [].
JUNDEP
SYNONYMS:Juniperus deppeana E. Von Steudal var. sperryi D. Correll [70]
NRCS PLANT CODE:JUDE2
COMMON NAMES:
alligator juniper
checker-bark juniper
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].
tree
FEDERAL LEGAL STATUS:No special status
OTHER STATUS:No entry
GENERAL DISTRIBUTION:
Alligator juniper occurs from western Texas to northwestern New Mexico and reaches its northern limit in north-central Arizona near Flagstaff. It extends southward into northern and central Mexico where it is described as "widespread" [37,79,80,82,84,125]. Distribution of varieties is as follows [138]:
| Juniperus deppeana var. deppeana | Sierra Madre Oriental in the state of Mexico north to Coahuila |
| J. d. var. robusta | Sierra Madre Occidental in the states of Zacatecas, Durango and Chihuahua |
| J. d. var. zacatecensis | western Mexico and adjacent Durango |
ECOSYSTEMS:
FRES21 Ponderosa pine
FRES28 Western hardwoods
FRES29 Sagebrush
FRES32 Texas savanna
FRES34 Chaparral-mountain shrub
FRES35 Pinyon-juniper
FRES36 Mountain grasslands
FRES37 Mountain meadows
STATES:
AZ CO NM TX MEXICO
BLM PHYSIOGRAPHIC REGIONS:
7 Lower Basin and Range
12 Colorado Plateau
13 Rocky Mountain Piedmont
KUCHLER PLANT ASSOCIATIONS:
K011 Western ponderosa forest
K023 Juniper-pinyon woodland
K031 Oak-juniper woodlands
SAF COVER TYPES:
237 Interior ponderosa pine
239 Pinyon-juniper
240 Arizona cypress
241 Western live oak
SRM (RANGELAND) COVER TYPES:
503 Arizona chaparral
504 Juniper-pinyon pine woodland
509 Transition between oak-juniper woodland and mahogany-oak association
733 Juniper-oak
HABITAT TYPES AND PLANT COMMUNITIES:
Alligator juniper occurs in pinyon-juniper (Pinus-Juniperus spp.), pine-oak (Pinus-Quercus spp.), juniper-oak, Madrean evergreen, and riparian woodlands, and in ponderosa pine (P. ponderosa) forest. It rarely grows in dense stands. Typically, it occurs in small groves or as individuals interspersed with other junipers, ponderosa pine, oaks, or various understory species [6,86,103]. Alligator juniper is a common component of pinyon-juniper woodlands with pinyon (P. edulis) and/or singleleaf pinyon (P. monophylla). It occurs at somewhat higher elevations than oneseed or Utah juniper [26,72,86]. Pinyon-juniper woodlands make up more than one half of New Mexico's forested lands, and alligator juniper represents approximately 7% of all trees within that area [24].
Alligator juniper also occurs in pine-oak woodlands of Arizona. Along with Mexican pinyon (P. cembroides) [31], it is an important constituent of juniper-oak woodlands of the Colorado Plateau [139]. In parts of southern Arizona and Mexico, it occurs in Madrean evergreen woodlands with various oaks and pines and in lower elevation, pygmy conifer-oak woodlands [10,84,122,126,]. These woodlands are characterized by having less oneseed juniper, Rocky Mountain juniper, and pinyon, but greater amounts of alligator juniper, Emory oak (Q. emoryi), gray oak (Q. grisea), Arizona white oak (Q. arizonica), and Mexican pinyon [20].
Tree species commonly codominating with alligator juniper include pinyon, oneseed juniper, ponderosa pine, and gray oak. Common shrub associates include skunkbush sumac (Rhus trilobata), true mountain-mahogany (Cercocarpus montanus), desert ceanothus (Ceanothus greggii), pointleaf manzanita (Arctostaphylos pungens), Apache plume (Fallugia paradoxa), and Parry agave (Agave parryi). Blue grama (Bouteloua gracilis), sideoats grama (B. curtipendula), vine-mesquite (Panicum obtusum), wolftail (Lycurus phleoides), bottlebrush squirreltail (Elymus elymoides), mountain muhly (Muhlenbergia montana), pine muhly (M. dubia), and bullgrass (M. emersleyi) are frequent grass associates of alligator juniper [11,73,96,109].
Alligator juniper is named as a dominant or indicator species in several pinyon-juniper and montane forest vegetation classifications. Publications describing plant communities dominated by alligator juniper are listed below.
Forest and woodland habitat types (plant associations) of Arizona south of the Mogollon Rim and southwestern New Mexico [11]
Ecology and diversity of pinon-juniper woodland in New Mexico [33]
A vegetation classification system for New Mexico, USA [36]
Ecology and classification of the pinyon-juniper woodlands in western New Mexico [55]
Plant associations of Region Two: Potential plant communities of Wyoming, South Dakota, Nebraska, Colorado, and Kansas [68]
Woodland classification: the pinyon-juniper formation [69]
A habitat type classification of the pinyon-juniper woodlands of the Lincoln National Forest, New Mexico [73]
Woodland communities and soils of Fort Bayard, southwestern New Mexico [90]
Classification of pinyon-juniper (P-J) sites on National Forests in the Southwest [96]
Spatial variation of pinon-juniper woodlands in New Mexico [109]
Plant associations (habitat types) of the forests and woodlands of Arizona and New Mexico [123]
WOOD PRODUCTS VALUE:
Wood of alligator juniper currently has little commercial value. Springfield [120] suggests the wood may have potential for producing pulp, fiber, chip products, and particleboard. Veneer has been made out of alligator juniper on an experimental basis, but large trees are too few and scattered in most locations to make this venture economically feasible [6,103]. Volume estimates from upper woodland zones of Arizona range from 100 to 250 feet3/acre and average 150 feet3/acre. At lower elevations volume averages only 109 feet3/acre [10].
Alligator juniper can be made into particleboard and is occasionally milled as lumber. The wood is also used to make furniture. It is most commonly used to make various novelty products such as bookends, lamp bases, or small chests. Alligator juniper wood is fragrant with an attractive color and grain [10].
Alligator juniper makes excellent firewood of relatively high heat value [103]. The wood is light, easy to split, and burns with a pleasant aroma [115]. It provides an estimated 243,000 BTUs/foot3. Weight (lbs) per standard cord has been measured as follows [10]:
| oven-dry | air-dry | green |
| 2,264 | 2,536 | 3,736 |
IMPORTANCE TO LIVESTOCK AND WILDLIFE:
Alligator juniper is an important component of the southern portion of pinyon-juniper woodlands. This association provides good quality habitat for numerous species including mule deer, bighorn sheep, pronghorn, wild horse, coyote, bobcat, badger, porcupine, rabbits, mice, voles, woodrats, squirrels, and many species of birds [41]. Alligator juniper provides shade and shelter for wildlife and livestock. Pinyon-juniper woodlands provide valuable winter and, in some instances, year-round range for elk, deer, and livestock in parts of Arizona and New Mexico [112]. Both mule deer and white-tailed deer use alligator juniper stands in parts of southeastern Arizona [5]. At least 73 species of birds are known to breed in pinyon-juniper, and 32 species overwinter in these woodlands [56].
The berry-like cones of alligator juniper remain on the tree for a considerable length of time and, when abundant, provide a rich and readily available food source for many birds and mammals [6,41]. Cone-berries of junipers are often available at a time of year when other food sources are scarce [56]. Some researchers report that bird densities in pinyon-juniper woodlands may be up to 70% greater during bumper cone years than in average years [9]. Both birds and mammals are capable of consuming large quantities of juniper cone-berries and are extremely important dispersal agents [6]. Cone-berries provide food for coyotes during the summer, fall, and winter; they assume particular importance during the fall [105]. In some areas, both deer and elk eat juniper cone-berries during the winter months [119]. Alligator juniper is also an important food source for the collared peccary in parts of New Mexico [19].
Alligator juniper cone-berries are believed to be an important component in winter wild turkey diets in north-central Arizona [131]. "Cone-berries may be particularly important to wild turkeys during drought years [50]. In New Mexico, an endangered subspecies of wild turkey, the Gold's turkey, feeds on alligator juniper [102]. The prevalence of juniper cone-berries may determine the densities of overwintering birds such as the Townsend's solitaire, western and mountain bluebirds, and the American robin [50]. Some avian species consume both the pulpy flesh and seeds of juniper cone-berries (Cassin's finch, evening grosbeak); others, which are more important dispersal agents, digest only the pulp and disperse the seed (bluebirds, American robin, and Townsend's solitaire) [56].
The foliage of alligator juniper is apparently somewhat more palatable than the foliage of most other junipers [32] and, consequently, is more often utilized as browse. Research indicates that the mean volatile oil content of alligator juniper is less than that of either Rocky Mountain or Utah juniper. Foliage is also believed to have less of an inhibitory effect on bacterial rumen of deer [116]. Alligator juniper is reported to be an important year-round mule deer food in parts of New Mexico [88]; in southeastern New Mexico, it is considered a major food item from January through March [113]. In parts of south-central New Mexico, it is a common although not preferred item in mule deer diets [87]. In the Dos Cabezos Mountains of southeastern Arizona, alligator juniper is reported to be one of the seven most important foods of both mule deer and white-tailed deer. Although important to both species, it was eaten nearly twice as often by mule deer [5]. The foliage of alligator juniper frequently represents a major item in elk diets in Arizona ponderosa pine stands [28]. It has little forage value for most livestock but is sometimes eaten by domestic goats [32,75].
PALATABILITY:
The foliage of alligator juniper relatively unpalatable to livestock and most wild ungulates. Palatability of alligator juniper for mule deer has been reported as follows [76,100]:
winter - high to low
spring - moderate to low
summer - moderate to low
fall - high
NUTRITIONAL VALUE:
Little specific information exists on the food value of alligator juniper. The cone-berries apparently provide at least moderate energy for a number of bird species [9]. Researchers have estimated the average energy value of a juniper cone-berry at 315.31 calories [114].
COVER VALUE:
Alligator juniper provides shade and shelter for many wildlife species and for domestic livestock [29]. Woodrats are known to use alligator juniper as support structures for nests [126]. A New Mexico study found that the percentage of shelters that white-throated woodrats constructed from alligator juniper was as follows [126]:
live trees 4.3
dead trees 2.2
The broad-tailed hummingbird, acorn woodpecker, ash-throated flycatcher, Mexican jay, black-crested titmouse, bushtit, blue-gray gnatcatcher, and rufous-crowned sparrow breed in pinyon-juniper habitats dominated by alligator juniper in the Chisos Mountains of Texas [132]. Alligator junipers provide nest sites for many bird species, and older trees may contain hollow cavities at the bases that are used by cavity nesters [93]. Alligator junipers provide hiding and thermal cover and migration corridors for a variety of animals. Young trees provide cover for elk, deer, and small mammals. This cover may be particularly important when deep snows make other food sources unavailable [98]. Miller and Wigand [93] report that mule deer often move from shrub communities to juniper woodlands during winter stress periods.
VALUE FOR REHABILITATION OF DISTURBED SITES:
Alligator juniper aids in preventing erosion on harsh sites [30]. It can be successfully propagated by seed [7].
OTHER USES AND VALUES:
Wood of alligator juniper was formerly made into charcoal in parts of the Southwest [6]. During historic times the wood of many species of juniper was used as fenceposts, poles, mine timbers, fuel for the mining industry, and railroad ties [8,10,41].
Springfield [120] notes that juniper wood may have potential for use in making charcoal and for producing certain chemicals. Wood extractives of alligator juniper may be of value although the precise characteristics of the extractives of this species are poorly known. Extractives from morphologically similar species are used in making pharmaceuticals, perfumes, polishes, and insecticides [10].
Juniper wood is associated with traditional values in a number of Native American cultures. The wood has traditionally been used in construction of pueblos and hogans, and for making corrals and fences [94]. The cone-berries of alligator juniper were used in traditional foods, medicines, teas, and in ceremonial incense [30,94,95]. The Zuni used alligator juniper cone-berries to flavor foods such as cornbread and blood sausage. They used the shreddy bark to make torches [95].
OTHER MANAGEMENT CONSIDERATIONS:
Pinyon-juniper woodlands have been increasing in extent since settlement times. In many parts of the Southwest, alligator juniper and other species have encroached into adjacent grasslands [60,99,134]. A decrease in fire frequency has often been cited as the probable cause of this increase [133]. However, overgrazing offers another possible explanation. Past management efforts have largely focused on halting the juniper "invasion" through mechanical or chemical means. Little regard was given to possible wildlife use of these areas or to potential wood products value of juniper species. In a number of instances, juniper removal alone does little to increase long-term forage potential. Miller and Wigand [93] note that although juniper is largely accepted as providing beneficial wildlife habitat, there is significant disagreement as to how much juniper is optimal, the acceptable size of treated areas, the effect of thinning as opposed to total juniper removal, and whether particular sites should or should not be treated.
Several types of mechanical treatments have been used with varying success in converting pinyon-juniper woodlands to grasslands. Cabling, chaining, bulldozing, and other mechanical means of removal are most effective in eliminating mature, even-aged, nonsprouting junipers in stands of approximately 250 trees or less per acre. Elimination of alligator juniper is often difficult however, because of its proclivity to sprout following disturbance. Even repeated defoliation may be ineffective [65]. Brush choppers, hand-cutting, and rottocutters also appear to be relatively ineffective for killing alligator juniper [120]. According to Jameson and Johnsen [62], the root crown must be removed for good results to be obtained through mechanical control. Severson [117] reported little difference between treated and untreated plots in New Mexico 13 to 18 years after mechanical removal. No significant differences were detected between untreated and thinned plots or between pushed/left and pushed/piled/burned plots, although significant (p <0.05) differences were observed between bulldozed and untreated/thinned treatments. Density (stems/ha) of alligator juniper on four treatments in 1983 was as follows [117]:
| untreated | thinned | pushed/left | pushed/piled/burned |
85 |
38 |
5 |
3 |
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 <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].
Phanerophyte
REGENERATION PROCESSES:
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:
| trees with sprouts | |||
| stump diameter (in.) | # trees observed | # |
% |
1-6 |
156 |
140 |
90 |
7-12 |
27 |
18 |
67 |
13-30 |
37 |
22 |
59 |
31-48 |
2 |
0 |
0 |
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
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]:
| community description | postfire year |
| skeletal forest & bare soil | 0 |
| annuals | 2 |
| perennial grass/forb | 4 |
| shrub | 25 |
| shrub/open tree | 100 |
| climax pinyon-juniper | 300 |
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 ECOLOGY OR ADAPTATIONS:
Although exact fire histories are difficult to determine, evidence suggests that fire was common in pinyon-juniper communities before European-American settlement [21]. It is thought that in presettlement times, lower elevation woodlands of southeastern Arizona were relatively open with a fire-maintained dense grass understory [8]. The role of fire in Madrean ecosystems, in which alligator juniper occurs as an important component, is largely unknown [13,77]. It is suspected that fires usually occurred here during the annual dry period from May through late July [77]. Most research indicates that fire-free intervals have increased in pinyon-juniper communities, leading to downslope juniper invasion of grasslands and shrublands in parts of the Great Basin, Arizona, and Texas [37]. Reductions in fine fuels by grazing and active fire suppression are often cited as probable reasons for longer fire-free intervals [21,37,40].
Alligator juniper canopies are often high enough so that fires scorch but do not severely damage the crown [74]. The bark also provides protection from fire. Kittams [74] reports that alligator juniper bark is seldom burned by fires in Chihuahuan Desert communities.
Alligator juniper is generally capable of prolific sprouting after aboveground vegetation is consumed by fire, particularly if the "resprouting zone" is covered by soil. By sprouting, alligator juniper may survive fires of even high intensity [107,135] and quickly regains dominance on most sites [67,107,135,121]. Mortality of even small trees generally appears to be low [67]. Alligator junipers typically sprout from the root crown following fire [133]. Susceptibility to fire may also be greater during drought years [121].
The range of fire intervals reported for some species that dominate communities where alligator juniper occurs are listed below. To learn more about the fire regimes in those communities refer to the FEIS summary for that species, under "Fire Ecology or Adaptations."
Rocky Mountain ponderosa pine (Pinus ponderosa var. scopulorum): 2 to 40 years
Mexican pinyon (P. cembroides): 20 to 70 years
POSTFIRE REGENERATION STRATEGY:
Tree with adventitious bud/root crown/soboliferous species root sucker
Ground residual colonizer (on-site, initial community)
Secondary colonizer - off-site seed
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".
IMMEDIATE FIRE EFFECT ON PLANT:
Alligator juniper appears resistant to the effects of fire [12,74,133]. Consequently mortality of alligator juniper is generally low, even after fires of relatively high severity [107].
The probability of mortality may depend at least in part, on the size of the tree. In many instances the smallest alligator junipers appear to be most susceptible to fire-caused mortality [67]. As many as 32% of alligator junipers < 3 inches (7.6 cm) in dbh were killed after a hot June wildfire in southeastern Arizona [16]. Trees with a dbh of 31 inches (79 cm) or more do not resprout and may be killed by fire. Following a hot June fire in northern Sonora and southeastern Arizona, many of the large alligator junipers suffered severe damage and subsequently died [43]. However, large alligator junipers are not always killed by fire. Researchers have observed fire scars on old alligator junipers which indicate these large trees have survived many surface fires [34,97].
Kittams [74] reports that alligator juniper bark is seldom burned by fires in the Chihuahuan Desert. Irregular strips of the fibrous bark tend to remain attached to the alligator juniper for many years after the plants have been killed by fire [10].
DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
Alligator juniper mortality following an August wildfire in an oak-juniper woodlands of Arizona was estimated at 28% [67].
Temperatures lethal to alligator juniper tissue vary according to desiccation, and thus season of burn. Site characteristics also may contribute to the specific effects of fire. During a 2-year study, lethal temperatures ranged from 147 degrees Fahrenheit (63.8oC), which was recorded in summer, to 174 degrees Fahrenheit (80.0oC), which was observed during the late fall. Detailed data follow [59]:
These findings indicate greatest susceptibility to fire during dry, hot months. Annual variation is also probable.
PLANT RESPONSE TO FIRE:
Alligator juniper is capable of prolific sprouting after aboveground vegetation is consumed or damaged by fire [67,107]. Basal sprouts have been observed on trees as young as 1 year [62]. Sprouts generally grow rapidly with favorable weather conditions [133]. Alligator juniper can quickly regain dominance after fire on Arizona rangelands [107]. Approximately 42% of all living alligator junipers sprouted from the base after an August wildfire in oak-juniper woodlands of Arizona [16].
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
No entry
FIRE MANAGEMENT CONSIDERATIONS:
Prescribed fire is commonly used to reduce juniper dominance. Management objectives include controlling juniper and shrubs, increasing forb production, enhancing habitat diversity, increasing herbivore diversity, enhancing nutritive quality and palatability of forage, and preparing sites for reseeding. On some sites, substantial control of trees by fire may last for up to 50 years, with linear reductions in herbaceous cover as the overstory develops. Where pinyon-juniper cover exceeds 20%, increases in herbaceous plant growth after fire may be low, but where the canopy cover is less, perennial grasses may respond quickly. On sites with high tree cover, however, annuals may quickly invade and can prevent the establishment of a perennial herb community [21]. Alligator juniper may be eliminated in ponderosa pine forests in which underburns occur at 3 to 7 year intervals [71].
Prescribed fire may not be an effective management tool where pinyon-juniper is in an advanced successional state or on sites dominated by exotic annuals. If desirable perennials fail to establish, the site can be left open and susceptible to weed invasion or soil erosion. Fine fuel loading is critical when planning burns in pinyon-juniper woodlands. Sites with < 600 kg/ha fine fuels will be difficult to burn with the intensity needed to scorch and kill alligator juniper [21].
The following methods have been used in attempts to reduce alligator juniper on Arizona rangeland:
1) broadcast burning
2) burning individual trees
3) burning grasslands to kill junipers less than 3 ft (0.9 m) in height
4) burning scattered, wind-rowed, or piled pinyon-juniper slash after mechanical treatment
None of these methods has been entirely satisfactory. Broadcast burning in these communities requires a density of 200 to 400 trees per acre, air temperatures around 85 to 90 degrees Fahrenheit (29-35oC), relative humidity of 4 to 8%, and an average wind speed of 10 to 20 mph (16-32 km/h) [107]. Burning individual trees is both costly and labor intensive, and relatively ineffective for sprouters such as alligator juniper [61,107,120]. Blackburn and Bruner [15] have recorded 40% mortality following individual burning of alligator juniper.
When mechanical treatment is combined with fire, two-way chaining tends to windrow the slash, producing a better burn which kills more small trees [107].
To increase habitat diversity, several small burns (<20 ha) may be more effective than a single large burn. Disadvantages include increased cost and greater likelihood of damage by grazing. Bunting [21] reports an optimum burn size of approximately 500 to 2,500 acres (200-1000 ha) where hand-firing techniques are to be used, and larger areas where aerial ignition is planned. Where fuel loading is irregular, smaller areas within a larger burn unit can be ignited under conditions of lower temperature and higher fuel moisture, but this often leaves larger amounts of the unit unburned.
It is difficult to date fire scars of alligator juniper. It may stop growing when soil moisture is unavailable and resume growth when soil moisture conditions improve. This growth pattern produces "false rings," and makes counting rings extremely difficult [50,97].
Because strips of bark tend to remain on alligator juniper for many years after fire, early utilization of fire-killed trees may be somewhat limited. The use of chemical debarking agents may allow for better immediate utilization of the wood [10].
Palatability of alligator juniper foliage is enhanced by fire [74]. Young shoots may be particularly palatable to herbivores.
FIRE CASE STUDY CITATION:
Tirmenstein, D., compiler. 1999. Response of alligator juniper to
burning in an Arizona shrub oak ecosystem.
In: Juniperus deppeana. In: Fire Effects Information System, [Online].
U.S. Department of Agriculture, Forest Service,
Rocky Mountain Research Station, Fire Sciences Laboratory (Producer).
Available: https://www.fs.usda.gov
/database/feis/ [
].
REFERENCE:
Bock, Jane H.; Bock, Carl E. 1987. Fire effects following prescribed burning in two desert ecosystems.
Final Report: Cooperative Agreement No. 28-03-278. Fort Collins, CO: U.S. Department of Agriculture,
Forest Service, Rocky Mountain Forest and Range Experiment Station. 20 p. [17].
SEASON/SEVERITY CLASSIFICATION:
Spring burn. Conducted on May 25th, 1984. Severity was not specified. Four of five plots recorded fireline intensities of 8 to 58 kW/m. Fireline intensity at the first plot was 260 kW/m.
STUDY LOCATION:
Lyle Canyon in southeastern Arizona. The canyon is located in the foothills on the west side of the Huachuaca Mountains.
PREFIRE VEGETATIVE COMMUNITY:
The preburn community was a scrub oak woodland. Dominant grasses included sideoats grama (Bouteloua curtipendula), plains lovegrass (Eragrostis intermedia), Texas beardgrass (Andropogon cirratus), and Hall's panicgrass (Panicum hallii). Common herbs were goldeneye (Viguiera annua), spreading snakeweed (Dyschoriste decumbens), and Louisiana sagewort (Artemisia ludoviciana). Wait-a-minute bush (Mimosa biuncifera), velvet-pod (Mimosa dysocarpa), and yerba de pasmo (Baccharis pteronioides) were common shrubs. Emory oak (Quercus emoryi) and Arizona white oak (Q. arizonica) were dominant tree species. A few alligator junipers (Juniperus deppeana) were present.
TARGET SPECIES PHENOLOGICAL STATE:
Not reported. Burn was conducted "prior to the growing season."
SITE DESCRIPTION:
Elevation - approximately 4,921 feet (1,500 m)
Mean January minimum temperature - 29 degrees Fahrenheit (-1.75oC)
Mean June maximum temperature - 90 degrees Fahrenheit (32.4oC)
Average annual precipitation - 17 inches (430 mm); 1/2 to 2/3rds between July and September
FIRE DESCRIPTION:
The fire occurred on May 25th from 10 AM to noon under hot, dry, calm conditions:
Air temperature - 90 to 92 degrees Fahrenheit (32-33oC)
Relative humidity - 16 to 18%
Winds - variable; gusts of 5 to 10 mph (8-16 km/hour)
Dead fuel moisture - 5 to 6% (fine fuels)
FIRE EFFECTS ON TARGET SPECIES:
Number of alligator juniper trees per 60 m2 subplot on experimental vs. control plots (N = 50 subplots per treatment year) was:
| Burn | Control | |||||||
| year | mean | std. dev. | year | mean | std. dev. | t | P | |
| prefire (1983) | 0.08 | 0.34 | 1983 | 0.08 | 0.27 | 0 | NS* | |
| postfire (1984) | 0.06 | 2.24 | 1984 | 0.10 | 0.36 | 0.65 | NS | |
| postfire (1985) | 0.18 | 0.90 | 1095 | 0.08 | 0.27 | 0.75 | NS | |
| *NS=not significant |
| year | Burn | Control |
| 1983-1984 | +0.06 | +0.02 |
| 1984-1985 | +0.04 | -0.02 |
FIRE MANAGEMENT IMPLICATIONS:
Bare ground was significantly greater on burned plots in postfire years
1 and 2 (P = t(P) of 0.88 (NS), 6.79 (<0.001, and 2.58 (<0.02) respectively).
There was little impact on woody plant densities, including alligator juniper.
This study was part of an extensive of body of research on fire effects in semidesert grassland, oak savanna, and Madrean oak woodlands of southeastern Arizona. See the Research Project Summary of this work for more information on burning conditions, fires, and fire effects on more than 100 species of plants, birds, small mammals, and grasshoppers.
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