Growth rate following fire: On burned sites in New Mexico and
Texas, Pinchot's junipers regained approximately 50% of their mature height 3 to 7 years after fire [6].
Reduction in canopy cover: Prescribed fire in northeastern King
County, Texas, caused a decrease in canopy cover of Pinchot's juniper 4 and 8 years following burning. Burned
sites were chained 4 to 8 years prior to burning. Both fires took place in March under a prescription of air
temperatures at 70 to 78 ðF (21-26 ðC), 25% to 40% relative humidity, and wind speeds ranging from 12 to 24
km/hr. From the time of burning until plant cover was measured in 1986 (4 and 8 years postburning), the burned
sites were continually grazed at a rate of 1 cow-calf/20 to 22 ha and received light quail hunting pressure.
There were no significant (P<0.05) differences between treatments, but cover of Pinchot's juniper was
greatest on unburned sites (~13.5%), followed by 8-year-old burns (~7%), and 4-year-old burns (~5%) [57,58].
Pinchot's juniper cover declined 3, 6, and 7 years following fires in Eddy County, New Mexico, and Culberson
County, Texas. Fires were ignited either by lightning or human negligence. Specific cover data for Pinchot
juniper are not presented, but total woody shrub cover (Pinchot's juniper, lechuguilla (Agave lechuguilla),
smooth-leaf sotol (Dasylirion leiophyllum), beargrass (Nolina spp.), prairie wattle
(Acacia angustissima var. texensis), catclaw mimosa, and resinbush (Viguiera stenoloba))
on 3-year-old burn sites was 6.5% versus 10.3% on comparable unburned sites. On 6- to 7-year-old burn sites,
woody shrub cover was 6.7% compared to 8.7% on unburned sites. The researchers note that lechuguilla,
smooth-leaf sotol, and sacahuista lost in excess of 50% of their total cover on burned sites [6].
This description provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keys for identification are available (e.g., [22,28,38,52,60,120]).
Pinchot's juniper is a native, drought-tolerant, evergreen large shrub or small tree, from 3 to 25 feet (1-8 m) tall [22,28,38,60,100,113,120,130]. On gypsum soils in Texas, Pinchot's juniper forms 3-foot-tall thickets covering several hundred acres [100]. Multiple stems arise from the base of Pinchot's juniper, forming a dense clump [22,28,38,39,60,100,113,120]. The leaves are triangular-ovate, 1.5 to 2.5 mm long, 0.5 to 1.2 mm wide, and pressed together in groups of 2 or 3 [38,113]. Pinchot's juniper forms seed cones, commonly referred to as "berries". Cones are 4 to 10 mm long [28,113] and bear 1 or 2 seeds [22,28,60,113,120]. From initiation of growth, cones require 1 year to reach maturation [22,28,60,120]. Pinchot's juniper has a "vigorous" [95], shallow [9], lateral root system [65]. The bud zone of Pinchot's juniper develops from stem meristematic tissue located in the axil of the cotyledons on newly germinated seedlings [102,103]. Pinchot's juniper plants on shallow, rocky soil generally have an exposed bud zone until they are 10 to 15 years of age. On deep soils, the bud zone is generally covered by soil prior to 10 years of age [86]. Plants as old as 170 years have been identified on isolated buttes in Garza County, Texas [25,78].
Toxicity: Pinchot's juniper plants contain toxic monoterpenes. Juvenile Pinchot's juniper plants are lower in total monoterpenes than mature Pinchot's juniper plants [108]. The toxic monoterpenes act as a defense mechanism against browsing, thereby promoting survival and reproduction of Pinchot's juniper [90]. Foliage monoterpene composition data are available [1].
Fire adaptations: Pinchot's juniper establishes after fire by seed [8,71,85,98,113,125] and by sprouting from basal buds [6,22,54,68,69,70,73,83,98,100,108,113,120]. Approximately 30% of young plants with exposed basal bud zones sprout following fire, compared to 97% of older plants with soil-protected basal buds [73].
FIRE REGIMES: In its presettlement habitat on steep, rocky sites lacking fine fuels, Pinchot's juniper was largely protected from fire [73,77,129]. However, overgrazing, fire suppression, and recurrent drought have facilitated the encroachment of Pinchot's juniper into the Rolling and High Plains of Texas [10,23,26,61,71,73,81,90,101,114]. A fire-return interval of 20 to 30 years is needed to prevent encroachment of Pinchot's juniper and maintain natural grassland conditions [71,103]. Where Pinchot juniper occurs in pinyon-juniper woodlands, productive sites can sustain patchy fires at intervals of 10 to 50 years. Densities sufficient to sustain crown fires would occur at intervals of 200 to 300 years. In open stands with continuous grasslands, fire-return intervals may be 10 years or less [35].
The following table provides fire return intervals for plant communities and ecosystems where Pinchot juniper is important. 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".
Community or Ecosystem Dominant Species Fire Return Interval Range (years) plains grasslands Bouteloua spp. <35 blue grama-buffalo grass Bouteloua gracilis-Buchloe dactyloides <35 [82,134] juniper-oak savanna Juniperus ashei-Quercus virginiana <35 Ashe juniper Juniperus ashei <35 [82] creosotebush Larrea tridentata <35 to <100 [48,82] pinyon-juniper Pinus-Juniperus spp. <35 [82] Colorado pinyon Pinus edulis 10-400+ [29,36,53,82] galleta-threeawn shrubsteppe Pleuraphis jamesii-Aristida purpurea <35 to <100 [82] mesquite Prosopis glandulosa <35 to <100 [63,82] mesquite-buffalo grass Prosopis glandulosa-Buchloe dactyloides <35 Texas savanna Prosopis glandulosa var. glandulosa <10 oak-juniper woodland (Southwest) Quercus-Juniperus spp. <35 to <200 [82] oak savanna Quercus macrocarpa/Andropogon gerardii-Schizachyrium scoparium 2-14 [82,121] shinnery Quercus mohriana <35 [82] live oak Quercus virginiana 10 to<100 Fayette prairie Schizachyrium scoparium-Buchloe dactyloides <10 [121] little bluestem-grama prairie Schizachyrium scoparium-Bouteloua spp. <35 [82] *fire return interval varies widely; trends in variation are noted in the species reviewPrescribed fire to control Pinchot's juniper: Prescribed fire to control the encroachment of juniper into grasslands is most effective when juniper size and densities are low and grassland communities support enough fine fuel to carry fire [9]. Pinchot's juniper is difficult to kill with fire unless the basal bud zones are above the soil. If the bud zone is exposed, prescribed fire can result in 70% to 75% mortality [86,106]. To maximize Pinchot's juniper mortality with fire, the foliage must be ignited and a crown fire generated [73]. Varied burning intervals are recommended depending upon site characteristics. On deep soils, the basal bud zone of Pinchot's juniper may become buried earlier, necessitating a prescribed burning regime of 7 to 10 years. In contrast, on shallow soils, the bud zone may take longer to bury, allowing for a prescribed burning regime of 15 to 20 years [106].
While Pinchot's juniper is difficult to kill with fire when the basal buds are buried, fire reduces Pinchot juniper's impact on associated herbaceous species. When Pinchot's juniper establishes on a site and reaches dominant status, few herbaceous plants grow under the plant (See Forage Production). Because Pinchot's juniper canopy cover decreases after fire, prescribed fire can promote an increase in desirable grasses and forbs on sites encroached by Pinchot's juniper [105,115,133]. Additionally, areas burned to remove Pinchot's juniper are usually not invaded by other woody species following fire [86]. It should be noted that burning during a dry year increases Pinchot's juniper mortality, but forage productivity can be reduced by as much as 50% after prescribed burning in a dry year [106].
To prevent soil loss, prescribed burning of Pinchot's juniper should be used on flat to gently sloping sites (0% to 12% grade), and use of fire should be limited on steeper slopes [105]. Prescribed fire should be conducted in late winter or early spring, prior to green-up, with relative humidity of 25% to 40%, air temperatures of 70 ðF to 80 ðF (20-30 ðC), and wind speeds of 8 to 15 mph [106]. The optimal season for burning live Pinchot's juniper foliage is most closely correlated to foliage moisture content (r=0.73) and average mean daily temperature (r=0.48). During drought conditions, the most relevant factors are foliage moisture content (r=0.83) and relative humidity (r=0.77). During above normal precipitation, no significant (P<0.01) correlation occurs, making fire behavior unpredictable [16,17]. Guidelines for developing a fire prescription management plan in Pinchot's juniper communities are available in the literature [86,106,110,140].
Chaining/dozing and fire: Chained and dead Pinchot's juniper is a highly volatile fuel [86,120]. Pinchot's juniper is commonly controlled by chaining followed by burning 3 to 5 years later [9,64,131,132]. Waiting for a period of 3 to 5 years after chaining permits fuels to dry and allows Pinchot's juniper seeds to germinate so that seedlings will also be killed by the fire [105,106].
In northwest Texas grasslands, stands of Pinchot's juniper were chained at ground level and 2 feet (0.6 m) above ground in March 1997. Prior to chaining, Pinchot's juniper cover was 30%, and following chaining (both treatments) cover was less than 1%. Four years after chaining, the plots were burned in February and early March 2001. Air temperature, relative humidity, and wind speed just prior to the fires averaged 65.3 ðF (18.5 ðC), 40.1%, and 17.58 km/hr. Herbaceous fine fuel averaged 990 kg/ha (range 800-1,100 kg/ha) and the fire intensity, based on flame length, was "low" to "moderate". Six years after chaining and 2 years after fire, Pinchot's juniper cover was 4% on sites chained to ground level and 6% on elevated chained sites. On untreated sites, cover of Pinchot's juniper increased from 30% to 51% from 1996 to 2003 [9].
Wright and others [138] have developed an "expert system" for burning large pastures of dozed Pinchot's juniper, with inputs of windspeed, time of day, air temperature, topography, green juniper moisture content, fuel type, and nearness of cold front.
Fire economics: Literature is available on prescribed fire cost associated with Pinchot's juniper removal [74,76,87]. In general, aerial ignition of Pinchot juniper stands with a heliotorch is the most economical burning method available to managers [135,137,138,139].
Effects on wildlife: In northeastern King County, Texas, northern bobwhite quail prefer unburned Pinchot's juniper sites. Density estimates (mean number of birds/100 ha(SE)) of bobwhite quail on unburned sites was 60.5(11.8) and 55.1(9.2) on 8-year-old burns, and 43.3(7.6) on 4-year-old burns (For fire details, see Discussion and Qualification of Plant Response to Fire) [57,58].
Following fire, deer (species not identified) preferentially browse Pinchot's juniper crown sprouts in the Chihuahuan Desert. Crown sprouts grow up to 12 inches (30 cm) during postfire year 1 and up to 2 feet (60 cm) by the end of postfire year 3. Deer also browse new foliage on old branches that survive fire [54].
Grazing: After early spring prescribed fires, managers should wait until at least mid-June before stocking range sites with livestock. A 10- to 20-year burning cycle can maintain productive range sites, reducing the need for chemical and/or mechanical controls of Pinchot's juniper [86,105].
Monoterpene levels following fire: Following a prescribed burn, total monoterpene concentrations were measured in 3- and 11-month-old sprouts, and in unburned mature Pinchot juniper plants. In the 3- and 11-month-old sprouts, monoterpenoid concentrations were 5.1 and 10.0 g/mg, respectively, and 12.2 g/mg in the unburned, mature Pinchot's juniper plants. Monoterpene levels were significantly (P<0.05) less in the 3-month old sprouts, suggesting that young Pinchot's juniper plants invest resources in photosynthesis rather than defense [108].
Pinchot's juniper occurs in open flats, dry hillsides, canyons, arroyos, caprock regions, and talus slopes [28,38,43,60,83,94,100,113,120]. Prior to European settlement, Pinchot's juniper occurred only on shallow, rocky sites with northwest exposures [7,21,77,92,98,105] (See Successional Status). Where Pinchot's juniper encroaches on grasslands, it generally occurs on rough, broken terrain between plains, and on range sites with shallow soils along the High Plains and Rolling Plains of western Texas [105].
Climate: Pinchot's juniper occurs in a subtropical climate zone with dry winters and long, hot summers [58,73,112,141].
At 2 sites (High Plains and Rolling Plains) in western Texas, Pinchot's juniper establishment from 1950 to 1979 was highly correlated (r not given) with precipitation during cool spring and fall periods preceding establishment. Though Pinchot's juniper seed production was not quantified, observations made by McPherson and Wright [71] indicated that substantially greater seed production occurred in 1986, when total precipitation from January to September equaled 20 inches (600 mm), than during 1984 or 1985, when total precipitation from January to September equaled 6.7 and 15 inches (170 and 390 mm), respectively. Successive years of above-average cool-season precipitation at the 2 sites prompted a significant (P<0.05) increase in Pinchot's juniper establishment. Establishment was near double during these periods versus periods of normal or below normal precipitation on the High Plains (Mean(SE)=5.7%(0.9) vs. 2.1%(0.5)) and Rolling Plains (Mean(SE)=5.0%(0.6) vs. 2.6%(0.7)) [71].
Elevation: Pinchot's juniper primarily occurs at elevations of 1,000 to 3,300 feet (300-1,000 m) [28,94,141]. It may, however, grow at elevations as high as 5,000 feet (1,500 m) in New Mexico [60].
Soil: Pinchot's juniper primarily occurs on limestone or gypsiferous soils [22,28,38,81,83,100,127].
Pinchot's juniper foliage moisture is related to available soil moisture, as influenced by soil texture. In the Texas Rolling Plains, Pinchot's juniper foliage moisture content was recorded from September through November 1995.
Approximate percent moisture content in Pinchot juniper foliage and soils on 3 sites in the Texas Rolling Plains at 4 sample dates [75]Site
clay flat sandy bottomland shallow clay Sample date soil foliage soil foliage soil foliage 26 September 19 53 13 56 10 53 12 October 13 51 9 55 6 52 26 October 10 47 5 50 5 47 9 November 10 48 5 51 4 48Soil and foliage moisture contents were highest in September and lowest in November. Foliage moisture was highest on sandy soils on all sampling dates, although the clay flat soil tended to have the highest total moisture content [75].
Mature Pinchot's juniper with a soil-protected basal bud zone is generally only top-killed by fire [6,54,72,100,113]. Age, canopy development, slope, and soil surface stability are determining factors in the rate at which Pinchot's juniper's bud zone is covered by soil and therefore protected from fire [103]. Low- to moderate-severity fire can kill Pinchot's juniper seedlings and saplings if the basal bud zone is not protected by soil [102,103,106,113]. Mature plants with the basal bud zone elevated above the soil surface can experience mortality rates up to about 70% following fire, while about 3% mortality occurs in plants with a soil-protected basal bud zone [73,86]. Pinchot's juniper seeds can survive and germinate following fires [125].
Considerable heat is required for Pinchot's juniper ignition to occur, but once ignited, the plants burn so vigorously that all branches are killed [6,54]. Pinchot's juniper "readily" ignites when foliage moisture content falls below 70% [73,77].
Pinchot's juniper is a low value browse species for livestock and wildlife [26]. Livestock seldom browse Pinchot juniper except during winter when herbaceous species are dormant and other browse has lost its leaves [84]. In Carlsbad Caverns National Park, New Mexico, mule deer browse substantially more Pinchot's juniper in years of poor growth of more desirable forage species [55]. The berries of Pinchot's juniper are a valuable food source for numerous species of birds and small mammals [59,128]. Insects on the Rolling Plains of Texas are also known to feed on Pinchot's juniper [81].
Domestic goats will browse Pinchot's juniper, especially during the dormant season, but intake is limited because of postingestive feedback from the monoterpenes in Pinchot's juniper [13,24,108]. Pinchot's juniper consumption affects rumen metabolism. Domestic goats (Angora and Spanish) that consume Pinchot's juniper as 30% of their diet for 10 days exhibit an increase in total volatile fatty acid production along with changes in proportional volatile fatty acid concentrations. In domestic goats, intraruminal dosing for 9 days with Pinchot juniper oil (0.18g oil/kg bodyweight) results in cachexia and mild hepatic injury at low doses in the form of lipid vacuolization. At higher doses (0.36g oil/kg bodyweight) cellular necrosis and lobular encapsulation occur after 9 days [108]. Domestic goats dosed with activated charcoal may consume more Pinchot's juniper for a short period of time (up to 6 days), since activated charcoal attenuates the negative feedback associated with Pinchot's juniper [13].
Domestic Spanish goats consume significantly (P<0.01) more Pinchot's juniper than do domestic Angora goats in Texas in all seasons [24]. Female Spanish goats browse significantly (P<0.05) more Pinchot's juniper during spring and summer than do Angora goats [84].
Palatability/nutritional value: Pinchot's juniper contains monoterpenes which negatively affect palatability [24,84,108]. In particular, terpinene, terpineol, and terpinen-4-ol are most responsible for the unpalatability of Pinchot's juniper to most wildlife and livestock [44].
Pinchot's juniper is described as "moderately" nutritious [108]. The plant has a dry matter digestion range of 57% to 66% and a crude protein range of 6% to 9%. Domestic goat consumption of Pinchot juniper throughout the year, particularly during the dormant season, may increase the likelihood that domestic goats meet their nutritional requirements. Pinchot's juniper consumption, at a maximum of 30% of their diet, may also result in a favorable shift of volatile fatty acid production towards lower acetate:propionate ratios, thus improving feeding efficiency. Also, low levels of Pinchot's juniper (at or below 30% of their diet) may induce both stage I and stage II detoxification enzymes [108].
Nutritional/mineral content (%) of Pinchot's juniper fruit and foliage for one measurement date each in Sutton County, Texas [30]
Plant partHuston and others [49] measured the composition of Pinchot's juniper leaves 11 times from 1973 to 1976 on Edwards Plateau, Texas.
Compositional range of Pinchot's juniper leaves during 11 measurement dates [49]
Collection date Composition (%) Water Ash Cell wall Phosphorus Protein Digestible organic matter 4/73 - 7/76 46-56 4-6 34-37 0.08-0.17 6-9 57-66Cover value: Pinchot's juniper provides valuable cover for numerous wildlife species [26,116]. It has a high cover, escape, and thermal value for white-tailed deer on the Edwards Plateau and the Rolling Plains of Texas [15]. Many species of birds us Pinchot's juniper for nesting and roosting cover [119,120,128].
Pinchot's juniper is listed as a dominant species in the following locations and vegetation
classifications:
New Mexico:
Colorado pinyon (Pinus edulis)-Pinchot's juniper/shrub live oak
(Quercus turbinella)/sideoats grama (Bouteloua curtipendula) in the Gila National Forest [45]
Pinchot's juniper/creosotebush (Larrea tridentata) in the Guadalupe Mountains
from 3,500 to 4,500 feet (1,100-1,400 m) [109]
Pinchot's juniper/sideoats grama-hairy grama (B. hirsuta) in
the southwestern part of the state [46]
Pinchot's juniper/blue grama (B. gracilis) woodlands of the
Great Plains [93]
Texas:
Pinchot's juniper/blue grama woodlands of the
Great Plains [93]
Mohr oak (Q. mohriana)-Pinchot's juniper/sideoats grama shrublands
of Texas [93]
Pinchot's juniper-midgrass (species not defined in classification) series in the
Rolling Plains and High Plains [20]
Ashe juniper-Pinchot's juniper in central and south-central Texas, especially the
Edwards Plateau [98]
Regions:
Pinchot's juniper/sideoat grama-hairy grama association in the Chihuahua Desert
[89]
The Comanche Native Americans used Pinchot's juniper as a treatment for headaches, vertigo, and other ailments. The leaves were dried over hot coals and inhaled. They also used an extract of the dried and pulverized roots to alleviate menstrual problems [113]. Pinchot's juniper was also used in the construction of bows and arrow shafts by the Kiowa, Comanche, Cheyenne, and Apache Native Americans [38].
Wood Products: The wood of Pinchot's juniper is used locally for fence posts [83,120] and fuel [47,120], but is of little commercial importance.
Pinchot's juniper staminate and pistillate cones open during September and October [38,111]. In pinyon-juniper woodlands, Pinchot's juniper cones open for pollination in late fall, and seeds mature in the late spring [34].
Phenological development of Pinchot's juniper recorded at biweekly intervals during 1968 and 1969 in Garza County, Texas [96] Phenological stage Date of occurrence Bark begins to slip March 15 to April 1 Staminate and pistillate cones open April 1 to 15 and October 1 to 15 Start of leader elongation April 15 to May 1 Bark begins to stick September 15 to October 15 Leader elongation stops October 15 to November 15 Dormant period November 15 to March 15Total volatile oil concentrations in Pinchot's juniper twigs were measured seasonally at the Texas A&M Agricultural Research Station in 1991. Volatile oil levels were greatest during summer (14.34 õg/g) and spring (10.65 õg/g), followed by winter (7.42 õg/g) and fall (6.90 õg/g) [90]. Extensive data on variations of 34 volatile oils in Pinchot's juniper between summer and winter in New Mexico and Texas is available [2].
Pinchot's juniper regenerates via seeds [8,71,85,98,113] and sprouting from basal buds [22,68,69,70,73,83,85,98,100,112,113].
Pollination: As of this writing (2007) information on pollination of Pinchot's juniper is not available in the literature; however, it is likely wind-pollinated.
Breeding system: Pinchot's juniper is typically dioecious [28,38,60,68,120], though most populations have a small percentage of monoecious individuals [68,116]. In Snyder and Borden counties, Texas, 3.9% of 258 mature Pinchot's juniper trees evaluated were found to be morphologically monoecious [68].
Seed production: Pinchot's juniper reproductive maturity at 2 sites (xeric upland and mesic lowland) in western Texas was more strongly correlated (r=0.59) with tree height than with age, stem diameter, crown volume, or basal area. Eighty-six percent of trees taller than 3.41 feet (1.04 m) on upland sites produced berries, compared to 78% on lowland sites. Computer models suggest that Pinchot's juniper plants reach maturity at 25 years of age on upland sites and 16 years on lowland sites. However, age was a less accurate predictor of sexual maturity than tree height. A negative correlation between Pinchot's juniper maturity and herbaceous cover was weak but significant (P=0.05). This suggests that increases in herbaceous cover may slow Pinchot's juniper growth and maturity [68].
Mature Pinchot's juniper trees produce berries nearly every year. Cones initiate growth in October and/or November and mature a year later [68]. "Large" seed crops are produced in the autumn following wet spring and summer seasons [126]. In the Rolling Plains and Edwards Plateau region of Texas, Warren and Britton [126] estimate that average Pinchot's juniper seed production for 1997 and 1998 was 6,517 and 511 seeds/plant, respectively. Seventy-one percent of the seeds produced in 1997, and 82% of the 1998 seeds were not viable. The viable seeds produced in the autumn of each year did not start germinating until June, and germinated at a rate of 33% and 26% for 1997 and 1998, respectively. For seeds produced in autumn 1997, approximately 770 seeds/plant were still contained within dried berries on the plant in autumn 1998 [126].
Seed dispersal: Pinchot's juniper seeds are dispersed by wildlife, livestock, wind, and surface water [8,19,34,37]. Ansley and others [8] state that Pinchot's juniper seeds in grassland areas devoid of mesquite (Prosopis ssp.) are dispersed by small mammals, wind, and surface water. Where mesquite is present, birds likely disperse Pinchot's juniper seeds by resting and/or perching on mesquite branches and defecating previously consumed Pinchot's juniper seeds, or stopping to eat Pinchot's juniper fruits on mesquite branches. Pinchot's juniper seedlings are common beneath mesquite canopies in northwest Texas. In fact, Pinchot's juniper seedlings often mature and eventually overtop mesquite nurse plants. Fence posts and powerlines also serve as perch sites for birds and likely account for the establishment of Pinchot's juniper seedlings along fence lines in abandoned and reseeded fields. In Sonora, Texas, Pinchot's juniper seeds were found in the feces of raccoon, fox, and ringtail [19].
Pinchot's juniper seed passage through animal digestive tracts reduces germination. Seeds collected in western Texas directly from the plant and from coyote scat and bird droppings were planted in greenhouse. At the end of 120 days, 11% of the seeds from plants had germinated while only 3% of seeds collected from animal feces had germinated [124].
Seed banking: Pinchot's juniper forms a seed bank [79,126]; however information is lacking on seed longevity. In the Rolling Plains and Edwards Plateau regions of Texas, Warren and Britton [126] estimate the subsurface Pinchot's juniper seed bank size to average 68,298 seeds/plant. However, 90% of the seeds retrieved by researchers were empty and the germination rate of filled seeds was less than 1% over 1 year.
Germination: Pinchot's juniper seeds germinate and emerge optimally when soils are moist and the temperature is 64 ðF (18 ðC). This suggests that germination occurs during warm, wet periods in spring and fall [8,102,113]. Smith and others [102] found that no Pinchot's juniper seeds germinated at a soil temperature of 50 ðF (10 ðC) and limited germination occurred at 81 ðF (27 ðC). Seed germination may require a 120-day period of "cold" stratification [11].
Fire effects on germination: Pinchot's juniper seeds can survive and germinate after fire [125]. Prior to burning, 3 groups of Pinchot's juniper seeds were placed in the path of prescribed rangeland fires in Lubbock and Lamb counties, Texas, during February and March. Two groups of seeds were removed from their berries and either barely covered with soil or placed on the soil surface between and within clumps of vegetation (species not given). A third group was left in the berries and placed on the soil surface between and within clumps of vegetation. Seeds were exposed to fire for between 80 to 250 seconds. Four hours after fire exposure, the seeds were collected and placed in pots with sandy clay loam soil. At the time of the publication, seeds from all 3 groups had germinated and produced seedlings (no specific data given). Seeds covered by soil produced the most seedlings, followed by seeds left in the berries on the soil surface [125].
Seedling establishment/growth: According to PLANTS Database [113], Pinchot's juniper requires 2 years of above-average precipitation for seedling establishment. However, McPherson and Wright [71] found that from 1950 to 1979 on the High Plains and Rolling Plains of Texas, most seedlings established during the 1st year of a wet (above average precipitation) 2-year period (43.0% and 44.4%, respectively). Above average precipitation for a 2-year period occurred 10 times from 1950 to 1979. The researchers note that this study took place on sites that were either continuously lightly grazed (Rolling Plains) or continuously heavily grazed (High Plains) and thus the results should not be extrapolated to ungrazed sites.
Depth of buried seed is important for Pinchot's juniper seedling establishment. In a seeding trial conducted by Smith and others [102], no Pinchot's juniper seedlings emerged from planting depths greater than 0.8 inch (2 cm) [102].
Blue grama has a significant (P<0.05) negative effect on the growth of Pinchot's juniper seedlings. In a controlled study, Pinchot's juniper seeds (100/box) were planted in boxes with 2 densities of blue grama seedlings, 2 months following blue grama seed germination. Pinchot's juniper growth was significantly higher in control boxes without blue grama seedlings than in boxes with blue grama competition. No significant difference occurred between the 2 levels of blue grama grass competition [102].
Degree of competition Pinchot's juniper attributes Shoot length (cm) Root length (cm) # of stem branches # of root branches Dry weight (g/plant) Control 31.8 97.3 28.7 51.3 4.72 16 blue grama plants 6.8 28.7 0.4 7.4 0.07 32 blue grama plants 6.7 23.1 0.0 4.0 0.05In north-central Texas, Pinchot's juniper seedling growth is stunted in the presence of sideoats grama, buffalo grass (Buchloe dactyloides), and tobosa (Pleuraphis mutica), but increased growth occurs under intact canopies of honey mesquite (Prosopis glandulosa) [111]. When all grasses were removed from the site, Pinchot's juniper seedling basal diameter and height significantly (P<0.01) increased. Pinchot's juniper seedlings grew significantly (P<0.01) less in the presence of buffalo grass than with tobosa and/or sideoats grama. Conditions within buffalo grass communities are more stressful (lower infiltration rates and less soil surface shading) than in the taller sideoats grama and tobosa communities, which contributes to slower growth of Pinchot's juniper [111].
Nurse plants: On the high plains of western Texas, Pinchot's juniper establishment and persistence are facilitated by honey mesquite [18,72]. Pinchot's juniper seedlings favor honey mesquite canopies due to increased nutrient availability and shading, which ameliorates extreme summer temperatures. Pinchot's juniper seedlings in grasslands grew significantly (P<0.05) less in height and diameter than those under honey mesquite canopies. At sites where honey mesquite was removed, Pinchot's juniper seedlings basal diameter increased significantly (P<0.05) less than when growing under honey mesquite canopies [111]. On relatively xeric sites of the High Plains of Texas, the density of small Pinchot's juniper plants (<3 feet (1 m)) is significantly (P<0.05) higher under the canopies of honey mesquite than in areas devoid of the plant. In the same area, Pinchot's juniper acts as a nurse plant for agarito (Mahonia trifoliolata), littleleaf sumac (Rhus microphylla), and catclaw mimosa (Mimosa aculeaticarpa var. biuncifera) [72].
Vegetative regeneration: Pinchot's juniper "rapidly" sprouts from basal buds following disturbances such as fire or top removal [22,69,70,83,100,113,120]. Sprouting after top removal is influenced by tree size, season of top removal, and soil type, as demonstrated by the studies summarized below.
In Garza County, Texas, Pinchot's juniper plants in 5 size classes were cut to ground level in January to December. Eighty-three percent of cut plants produced some growth 1 year after cutting. Pinchot's juniper basal circumference and growth were positively correlated (r=0.996), with the smallest plants producing the least growth. When analyzing month of top removal, plants cut in December produced significantly (P<0.05) more biomass 1 year later than plants cut in any other month. Plants cut in December produced approximately 2.2 pounds (1 kg) of biomass, with the second most growth occurring in plants cut in March (~0.8 pounds (375 g)). Pinchot's juniper cut from April through September had significantly (P<0.01) less growth than plants cut during other time periods [96].
On the Texas Rolling Plains, Tunnell and Mitchell [112] cut 50 Pinchot's juniper trees to approximately a 4-inch stump height in July 1996. By October 1997, over 90% of cut trees had sprouted. The researchers note that as tree size increases, so does the probability that it will sprout following top removal.
Pinchot's juniper plants were cut to ground level on deep clay and clay loam soils in the Texas Rolling Plains and on shallow clay loam soils on the Texas High Plains. Following top removal, Pinchot's juniper survival of plants less than 20 years old was significantly (P<0.01) less on shallow soils (Mean(SE)=67.1%(4.5)) than on deep soils (Mean(SE)=80.8%(2.6)). There were no significant differences in survival rate for plants older than 20 years, since at that age the basal bud zone of Pinchot's juniper is sufficiently buried to ensure survival. At both sites, survival of Pinchot's juniper was significantly (P<0.05) reduced by the presence of other Pinchot's juniper plants and soapweed yucca (Yucca glauca) [69].
Warren and Britton [123] found that Pinchot's juniper sprouts are capable of growing roots when removed from the parent plant. The researchers cut 100 six-month-old sprouts, planted them in soil, and subjected them to a light/temperature regime of 12 hours of light at 74 ðF (23 ðC) and 12 hours dark at 50 ðF (10 ðC) for 120 days. At the end of the experiment 3% of the sprouts had formed tiny roots.
Pinchot's juniper has some shade tolerance, as it can establish under the canopies of shrub live oak (Q. turbinella) and honey mesquite [72,105]. Pinchot's juniper's place in the successional gradient is not discussed in the literature. However, it occurs in both early seral conditions such as burn sites [6,22,54,83,100,108,120] and late seral conditions such as isolated relict buttes in Garza County, Texas [25,78].
Species displacement: Increasing cover of Pinchot juniper on the Edwards Plateau of Texas is having a debilitating effect on herbaceous species. Dye and others [23] studied the interaction between Pinchot's juniper and understory species from the stem base outward to 18 feet (6 m) beyond the canopy of Pinchot's juniper. Primary herbaceous species occurring in proximity to Pinchot juniper included grasses such as Wright's threeawn (Aristida purpurea var. wrightii), red grama (Bouteloua trifida), hairy woollygrass (Erioneuron pilosum), curlymesquite (Hilaria belangeri), fall witchgrass (Digitaria cognata), Texas wintergrass (Nassella leucotricha), Texas grama (B. rigidiseta), buffalo grass, and Reverchon bristlegrass (Setaria reverchonii); and forbs such as needleleaf bluet (Houstonia acerosa var. acerosa), Parks' stoneseed (Lithospermum parksii), woody crinklemat (Tiquilia canescens), grassland croton (Croton dioicus), leatherweed (C. pottsii), and longstock greenthread (Thelesperma longipes). The basal cover, density, biomass, and species richness of the primary herbaceous species decreased significantly (P≤0.05) from 18 feet (6 m) beyond Pinchot's juniper canopy inward to the stem base. The negative effect of Pinchot's juniper was more pronounced on shallow soils (Kimbrough association), than on deep soils (Angelo and Tulia associations). Two years following selective poisoning of Pinchot's juniper plants with picloram, total herbaceous biomass on Kimbrough, Angelo, and Tulia soils increased from 1,300, 1,780, and 1,290 kg/ha, respectively, to 2,140, 2,140, and 1,560 kg/ha, respectively [23]. In western Texas, McPherson and others [65] found similar interactions between herbaceous species and Pinchot's juniper. On both grazed and ungrazed sites, herbaceous cover was significantly (P<0.01) lower under Pinchot's juniper canopy compared to interspaces. However, Pinchot's juniper had little influence on herbaceous cover 10 to 16 feet (3-5 m) from the edge of the tree canopy.
Fire: Postfire succession models in juniper-dominated (Juniperus spp.) ecosystems in the Intermountain West show a progression from annuals to perennial grasses to grass/shrub mix to juniper dominance over time. Given that junipers studied in the Intermountain West do not sprout after fire, the return of Pinchot's juniper to dominance after fire probably occurs more quickly than other juniper species, perhaps within 20 years [9].
Juniperus pinchotii, commonly known as Pinchot juniper or redberry juniper, is a species of juniper native to south-western North America, in Mexico: Nuevo León and Coahuila, and in the United States: south-eastern New Mexico, central Texas, and western Oklahoma.
It grows at altitudes between 600 and 2,100 metres (2,000 and 6,900 feet).[2][3]
Juniperus pinchotii is an evergreen coniferous shrub or small tree growing to 1–6 metres (3+1⁄2–19+1⁄2 feet) tall, usually multistemmed, and with a dense, rounded crown. The bark is pale gray, exfoliating in thin longitudinal strips, exposing orange brown underneath. The ultimate shoots are 1.1–1.8 millimetres thick. The leaves are scale-like, 1–2 mm long and 0.5–1.5 mm broad on small shoots, up to 12 mm long on vigorous shoots; they are arranged in alternating whorls of three or opposite pairs. The juvenile leaves, produced on young seedlings only, are needle-like.
The cones are berry-like, with soft resinous flesh, subglobose to ovoid, 5–8 mm (rarely 10 mm) long, orange-red, often with a pale pink waxy bloom, and contain one or two seeds; they are mature in about 12 months from pollination. The male cones are 3–4 mm long, and shed their pollen in fall. It is usually dioecious, with male and female cones on separate plants, but occasional monoecious plants can be found.[2][3]
Hybrids with Juniperus coahuilensis are known.[3] They have also occasionally been reported with Juniperus monosperma, but never verified; all claimed hybrids tested have proven not to be. These two are unable to hybridize in nature, being isolated by pollination time (autumn for J. pinchotii, late winter for J. monosperma).[3]
Juniperus pinchotii, commonly known as Pinchot juniper or redberry juniper, is a species of juniper native to south-western North America, in Mexico: Nuevo León and Coahuila, and in the United States: south-eastern New Mexico, central Texas, and western Oklahoma.
It grows at altitudes between 600 and 2,100 metres (2,000 and 6,900 feet).
