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Abies bracteata

Table of Contents SUMMARY INTRODUCTORY DISTRIBUTION AND OCCURRENCE BOTANICAL AND ECOLOGICAL CHARACTERISTICS FIRE EFFECTS AND MANAGEMENT MANAGEMENT CONSIDERATIONS APPENDIX REFERENCES
	Figure 1—Bristlecone fir on Cone Peak, Monterey County, California. Image by Mark W. Skinner, hosted by the USDA-NRCS PLANTS Database. Used with permission.

SUMMARY

INTRODUCTORY

Literature cited in this Species Review include these reviews: [16,46]. A dissertation by Talley (1974) provides original documentation of bristlecone fir ecology, and it is cited throughout this Species Review [59].

Common names are used throughout this Species Review. See table A1 for a complete list of plant species mentioned in this review.

DISTRIBUTION AND OCCURRENCE

Figure 2—Bristlecone fir distribution. Map courtesy of the U.S. Department of the Interior, Natural Resources Conservation Service. [2020, May 22] [61].

Bristlecone fir is endemic to California (fig. 2). Its geographic range is extremely narrow; it occurs only in the northern Santa Lucia Mountains of central-coastal California, in Monterey County [7,22,41,47,60] and extreme northwestern San Luis Obispo County [26,41,51,56]. It is distributed 1.5 to 14 miles (2.5-22 km) from the coast, with most groves (wooded areas with little or no underbrush) situated 2.5 to 9 miles (4-15 km) inland [59]. It grows mostly on public land: it occurs across a narrow strip (55 × 13 miles (88 × 21 m)) in the Ventura Wilderness of the Los Padres National Forest and in U.S. Army's Fort Hunter [16,55]. It is the rarest fir in North America [16,26]. As of 2013, there were ~1,000 bristlecone fir trees on the Los Padres National Forest [46].

Bristlecone fir has been successfully planted in Mediterranean regions of Europe, but plantings in the northeastern United States have not been successful [16].

States: CA [61]

SITE CHARACTERISTICS AND PLANT COMMUNITIES
Terrain and plant communities in the Santa Lucia Mountains are complex and diverse. Rapid climate shifts along an elevational gradient, and complex geology and topography, result in plant community differences across short distances. The elevational difference of nearly 1 mile (1.6 km) within a 3-mile (5-km) distance; a variety of slope exposures and soil types; the influence of the cool marine layer at low elevations; the very steep gradient of precipitation; and a variety of slope exposures and soils create a very steep gradient of environments and plant communities from low to high elevations [11].

Site Characteristics: Bristlecone fir requires a mild climate with minimal winter frost and relatively low summer evaporation rates [2,54]. Climate in the Santa Lucia Mountains is mediterranean with a maritime influence [16,44,59]. Temperatures within bristlecone fir's narrow range are moderate, rarely below 0 or above 100 ^oF (-17 or 38 ^oC), although exposed ridges have wider fluctuations in temperature [44,47]. Annual precipitation averages 20 to 50 inches (500-1,300 mm) [16,59]. Rainfall is sparse from June through September (averages <2% of total) [59], and snowfall is uncommon [44,47].

Bristlecone fir grows at lower elevations than most firs [22]. Its overall range extends from 690 to 5,250 feet (210-1,600 m) [3,16,59,60]. In surveys across its range, more than half of bristlecone fir's distribution was above 3,280 feet (1,000 m) [40,59], with the highest elevational distribution on Cone Peak [16].

Bristlecone fir occurs on a variety of slope positions. It grows in relatively cool, moist canyons [9,16,29,39,47,51,55,56]; on terraces and ridges [9,55,56]; and on barren, steep, rocky sites [9,16,25,51,55,60]. Bristlecone fir is most common northerly or east-facing slopes [9,16,47,56,59], but it also grows on south- and southeast-facing slopes above 4,500 feet (1,400 m) [16,59]. On southerly sites and at low elevations, it almost always grows on relatively moist, sheltered sites [16]. Forest slopes supporting bristlecone fir groves average 25^o; the steepest slopes are up to 44^o. Large, open groves occur on steep slopes, although the largest groves occur on relatively level ridges and plateaus with deep, coarse soils [59]. Terrain of groves in sandstone soils is relatively flat [59]

Soils supporting bristlecone fir are highly variable, with a wide variety of substrates and soil textures [49]. They are largely derived from metamorphic (mostly granitic) parent materials in the northern portion of the Santa Lucia Mountains, but parent materials also include schist, gneiss, and marble [55,59]. Igneous and marine sediment parent materials, including basalt and sandstone, dominate the substrate of the southern portion of bristlecone fir's range [59]. It can grow in serpentine and other ultramafic parent materials [49]. Bristlecone fir usually grows in coarse soils, although it also grows in fine-textured soils (i.e., clay and loam) [56,59]. Soils are usually thin and poorly developed, although the largest individuals tend to grow in mixed-evergreen forests with deeper soils [28]. Pinchot (1908) reported that "where it makes its best growth the soil is usually porous and fairly deep, but near its upper altitudinal limit the tree often grows in shallow beds of coarse rock fragments" [47]. Soil pH ranges from very strongly acidic to mildly alkaline [52] (~4.5-7.8 pH).

Plant Communities: Bristlecone fir occurs in coastal temperate, mixed-evergreen and mixed-conifer woodlands and forests [22,28] and riparian woodlands [8]. Within these plant communities, it may grow in mixed stands or grow in distinct groves (small wooded or forested areas, usually with no undergrowth). Bristlecone fir is most likely to form pure stands at high elevations [47].

Bristlecone fir is most common in the canyon live oak [25,42,59] phase of mixed-evergreen sclerophyll forests [3,25,59,60]. At low elevations in mixed-evergreen forests, it also grows with coast live oak, Pacific madrone, tanoak, redwood, and/or Shreve oak [16,46,55,56], just above the redwood forest zone [26,59]. It fingers into the fog belt of redwood forests [6,16,26] and into chaparral [9,31]. At mid- to high elevations in mixed-evergreen forests, it grows with incense-cedar and interior live oak [2,27,55,56]. Associates in mixed-conifer forests include coast Douglas-fir, ponderosa pine, and sugar pine [2,9,16]. Commonly, pines are associates at highest elevations [39]. Coulter pine is an associate in the southern portion of bristlecone fir's distribution [4,16].

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

Bristlecone fir is a medium-sized conifer [47]. It is typically 30 to 100 feet (10-30 m) tall at maturity [16,59], but some individuals reach 160 feet (50 m) tall [59]. Diameter at breast height is from 4 to 12 inches (10-30 cm); rarely, up to 40 inches (100 cm) [16,47]. The tallest individuals grow in deep ravines and on ocean-facing slopes. Stunted individuals grow on exposed, cold ridges and at high elevations [47]. For summit, transition, and ravine sites, mean heights of 100-year-old bristlecone firs were 40, 70, and 90 feet (12, 21, and 27 m), respectively [59]. The champion tree is 127 feet (39 m) tall, 150 inches (380 cm) in circumference, and 36 feet (11 m) in spread [1]. The bole of bristlecone fir is straight and limby, tapering rapidly [39,47], and the crown is narrow and spikey [2,16,47] (fig. 1). Branches may extend to the ground [3,16,22,39,60], and they become droopy with age. Bark is smooth and thin [2,16]; bark thickness measurements were lacking in the literature. Needles are 1.0 to 2.4 inches (2.5-6.0 cm) long [16,22,60]. Needles are unusually sharp [2,36], wide, and long [59] for a fir, and they have a strong, pungent odor [22,31]. Seed cones are <3.5 inches (9 cm) long [60]; usually, 1.6 to 2 inches (4-5 cm) long, and only occur in the top of the crown [36,59]. They are resinous [36,39] and covered with thin spines (bract scales, see fig. 3); hence, the common name "bristlecone fir". These spines are unique among Abies species [22]. Bristlecone fir is the only fir in which the bract scales extend far out from the cone scales [40]. Seeds are about 0.2 inch (5 mm) long. Seed wings are about as long as the seed [22].

Figure 3—Bristlecone fir seed cone. Image by Charles Webber, California Academy of Sciences. Used with permission.

Most bristlecone fir groves are small and scattered [10,14,36,47,59]; generally, they are <5 acres (2 ha) [10,14,47]. In 1908, Pinchot reported that no bristlecone fir groves contained more than 200 trees [47]. The canopy layer in bristlecone fir groves is usually continuous, the shrub layer open to intermittent, and the herbaceous layer sparse [9]. Groves are typically uneven-aged except at highest elevations, where even-aged structure predominates, probably due to rare wet years that favored synchronous establishment [59].

Bristlecone firs may live longer than 200 years [38].

Pollination and Breeding System: Bristlecone fir is wind pollinated [38].

Successful reproduction requires outcrossing. Unsuccessful selfing is apparently high in bristlecone fir. For six populations across bristlecone fir's range, levels of inbreeding were high in seed embryos but not in mature trees, suggesting high rates of embryo and seedling death [38]. Genetic diversity of bristlecone fir is low compared to other California conifers [37,38], with low rates of within- and between-population genetic differentiation [38].

Seed Production: Pinchot (1908) reported bristlecone fir was a "moderately vigorous" seed producer [47]. Large cone crops are reported [25], with 3 to 5 years between large crops [17,47]. Large cone crops are usually followed by years of little to no cone production [59]. Larvae of fly [17,33,39], moth [33], and chalcid wasp [17,33,59] species reduce seed yields. Predispersal seed predation may near 100% in some years. Seed predator populations usually peak the year after a large cone crop [59]. Following that population peak, however, seed production and seed predator insect populations may remain out of phase for at least 3 years. Therefore, Talley (1974) [59] concluded that "claims that cone parasites are endangering the fir are not valid".

Production of viable seeds appears low, probably due to inbreeding. The study of six populations found production of filled seeds varied widely, ranging from an average of 18.6 seeds/cone in the Villa Creek population to 93.7 seeds/cone in the Cone Peak population (the largest population sampled). Total number of seeds/cone (filled and unfilled) ranged from 188.0 seeds/cone in the Cone Peak population to 255.4 seeds/cone in the Miller Canyon population [38].

Age at first seed production was not reported. Trees >100 years old continue to produce seeds [9]. Based on age class distributions, Talley (1974) estimated that for high-elevation groves, only one or two bristlecone firs/century reach cone-bearing age [59].

Seed Dispersal: Wind, gravity, and animals disperse the seeds [9].

Seed Banking: Bristlecone fir has a soil seed bank [17], although the length of time the seeds remain viable was not reported in the literature.

Even though cones ignite easily, seeds within unburned cones may survive surface fire [25].

Germination: Pinchot (1908) reported that germination rates appear low [47]. Observations suggest that highest germination rates occur in mineral soil [16,47]. Fresh seeds are germinable [17,59], but overwinter stratification improves germination rates [9,59]. In a field study, germination of planted seeds was low in exposed, steep, and/or high-elevation sites. Few or no seedlings emerged in annual grassland, chaparral, and summit mixed-conifer communities. Germination was highest (10%) at midelevations [59].

Seedling Establishment and Plant Growth: Pinchot (1908) wrote that seedling establishment "is fairly good throughout the range of the species" [47]; however, dry soils and drought limit bristlecone fir establishment. Open to lightly shaded, moist sites with mineral soil apparently favor bristlecone fir establishment. Talley (1973) noted that the greatest bristlecone fir establishment occurred in open redwood—mixed-evergreen forest ecotones, and seedlings in closed, mixed-evergreen forests did not survive to the sapling stage [59].

Limited evidence suggests that seedling mortality is high [38,59]. Bristlecone fir seedlings are drought-sensitive [40,59], and water stress greatly limits bristlecone fir establishment and growth. Field and laboratory experiments showed bristlecone fir establishment was positively correlated with light shade, warm winter and spring temperatures, low summer temperatures, northerly slopes, and fine-grained soils. Ravine and ravine-midelevation transition sites supported more bristlecone firs of all age classes than terraces and high-elevation sites (P < 0.05 for all variables). These variables were most likely to coincide in mixed-evergreen forests in the canyon live oak phase [59]. Talley (1974) found most seeds planted on annual grassland, chaparral, and summit forest sites failed to establish, which he attributed to desiccation of germinants. However, bristlecone fir established from seeds planted on low-elevation coastal canyon sites and on a site that had burned the previous year. Seedlings at highest elevations required shade to establish [59].

Bristlecone fir grows fastest on fine-grained soils (i.e., those with high water-holding capacity). However, because bristlecone firs on these soils are more susceptible to fire than those on coarse-grained soils (see Fire Adaptations and Plant Response to Fire), groves on fine-grained soils are rare [59]. Talley (1974) concluded that fire and deep shade limit growth to the sapling stage at low elevations, while drought limits bristlecone fir seedling establishment at high elevations [59].

Vegetative Regeneration: Firs do not naturally reproduce vegetatively [17].

FIRE EFFECTS AND MANAGEMENT

The widely scattered pattern of bristlecone fir groves is attributed to fire mortality across the landscape [16]. Severe fire may remove entire bristlecone fir groves from a site [25]. In the 1977 Marble Cone Fire on the Los Padres National Forest, most bristlecone firs survived because they were growing on steep, rocky slopes with light fuel loads that did not burn. Nearly all bristlecone firs on the edges of canyon live oak communities were killed, but the largest tree (52 inches (132 cm) diameter) survived "with no damage" [25].

The resinous seed cones ignite easily, likely killing the seeds within [39]. Seeds within unburned cones may survive surface fire [25].

These postfire regeneration strategies are likely, although they are not well documented:
Crown residual colonizer (on site, initial community)
Initial off-site colonizer (off site, initial community)
Secondary colonizer (on- or off-site seed sources)

Fire Adaptations and Plant Response to Fire: Bristlecone fir establishes from wind- and animal-dispersed seeds after fire [59]. Surveys of postfire seedling establishment of bristlecone fir had not been conducted as of 2020. However, Griffin (1978) postulated that bristlecone fir may establish from viable crown-stored seeds after surface fire, even if fire killed the parent trees [25]. Talley (1974) observed that seed production and seedling establishment following the 1970 Buckeye Fire was "excellent" [59].

Bristlecone fir is primarily a fire avoider, often growing on rocky sites with thin, poorly developed soils and sparse fuels [9,14,26,28,44,56,59]. Based on field surveys and Forest Service, U.S. Department of Agriculture fire records, Talley (1974) found that basal area of bristlecone fir was positively associated with sites showing little or no evidence of fire; with steep, fuel-limited, rocky sites; and with fine-grained soils (P < 0.05). He found that 54% of the variance in bristlecone fir basal area was correlated with fire severity (P < 0.0001) [59]. Fire effects to and response of bristlecone firs growing in relatively moist canyon bottoms was not addressed in the literature as of 2020.

Fire effects to and postfire recruitment of bristlecone fir were largely anecdotal as of 2020. In the 1970 Buckeye Canyon Fire, Talley (1974) noted that although surrounding mixed-evergreen forest experienced crown fire, the Spruce Fork grove experienced only surface fire, and mature bristlecone firs showed only "minor, local damage". The steepest slopes showed no evidence of fire, and bristlecone fir saplings on those slopes were undamaged [59]. Although the 1985 Rat Creek-Gorda Fire burned most of the Cone Peak Gradient Research Natural Area [32], most mature bristlecone fir in the area survived. Following the 2008 Basin Complex Fires, surveys in postfire years 5 and 6 found dead bristlecone firs in burned areas, with the highest mortality in the Ventana Double Cone grove. Surveyors noted some postfire bristlecone fir recruitment in two groves (California Natural Diversity Database 2017 data cited in [46]). In the 2016 Soberanes Fire, most bristlecone firs within the fire perimeter survived [46].

Griffin (1978) noted that many bristlecone firs escaped the 1977 Marble Cone Fire. The fire was mostly stand-replacing due to a large accumulation of dead brush and other fuels. However, most bristlecone fir groves were on steep, rocky terrain that did not carry the fire; only trees on the edges of the groves were killed. The largest bristlecone fir in the area (51 inches (129.5 cm) in diameter) appeared undamaged 10 months after the fire [25].

Anecdotal evidence suggests that postfire insect infestations kill more bristlecone firs than fires [46,59]. Griffin (1978) noted insect mortality of bristlecone firs that survived the Marble Cone Fire, and he suspected that insect damage would eventually kill more bristlecone firs than the fire. He based this supposition on the work of Talley (1974), who observed that two bristlecone fir groves lost only a small number of trees as a direct effect of the 1970 Buckeye Fire, but they had higher mortality rates as a result of "postfire insect damage [59]". Griffin (1978) speculated that although "some additional trees will die, ... the species and even individual groves are in no way doomed" [25].

Surface fuels in bristlecone fir groves are mainly dry grass and tree litter. However, because bristlecone fir has a narrow form and low branches, it can become a ladder fuel [59].

Sudden Oak Death was first noted in the Santa Lucia Mountains in the 1990s. It is caused by an oomycete (Phytophthora ramorum). As it spreads, it has had myriad ecological effects to the mixed-evergreen forests, including changes in stand structure and increasing standing dead and woody debris fuels. It infects coast live oak, Shreve oak, and tanoak [43,46].

Lightning fires occur throughout the Monterey Bay region from May to October [9,24]. Fuels are driest from June to July and from September to October, making ignition most probable during these periods [24]. Although historical fire sizes in the area are not well documented, most lightning fires in the Santa Lucia Mountains were apparently small [9,59], and they typically did not consume entire bristlecone fir groves [9]. However, some fires probably grew large; for example, a 1916 wildfire burned 7,000 acres (2,800 ha) in the Santa Lucia Mountains [24,25]). Fires may be of low [59], mixed, or high severity in bristlecone fir groves [9]. Fire intensity in bristlecone fir groves had not been quantified as of 2020.

It is unclear how American Indian-set fires affected presettlement fire regimes in the Santa Lucia Mountains [44]. When Spanish entered the area, the Monterey Bay region supported one of the densest aboriginal populations in North America. The American Indian population may have reached 26,000 in the area. However, there is no evidence that American Indians actively set fires in the Santa Lucia Mountains; the area mostly inaccessible because it is so steep and rugged [12].

Historical fire intervals were not documented for bristlecone fir groves as of 2020, but intervals are estimated at several decades to >100 years. Fire scars analyses are difficult to impossible because bristlecone fir groves usually escape fire or succumb to fire, so there is little information on historical fire frequencies in the groves [44]. Age class analyses of bristlecone fir, which could provide information on time-since-fire, had not been conducted as of 2020. In a review of 35 studies, fire intervals are estimated at 117 (mean), 93 (median), 90 (mean minimum), and 250 (mean maximum) years for fire-sensitive fir communities, including bristlecone fir. However, 80% of these studies were conducted in areas outside of California, and none were specific to bristlecone fir groves [63]. In the Santa Lucia Mountains, fire intervals ranged from 19 to 78 years, based on fire scars on sugar pines (time interval: 1640-1977). However, fire intervals for bristlecone fir groves on steep slopes with sparse fuels are probably longer than that. For mixed-evergreen forests of the Monterey Bay region, fire intervals are estimated at 30 to 135 years in historical times and a mean of 250 years in the 1990s [58]. For redwood forests, mean fire intervals are estimated at 135 years in historical times and 130 years in the 1990s [24]. These estimates are based on fire scar data, fire records, and modeling [24,58]. The California Native Plant Society (2020) estimated fire intervals of 50 to 100 years for bristlecone fir groves [9], but the basis for their estimate was not stated. LANDFIRE (2009) modeled fire intervals in mixed-evergreen forests of this region as mostly surface fires (81% of all fires), with a mean fire interval of 9 years and ranging from 5 to 30 years [35].

While estimates of contemporary fire intervals in bristlecone fir groves are lacking, fire records document several fires in the Santa Lucia Mountains from the 1930s onward. From 1931 to 1977, 39 lightning fires occurred in the Monterey County portion of the Santa Lucia Mountains [58,59]. From the 1970s to the 2010s, a series of mostly lightning-ignited fires burned in the Santa Lucia Range: the 1970 Buckeye Canyon (human-caused), 1977 Marble Cone, 1985 Rat Creek-Gorda, 1996 Wild Cattle, 1999 Kirk Complex, 2008 Basin Complex, and 2016 Soberanes fires (CalFire 2016 data cited in [46]). The fire interval for this period averages 7.7 years.

Find further fire regime information for the plant communities in which this species may occur by entering "bristlecone fir" on the FEIS home page.

MANAGEMENT CONSIDERATIONS

• FEDERAL LEGAL STATUS
• OTHER STATUS
• IMPORTANCE TO WILDLIFE AND LIVESTOCK
• VALUE FOR RESTORATION OF DISTURBED SITES
• OTHER USES
• OTHER MANAGEMENT CONSIDERATIONS

Palatability and Nutritional Value: Western grey squirrels eat bristlecone fir seeds, as do fly, moth, and chalcid wasp seed predators [33,59]. The sharply-pointed foliage is not palatable to mule deer [52] and likely, not to other potential browsers. Lanner (1999) reports that the "blade-thin and dagger-tipped" needles "easily pierce the skin of an impetuous foliage grasper" [36].

Cover Value: Birds and small mammals use bristlecone fir for cover [1].

VALUE FOR RESTORATION OF DISTURBED SITES
Bristlecone fir provides watershed protection [1,47] by reducing soil erosion and slowing water runoff. It is commercially available, although hard to obtain in some years [7]. Bristlecone fir seeds are stored in a laboratory seed bank for species conservation [5].

If outplanting is deemed necessary, Ledig et al. (2006) recommend collecting seeds from as many populations as possible, but concentrating seed collection in the two largest and most genetically diverse populations [38]:

Bristlecone fir is sometimes planted as an ornamental in areas with mild climates [59].

APPENDIX

REFERENCES:

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