Pinus jeffreyi



INTRODUCTORY


  Gerald and Buff Corsi © California Academy of Sciences
AUTHORSHIP AND CITATION:
Gucker, Corey L. 2007. Pinus jeffreyi. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].

FEIS ABBREVIATION:
PINJEF

NRCS PLANT CODE [183]:
PIJE

COMMON NAMES:
Jeffrey pine

TAXONOMY:
The scientific name of Jeffrey pine is Pinus jeffreyi Grev. & Balf. (Pinaceae) [32,54,68].

Jeffrey pine hybridizes with ponderosa pine (P. ponderosa) and Coulter pine (P. coulteri) where distributions overlap [43,48,112,214].

SYNONYMS:
Pinus ponderosa subsp. jeffreyi (Grev. & Balf.) E. Murr. [53]

LIFE FORM:
Tree

FEDERAL LEGAL STATUS:
No special status

OTHER STATUS:
Information on state-level protected status of plants in the United States is available at Plants Database.


DISTRIBUTION AND OCCURRENCE

SPECIES: Pinus jeffreyi
GENERAL DISTRIBUTION:
Jeffrey pine occupies sites throughout much of California and in southwestern Oregon, western Nevada, and northern Baja California [24]. In Nevada, Jeffrey pine is restricted to Washoe and Mineral counties. In Oregon, Jeffrey pine occurs in Curry, Josephine, Jackson, and Douglas counties [5]. The Laguna Mountains of San Diego County are the southern limit of Jeffrey pine in the United States [130], but Jeffrey pine is common further south in the Sierra Juárez and the Sierra San Pedro of Baja California Norte [211]. The US Geological Survey provides a distributional map of Jeffrey pine.

HABITAT TYPES AND PLANT COMMUNITIES:
On very dry sites and on serpentine soils, Jeffrey pine is often a climax species [2,129]. However on more productive sites and in mixed-conifer forests, Jeffrey pine's dominance is dependent on recurrent fire. Without fire or other disturbances that create gaps in the canopy, Jeffrey pine is often replaced by more shade-tolerant conifers such as white fir (Abies concolor) [42,106]. The following lists are vegetation classifications in which Jeffrey pine is dominant.

General, western United States:

Oregon: California: Nevada: Baja California Norte:

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Pinus jeffreyi

GENERAL BOTANICAL CHARACTERISTICS:
This description provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keys for identification are available (e.g., [54,69]).

Aboveground description: Jeffrey pine is a large, slow-growing, long-lived conifer [63,133]. Trees often live 400 or 500 years. In Jeffrey pine/huckleberry oak vegetation in central Sierra Nevada, the oldest Jeffrey pine tree was an estimated 631 years old [133]. Jeffrey pine may reach 200 feet (60 m) tall [69,112], and diameters of up to 8.2 feet (2.5 m) are reported [32]. Crowns are rounded [54] or long and symmetrical [111].

Tree maturity and site conditions affect form and size. Rounded crowns are typical for mature trees, and young trees often have pyramidal crowns. Lower branches are large and somewhat droopy, and upper branches are smaller and ascending [130]. At high-elevation sites, Jeffrey pine can be deformed by high winds [81].

The Jeffrey pine trunk is normally straight with thick, large plates of bark separated by deep furrows [32,54,130,198]. Jeffrey pine saplings and adults averaging 2 inches (5 cm) and 48.8 inches (124 cm) in diameter had estimated bark thicknesses of 0.2 inch (0.5 cm) and 2.6 inches (6.5 cm), respectively [62]. Fifty Jeffrey pine trees from the south slope of Mt Pinos in southern California with an average DBH of 21 inches (53 cm) had an average bark thickness of 2.1 inches (5.3 cm) [198].

Charles Webber © California Academy of Sciences

Needles are 3 to 11 inches (8-28 cm) long and most often in bundles of 3, but bundles of 2 are possible [69,112]. Needles are retained for 2 to 10 years [32,69]. Needle thickness varies with location on the tree and elevation. Needles in the sun are thicker than those in the shade, and needles on trees at high-elevation sites are thicker than those on trees at low-elevation sites [48]. Pollen cones are small, 0.8 to 1.4 inches (20-35 mm) long, and female cones are large, 4.7 to 12 inches (12-30 cm) long [69,112]. Cone size can vary between years and sites. The largest Jeffrey pine cones are produced in the Reno-Tahoe area, according to Haller [48]. Female cones mature 2 summers after being pollinated [64]. Jeffrey pine produces winged seeds. Seeds are between 10 and 13 mm long, and wings are up to 1.2 inches (3 cm) long [112,130]. Seed weight averages 123 mg (Forest Service, US Department of Agriculture, cited in [83]).

Belowground description: The Jeffrey pine taproot penetrates deeply, and lateral roots are considered "strong" and "extensive". In an open stand, on shallow ultramafic soils in the northern Sierra Nevada, Jeffrey pine roots up to 2 inches (5 cm) in diameter were found in a soil pit 100 feet (30 m) from the nearest tree [64].

Hybrids: Jeffrey pine hybrids are not especially common. They are described in Haller [48] and Zobel [214].

RAUNKIAER [136] LIFE FORM:
Phanerophyte

REGENERATION PROCESSES:
Jeffrey pine reproduces sexually through seed production and germination. Trees do not sprout after the loss of aboveground stems.

Pollination: Cones are wind pollinated.

Breeding system: Jeffrey pines are monoecious. A study of endemic and near-endemic California conifers revealed that Jeffrey pine was the most genetically diverse [91]. Outcrossing rates were high in 3 Klamath Mountain and 2 Sierra Nevada populations. Density of Jeffrey pine did not affect outcrossing rates, and evidence of severe inbreeding depression was lacking [38]. Jeffrey pine populations from serpentine soils in the Klamath Mountains and ultramafic soils in the southern Sierra Nevada were genetically similar, suggesting that directional selection likely has occurred on these sites. Klamath Mountain populations had lower heterozygosity levels than those in the southern Sierra Nevada, suggesting stronger directional selection or a past population bottleneck in the Klamath Mountain populations [37].

Seed production: Jeffrey pine has a "strong masting habit". Numerous seeds are shed within a few weeks every several years. Large cone crops occur at 2- to 4-year intervals [77,84]. Trees as young as 8 years old have produced cones, according to Krugman [77], but Rundel [142] reports that Jeffrey pine cones are not common until trees are at least 20 years old. In open Jeffrey pine/antelope bitterbrush forests in western Nevada's Whittell Forest and Wildlife Management Area, cone crop production ranged from 175 to less than 25 cones/tree over a 3-year period [195]. From cones produced on the eastern slopes of the Sierra Nevada in Mono and Madera counties, the number of fertile seeds/cone before seed dispersal averaged 222 and ranged from 160 to 338. From fallen cones collected at the end of April, the number of seeds/cone averaged 11 and ranged from 0 to 55. Of the available seeds, 14.8% were sound, 15.9% were aborted, and 69.2% had insect damage [180].

On eastern Sierra Nevada slopes in Lassen County, seed size and number were positively related to cone size, and seed size varied with position on the cone. Cones came from young, "thriftily growing" trees. Seed number and seed weight were greatest for large- and least for small-sized cones. For large cones, the largest number of developed seeds were concentrated in the middle cone region. For small cones, the largest number of developed seeds occurred in the upper cone region [110].

Seed survival is largely augmented by seed caching and seed feeding by small mammals and birds. The following studies conducted in western Nevada showed that, while seed removal rates may vary by seed availability and environment, removal is nearly complete regardless. In the Whittell Forest and Wildlife Management Area, the removal rate of radioactively-labeled Jeffrey pine seed from an open Jeffrey pine/antelope bitterbrush stand was 8.1 times faster in a mast than in a nonmast year (P<0.0001), but in any year, 98% to 99% of seeds were harvested. Of the removed seeds, a little more than 63% were found in rodent caches. The rest were either consumed or cached outside the study area. Yellow-pine chipmunk caches were most common, but a small percentage of caches were likely made by golden-mantled ground squirrels [195]. Seed removal rates did not consistently vary by elevation. Over a 2-year period, removal rates ranged from a low of 10.3%/day to a high of 71.7%/day at low-elevation sites. At midelevation sites, rates were not different between years, and at high-elevation sites rates ranged from 16.5% to 58.2%/day [47]. Along a transect through antelope bitterbrush shrublands with scattered Jeffrey pine into closed-canopy Jeffrey pine forests with thick litter, removal of Jeffrey pine seed was significantly faster in shrublands than in Jeffrey pine forests (P<0.005). Seed obscured by litter were removed at significantly slower rates than seed on the soil surface (P<0.001). Regardless of seed location, the researcher predicted that most (≥99%) seed would be removed before snowfall [191]. The movement and fate of seed cached in western Nevada is discussed below in the Seed dispersal, Seed banking, Germination, and Seedling establishment sections.

Seed dispersal: Jeffrey pine seeds are often moved through a combination of methods including gravity, wind, and small animals. A single seed may be dispersed through all 3 methods and relocated up to 6 times by animals. Observed and calculated dispersal distances through gravity and wind alone range from 3.48 feet (1.06 m) [67] to 89 feet (27 m) [85]. Dispersal distances reported from seed caching studies range from 8.5 feet (2.6 m) [192] to 206 feet (62.9 m) [190].

Gravity and wind: Of the North American conifers that produce winged seeds, Jeffrey pine seeds are typically heaviest. Without strong winds, the majority of seeds fall within 90 feet (27 m) of the parent tree [85]. However, observations in the field suggest much shorter dispersal distances [196]. If winds are gusty, Jenkinson [64] suggests that Jeffrey pine seed may be dispersed a distance 15 times the height of seed fall. Based on ballistics calculations, Jeffrey pine seeds falling from a height of 30 feet (10 m) in winds of 5 m/s would be deposited 55.4 feet (16.9 m) from the source [67].

In the Whittell Forest and Wildlife Management Area, wind rarely moved seeds already on the ground more than 8 inches (20 cm) from their original positions. The study was conducted in Jeffrey pine/antelope bitterbrush vegetation on nearly flat to slightly inclined terrain with sandy soils with small rocks and patches of plant litter. The maximum dispersal distance was 150 inches (380 cm) from the initial position. Most movement occurred within the first 8 of 37 monitoring days. Under natural conditions, wings often detach after a seed is wet or moved; permanent wings in this study may have increased the dispersal distance beyond what would have occurred under natural conditions [196].

Animal: Yellow-pine chipmunks rapidly dispersed and cached Jeffrey pine seeds from Jeffrey pine/antelope bitterbrush vegetation in western Nevada. From a bait station seed source, 0.5% of radioactively-labeled seeds were eaten and 98.1% were cached. The average number of seeds in cheek pouches ranged from 18.5 to 29.9 based on 4 yellow-pine chipmunks. There were 36 to 91 caches made with 3 to 9.9 seeds. Caches were separated by distances of 4.6 to 16 feet (1.4-4.9 m). Transport distance ranged from 8.5 to 195 feet (2.6-59.3 m) and averaged 82 feet (25 m). Yellow-pine chipmunks typically cached seeds more than 16 to 33 feet (5-10 m) from the source and only "sparingly" cached in areas with thick pine needle litter [192]. In the same study area using similar methods, Vander Wall [195] found that seeds were moved farther in a mast (x=87.9 feet (26.8 m)) than in a nonmast (x=68.2 feet (20.8 m)) year. Often seeds were moved from primary caches to secondary or up to sixth-order caches. Recaching was 3 times more common in a nonmast than in a mast year. In a mast year, the highest order cache was 3, and in a nonmast year was 6 [195].

Dispersal of Jeffrey pine seed was affected by habitat in the Whittell Forest and Wildlife Management Area. Radioactively labeled Jeffrey pine seed was scattered to simulate seed dispersed by wind from 2 source trees. Source tree 1 occurred in a forest clearing with deep soils and low herbaceous and litter cover. Source tree 2 was in a sparsely forested site with thin soils, boulders, and rock outcrops. There were 1,064 seeds/source tree, and 95% or more were removed within 43 hours. Three percent or less were consumed. Most caches were small, with 1 to 4 seeds, but caches with up to 35 seeds were found. The distance between caches and source tree 1 ranged from 4.3 to 178 feet (1.3-54.2 m), and from source tree 2 the distance ranged from 20 to 206 feet (6.2-62.9 m). Yellow-pine chipmunks were the most common harvesters [189]. Yellow-pine chipmunk caching was twice as probable in antelope bitterbrush habitats and 1/6th as likely in Jeffrey pine forests than expected based on the proportion of these habitats available (P<0.001). In antelope bitterbrush habitats, over 50% of caches were in the open (>4 inches (10 cm) from shrub), 12% to 16% were under shrub canopy, and 28% to 35% were at the canopy edge. Most caches (66-73%) were in mineral soil, 24% to 27% were in light litter (<5 mm thick), and 3% to 7% were in thick litter (>5 mm). In the Jeffrey pine forests, a high proportion of caches (63-100%) were under mature tree canopies of 75% to 86% closure and in thick (2-4 inches (5-10 cm)) plant litter [190].

Clark's nutcrackers disperse and bury Jeffrey pine seeds, and unrecovered caches are important to successful seedling germination and establishment. On the eastern slopes of the Sierra Nevada in Mono and Madera counties, Jeffrey pine seed harvesting began in early to mid-September, and seed was stored from mid-September through mid-October. Clark's nutcrackers assessed seed quality from the sound made when shaken against their mandibles, ensuring that sound seeds were cached. They used their bills to dig shallow trenches a few centimeters long, where 1 to 15 seeds were cached. Caches were often made at tree bases, near rocks, and in other sites where snow melt was early. Open pumice substrates were preferred over pine needle litter as cache sites. Caches were 4 to 120 inches (10-300 cm) apart [180]. For additional information on the utilization of Jeffrey pine by Clark's nutcracker, see Birds.

Seed banking: Jeffrey pine seed banks are predominantly unrecovered animal caches. Substrate and environmental conditions affect cache recovery. Field experiments conducted in the Whittell Forest and Wildlife Management Area showed that increased moisture levels increased the success of yellow-pine chipmunks and deer mice in finding caches made by other individuals. When conditions were dry, animal subjects were much less likely to recover caches other than their own [194]. However, dry conditions that may hamper cache recovery would not likely be conducive to seed germination.

In a laboratory study, yellow-pine and long-eared chipmunks trapped from the Carson Range in Washoe County, Nevada, found just 2.3% of caches made in ash, while they found 98% of caches in sand. When chipmunks were allowed to cache seed themselves, the average number of caches made in ash was significantly more than caches made in sand (P=0.02). Researchers suggested that seeds were likely located by smell with more ease in sand than in ash, and that caching in ash may have been an attempt to decrease pilfering [16].

Germination: Jeffrey pine seed germinates readily in the spring [64], and while stratification may not be necessary [77,168] it can decrease the time required for successful germination [168]. The best germination is said to occur in mineral soils in full sun conditions [103]. Seed burial and cache site selection by small mammals and Clark's nutcracker can improve the emergence success of Jeffrey pine seed.

Temperature and stratification: Stratification of Jeffrey pine seed from northeastern California decreased germination time. Seed was air dried and stored at 30 °F (1 °C) for 2 to 3 years before being stratified for 3 months at 40 °F (5 °C). At a temperature of 77 °F (25 °C), stratified seeds reached 50% germination after 3 days and unstratified seeds after 23 days. As germination temperatures decreased, the differences in germination rates of stratified and unstratified seeds increased. At 59 °F (15 °C), 50% germination was reached after 6 days for stratified and after 115 days for unstratified seed. At 40 °F (5 °C), 50% germination was reached after 50 days for stratified and after 175 days for unstratified seed [168]. Long-term storage of Jeffrey pine seed collected from Lassen National Forest did not affect germination rates. Germination of fresh seed averaged 65% after 3 months of stratification at 40 °F (5 °C), and seed stored for 8.5 years averaged 67% when stratified at same temperature [109].

Seed/cone size: Percent germination decreased with seed size, which related to cone size (see Seed Production), on the eastern slope of the Sierra Nevada in Lassen County. Germination was most rapid for the largest seeds from the largest cones and slowest for the smallest seeds from the smallest cones. Germination period differed by 2 weeks for large and small seeds [110].

Cached seed: Emergence is typically more successful when seeds are buried in caches than when unburied. A multitude of experiments have investigated the fate of seeds from caches in western Nevada. When seeds were buried to mimic yellow-pine chipmunks caches and protected from small mammals, 55.2% of buried seed emerged. Just 1 of 100 seeds left on the soil surface produced seedlings. Burial by ant activity likely aided germination of the seed on the soil surface [189].

Germination and seedling emergence were affected by cache site environment and substrate in western Nevada. Emergence from rodent caches was greatest at mid- and low-elevation sites, but seedling survival was best at mid- and high-elevation sites. Emergence of seeds planted in an exclosure did not differ between shade and full sun conditions (P≥0.1) at any elevation [47]. For a discussion of climate differences at these low-, mid-, and high-elevation sites, see Climate.

Charles Webber © California Academy of Sciences

While canopy cover did not affect seeds in exclosures, it affected emergence from scatter-hoard caches in open Jeffrey pine/antelope bitterbrush plots. About 50% of seedlings emerged in open sites over 4 inches (10 cm) from the nearest shrub, 20% emerged beneath shrub canopies, and 29% emerged at shrub canopy edges. More seedlings emerged at the canopy edges than in the open based on the proportion of the habitats available (P<0.001). There were 48 to 528 emergence sites/100 m². Seedlings emerged singly, in clumps of 2 to 7, and less commonly in large clusters of up to 54. Excavations of random emergence sites revealed that nearly 9% of cached seeds failed to emerge. Emergence sites were concentrated on mineral soil (75%), but litter was low in the general study area [188]. Seedling survival is discussed in Seedling establishment/growth below.

Jeffrey pine seedling establishment may be greatest on burned sites with exposed mineral soil. Seedling emergence from artificial caches of depths of 0.2 and 1 inch (5 mm, 25 mm) was significantly greater on burned than unburned plots (P=0.002) in pine forests near Lake Tahoe. Seeds planted in ash 1 month after fire produced 14.8 times more seedlings than seeds planted on unburned plots. Caches made in soil produced 3.5 to 8.5 times more seedlings than caches in pine needle litter on the soil surface. Seed removal rates were lower on burned than unburned sites for 1 to 5 months after fire, and seedlings on burned sites survived 1.9 times longer than on unburned sites [17]. For additional information on seedling establishment on burned sites, see Seed caches on burned sites.

Seedling establishment/growth: Jeffrey pine seedling survival may be affected by canopy cover, weather patterns, associated species, and/or pest infections. Jeffrey pine regeneration is not considered rapid or reliable [64]. Likely a combination of these factors limits and/or encourages recruitment in any year.

Canopy cover: In mixed-conifer forests on the Teakettle Experimental Forest, Jeffrey pine seedlings (≤19 inches (49 cm)) and saplings (≥20 inches (50 cm)) were under open canopies. In the study area, Jeffrey pine seedling density averaged 10/ha and was 0.4% of the total conifer seedling composition. There were 4 saplings/ha, which was 0.9% of the total conifer sapling composition. Jeffrey pine seedling and sapling densities in whitethorn ceanothus-dominated patches were slightly greater than 10/ha, and in closed-canopy forests were less than 10/ha. Most Jeffrey pine seedlings and saplings occurred in dry, open areas with high light levels. Most seedlings (>50%) grew in forest floor litter, but a little more than 20% grew in mineral soil [42,120].

Weather: Jeffrey pine seedling establishment was associated with precipitation on the Teakettle Experimental Forest and Lassen National Forest. However, annual precipitation analyses were used in the Experimental Forest study, and seasonal precipitation was used in the National Forest study, making comparisons difficult. In the 3,200-acre (1,300 ha) Experimental Forest study area, Jeffrey pine recruitment was associated with wet years (Palmer Drought Severity Index was 2.36). Nearly all Jeffrey pine established before 1865 in wet years during or shortly before an El Niño year [119]. In Lassen National Forest meadows, establishment of Jeffrey pine was most likely when spring temperatures were cool and summer precipitation was below normal. Establishment was least likely when spring temperatures were normal. On 4 meadows, there were 1.8 to 204.5 Jeffrey pine seedlings, 1.8 to 47.3 saplings, and 18 to 166 trees. Seedlings, saplings, and trees were counted along downslope transects ranging from 140 to 960 feet (43-290 m) from forest to meadow [118].

Associated species: Antelope bitterbrush was a nurse plant to Jeffrey pine seedlings in western Nevada, and woolly mule-ears interfered with Jeffrey pine seedling establishment in eastern California.

Nurse plants: Antelope bitterbrush was important to Jeffrey pine seedling survival in Nevada's Whittell Forest and Wildlife Management Area. Mortality of seedlings established in the spring of 1989 was 85% by the fall of 1990. Single seedlings became increasingly common with each successive sampling season due to deaths within seedling clumps. Single seedlings survived at a significantly higher rate than clumped seedlings (P<0.05), and herbivore browsing was more common on clumped than single seedlings (P<0.05). Most mortality (62%) was due to summer desiccation. Mortality rates were greatest on plots with the greatest forb and cheatgrass (Bromus tectorum) densities. Single seedlings under antelope bitterbrush canopies survived significantly better than seedlings in the open (P<0.001), and seedling clumps under shrub canopies had significantly greater potential of producing at least 1 survivor than did clumps in the open (P<0.001). Increased seedling survival under antelope bitterbrush was likely due to decreased temperature, lower moisture stress, and herbivory protection. It is unknown if canopy cover benefits seedlings over 2 years old [188].

Interference/allelopathy: Jeffrey pine seedling survival and growth were greater on montane chaparral than woolly mule-ears-dominated sites on the east slope of Boca Hill near Truckee, California. One-year-old seedlings grown from locally collected seed were planted in the spring of 1978 and evaluated 5 and 8 years later. Survival was significantly greater 5 and 8 years later (P<0.005 and P<0.02, respectively) in montane chaparral than in woolly mule-ears vegetation. Seedling height was also significantly greater 5 and 8 years later (P<0.005 and P<0.001, respectively) in montane chaparral than in woolly mule-ears vegetation [126].

Other studies have investigated possible reasons for decreased survival and growth of Jeffrey pine in woolly mule-ears vegetation. In the laboratory, seeds watered with woolly mule-ears root and leaf extracts had significantly less radicle growth (P<0.01 and P<0.05, respectively) than seeds watered with distilled water. Jeffrey pine seeds stratified in woolly mule-ears vegetation in the Sagehen Basin had significantly less radicle growth (P<0.01) than seeds stratified in areas free of woolly mule-ears litter. Germination was also lower for seeds stratified on sites with woolly mule-ears litter than on sites without litter and for seeds watered with root and leaf extracts than for seeds watered with distilled water. Jeffrey pine roots in areas with woolly mule-ears had less mycorrhizal infection than did roots grown without woolly mule-ears, which may have affected regeneration success [213]. Other researchers suggested that neither allelopathy nor soil nutrients affected Jeffrey pine seedling growth in woolly mule-ears sites in the northern Sierra Nevada of Plumas County. Jeffrey pine seed germination and seedling growth were compared in soils collected from early-seral, woolly mule-ears-dominated sites, midseral, shrub-dominated sites, and late-seral Jeffrey pine-dominated sites. Germination was not significantly different by soil type and averaged about 95%, although early-seral soils had the lowest organic horizon depths and lowest levels of carbon, calcium, and magnesium. After 417 days, seedlings in early- and midseral soils had more mass than those in late-seral soils [137].

Dwarf mistletoe: In California, dwarf mistletoe (Arceuthobium spp.) can cause heavy mortality in Jeffrey pine seedlings and saplings. Twenty percent fewer seeds germinated from infected than uninfected Jeffrey pine trees, and seedlings produced from infected tree seed were deemed less "vigorous" than those from uninfected tree seed [74].

Growth: Growth of Jeffrey pine seedlings, saplings, and trees is reported from a variety of studies and sites. Growth and survival can be affected by canopy cover and stand density. In a greenhouse study, the relative growth rate of Jeffrey pine seedlings between 2 and 10 weeks old averaged 26.6 mg/g/day. A maximum growth rate of 38.5 mg/g/day was reported [44]. In old-growth mixed-conifer forests of the Lake Tahoe Basin, importance of Jeffrey pine saplings over 5.9 inches (15 cm) tall, but under breast height was positively correlated with Jeffrey pine canopy cover (P<0.0005). There was no negative correlation with other canopy tree species [8].

Radial stem growth of Jeffrey pine averaged 20 μm/day at elevations of 7,900 to 8,900 feet (2,400-2,700 m) on the Kern Plateau of the southern Sierra Nevada. Growth was averaged over size class, site, and year. Total annual radial growth averaged 1.4 mm/year. Jeffrey pine had measurable radial stem growth for an average of 66 days. The growing season increased significantly on south slopes (P<0.001). Sapling growth was proportional to daily maximum and average daily temperatures (P<0.005), but this was not true for large Jeffrey pines [141]. Small Jeffrey pines (<16 inches (40 cm)) were most common at low elevations (5,090 to 5,710 feet (1,550-1,740 m)) on the Carson Range of western Nevada. Most large trees occurred at mid- (6,560-6,730 feet (2,000-2,050 m)) or high elevations (7,495-8,020 feet (2285-2445 m)). Tree density was usually greatest at midelevation sites. The number of dead trees was highest (19/ha) at low-elevation sites. At mid- and high-elevation sites the number of dead Jeffrey pine averaged 2.8/ha and 2.6/ha, respectively. Average radial growth rates of trees older than 30 years was positively correlated with elevation and negatively correlated with tree density (=0.420, P<0.001). Mid- and high-elevation Jeffrey pine growth rates were 54% and 62% greater, respectively, than low-elevation growth rates [47].

Vegetative regeneration: Jeffrey pine does not sprout from adventitious buds or spread through vegetative means. However, regrowth of needles from surviving terminal buds can occur following crown scorch [121]. For more on this, see Terminal bud regrowth.

SITE CHARACTERISTICS:
Jeffrey pine occupies habitats from the edges of moist, high-elevation meadows to the borders of arid deserts [48], but is often dominant on dry, infertile sites throughout its range [64]. Montane forests above the ponderosa pine zone are typical Jeffrey pine habitat [32].

Climate: Short growing seasons, drought, and cold are tolerated by Jeffrey pine [63]. Throughout the Jeffrey pine range, average January temperatures range from 9 to 36 °F (-13 to 2 °C). Day and nighttime temperatures in July may differ by 47 °F (26 °C) in the Klamath Mountains and on eastern slopes of the Cascade Range and Sierra Nevada. Winter precipitation contributes most to the average annual precipitation in Jeffrey pine habitats. Annual precipitation levels are lowest on eastern slopes of the Cascade Range and Sierra Nevada and range from 15 to 17 inches (380-430 mm). Annual precipitation averages are much greater at elevations of 4,170 to 4,990 feet (1,270-1,520 m)) in the Klamath Mountains and on the western slopes of the Sierra Nevada. Average snow fall can be less than 30 inches (760 mm) on low-elevation sites in the Klamath Mountains and greater than 200 inches (520 cm) in high-elevation Sierra Nevada habitats [64].

Climate and growing conditions in Jeffrey pine habitats can vary considerably with elevation. In the Carson Range of western Nevada, annual precipitation levels based on 25 years of records averaged 23.3 inches (591.8 mm) at low, 29.3 inches (744.2 mm) at mid-, and 44 inches (1,118 mm) at high elevations. During a 2-year period, the average maximum temperature was about 16 °F (9 °C) higher at low- than high-elevation sites. Average daily maximum soil temperatures varied only about 5 °F (3 °C) between low- and high-elevation sites [47]. For a short discussion of germination and seedling emergence at these sites, see Cached seed. In Jeffrey pine habitats in Baja California Norte, low-elevation sites averaged 12 to 20 inches (300-500 mm) of annual rainfall, and high-elevation sites averaged about 24 inches (600 mm). Snow was possible from December to February at high elevations. June through August were hottest and driest [130].

Cold tolerance: Jeffrey pine is considered more drought and cold tolerant than ponderosa pine based on site occupancy differences [48]. However, Wagener [200] observed no mortality differences in young or old ponderosa pine and Jeffrey pine after extremely cold weather in California. In sympatric populations, mortality of ponderosa pine was less than Jeffrey pine. The researcher suggested that if cold tolerance differences exist between the species, they occur in the seedling stage or that cold causes damage other than mortality. For more on differences and similarities between Jeffrey pine and ponderosa pine, see Haller [48].

Jeffrey pine buds and leaves from 1-year-old twigs on 10- to 40-year-old trees collected in midwinter from California resisted injury at temperatures as low as -22 °F (-30 °C). Twig tissue resisted damage at -58 °F (-50 °C) [145].

Elevation: Throughout its range, Jeffrey pine primarily occupies sites from 490 to 9,500 feet (150-2,900 m) [63]. Jeffrey pine is most common above the ponderosa pine zone [32].

Jeffrey pine elevational range by state and region
State Elevation (feet)
California 1,500-10,600 [54,112] most common at 6,000-9,000 [112]
Nevada 5,000-7,800 [69]
Oregon 1,200-6,000 [3]
Baja California Norte 1,500-9,500 [104,130,211]
Region
North Coast and Klamath Ranges
(on serpentine outcrops)
as low as 200 [85]
Slate Creek Valley of the Inyo National Forest found trees at 10,000-11,000 [21]
Sierra Nevada 5,000-9,000 [85]
northern Sierra Nevada 4,990-6,000 [143]
southern Sierra Nevada 6,990-8,990 [143]
southern California 3,600-6,600 [107]
San Bernardino Mountains 5,400-9,800 [102]
Traverse and Peninsular ranges 4,500-9,800 [85]

Soils: Jeffrey pine typically grows on shallow, rocky, infertile soils [63] and survives on dry pumice and bare granite substrates [81]. About 20% of Jeffrey pine's distribution occurs on ultramafic soils; the rest occurs on volcanic and granitic parent materials [64]. In southwestern Oregon and northwestern California, Jeffrey pine is most typical of ultramafic soils, including serpentine [2,5,22]. Kruckeberg [76] considers Jeffrey pine a "faithful" indicator of serpentine soils at low to moderate elevations in northwestern California and southwestern Oregon. Kruckeberg also suggests that the main Jeffrey pine range is on nonserpentine soils, but that outlier populations are often restricted to serpentine soils [76].

The following paragraph provides more descriptive reports of the soils common in Jeffrey pine habitats throughout its range. Douglas-fir-Jeffrey pine forest types in the North Umpqua and Tiller Ranger Districts of southern Oregon occupy sites with shallow (x=15.7 inches (40 cm)), coarse-textured soils [4]. On eastern slopes of the Sierra Nevada, Jeffrey pine is most common on decomposed granites [76]. Jeffrey pine vegetation associations in upper montane habitats of central and southern Sierra Nevada occupy moderately deep to deep (x=32-39 inches (81-99 cm)) sandy to loamy soils with granitic or volcanic origins [133]. The incense-cedar-Jeffrey pine cover type in Humboldt Redwoods State Park occurs on shallow serpentine soils [205]. In Lassen Volcanic National Park, Jeffrey pine-white fir forests occurred on sites with higher pH (x=5.9) and greater basic cation (K, Ca, Mg) exchange capacity than other forest types [124]. In the western Great Basin of Nevada, Jeffrey pine is restricted to soils derived from hydrothermally altered andesite. Altered soils have lower pH, calcium, and phosphorus than unaltered soils, which are dominated by big sagebrush. A lack of competing vegetation on these soils likely allows Jeffrey pine to tolerate the average annual precipitation of 262 mm/year, normally considered outside its tolerance range [26,27]. For a detailed description of soil composition and chemistry of Jeffrey pine stands in the Little Valley of Nevada, see Johnson [66]. Soils in Jeffrey pine-mixed conifer forests in the Sierra San Pedro Mártir are shallow, well to excessively drained, and strongly acidic (pH x=5.3). Organic matter averaged 2.3% in surface soils, and coarse-textured fragments averaged 26.5%. For more on soil nutrient composition, see Stephens and Gill [164].

SUCCESSIONAL STATUS:
Jeffrey pine is shade intolerant [7,63] and typically replaced by shade-tolerant conifers in the absence of canopy-opening disturbances [106,172]. On exceptionally harsh sites, Jeffrey pine may be a climax species [2,129].

Climax: Jeffrey pine forests restricted to ultramafic soils in the upper Illinois River drainage of Siskiyou Mountains in southwestern Oregon were considered an edaphic climax type [2]. In the Sierra San Pedro Mártir, Jeffrey pine/mountain snowberry vegetation is characterized as a "supramediterranean climax forest" [129].

Primary succession: In Lassen Volcanic National Park, a single Jeffrey pine occurred on a 10-year-old volcanic mudflow, highlighting its tolerance of early-seral conditions. Findings suggested that Jeffrey pine was more tolerant of early-seral, disturbed sites than of white fir competition and late-seral conditions. Jeffrey pine frequency and density were greater on 300-, 750-, and 1,500-year avalanche flows than in nearby white fir-dominated climax forests. On most flows, Jeffrey pine density was greatest on those plots closest to a seed source [52]. In another study of debris flows created by the 1915 eruption of Lassen Peak, Jeffrey pine colonization of mud flows was continuous from at least 1940 to the date of the study (1987) [75].

Succession without fire: Numerous studies have investigated stand changes that occur in Jeffrey pine habitats in the absence of fire. Decreased Jeffrey pine recruitment, decreased Jeffrey pine importance, increased Jeffrey pine mortality, increased stand density, increased shade-tolerant conifer importance, and increased canopy closure are commonly described as succession proceeds without fire in mixed-conifer and/or Jeffrey pine-dominated stands.

Using historic photos, journals, and other sources, researchers found that decreased fire frequency together with timber harvests and intense grazing changed the composition and structure of northeastern California's eastside pine forests. Jeffrey pine and ponderosa pine forests studied in the late 1980s had greater small tree density, increased canopy closure, greater shrub density, more dead and downed material, more litter and duff, decreased stand age, reduced tree spacing, lower stand height, and less herbaceous vegetation than in presettlement time (~1850). The forest stand structure and fuel availability of forests in the late 1980s would likely support more severe fires than occurred in presettlement time [88].

Before fires were excluded in Lassen Volcanic National Park and the adjacent Caribou Wilderness, fires burned an average of every 11 years in Jeffrey pine habitats (Swanson 1980, cited in [61]). Frequent fires maintained disclimax Jeffrey pine and ponderosa pine forests by preventing the establishment of climax fir (Abies spp.) species. An abundance of fire-scarred Jeffrey pine and ponderosa pine in the area suggested that past fires burned quickly and with low intensity. Frequent low-severity fires maintained an open structure and uneven age distributions. Without fire, shrubs and white fir increase in the understory, providing ladder fuels that support crown fires [61].

In the Warner Mountains of extreme northeastern California, a lack of Jeffrey pine and ponderosa pine recruitment was attributed to thick litter and decreased sunlight due to increased white fir density. Changes in stand structure that were considered barriers to Jeffery pine and ponderosa pine recruitment were thought to be a result of fire exclusion and heavy grazing [184].

Contemporary Jeffrey pine-white fir forests had significantly greater Jeffrey pine density and basal area (P<0.05) and significantly smaller diameters (P<0.05) than presettlement (pre-1850) forests on the eastern shore of Lake Tahoe. Contemporary forests reflect postlogging succession during a long fire-free period (>120 years). Presettlement forests were reconstructed from stumps cut in early 19th century, and contemporary forest characteristics came from current stand measurements. White fir density in contemporary forests was about 3 times that of presettlement forests, and the diameter of white fir trees was significantly smaller in contemporary than presettlement forests [172].

In the San Bernardino Mountains, tree density increased in mixed Jeffrey pine, mixed white fir, and monotypic Jeffrey pine forests after 60 or more years of fire exclusion. Small-diameter tree importance increased and large-diameter tree importance decreased without fire. In mixed Jeffrey pine forests, average tree density was 93 stems/ha in 1929, and stands had heterogeneous diameter structure. Sixty-three years later, tree density was 167 stems/ha, dominance of juvenile trees increased, and the density of large trees (>26-inch (67 cm) DBH) decreased. In mixed white fir stands, there were 174 trees/ha in 1929 and 246/ha in 1992. Over this period, trees with DBH of 4.7 to 13 inches (12-33 cm) nearly tripled, and the number of large trees decreased by half. White fir was the overwhelming dominant, which was not the case in 1929. Jeffrey pine forests in 1929 were open and had heterogeneous diameter distributions. After fire exclusion, density of white fir and incense-cedar increased, and overall tree density increased by 114%. Stems with DBH measurements less than 26 inches (67 cm) increased, and stems with DBH over 39 inches (100 cm) decreased. Tree density increases were less dramatic in Jeffrey pine forests occupying dry, high-elevation sites. The fire-return interval during the fire exclusion period was estimated at 700 years [106].

When Jeffrey pine-white fir forests with different fire management were compared in the San Bernardino Mountains of southern California and in La Corona Arriba in Baja California Norte, forests subject to fire exclusion in the San Bernardino Mountains had more Jeffrey pine mortality, nearly double the adult tree density, and more live and dead tree basal area than those in La Corona Arriba. Forests in the San Bernardino Mountains did not burn for about 90 years, while there was no policy of fire exclusion in La Corona Arriba. There were significantly more standing dead Jeffrey pine in southern California than in Baja California (P<0.05), and mortality was primarily a result of severe drought conditions and bark beetle attacks in southern California. Weather data from Big Bear Dam indicated that the lowest precipitation levels on record were for 2 years in the late 1990s. Researchers suggested that the density and basal area differences between the 2 sites were due to decreased fire frequency in the San Bernardino Mountains, and that increases in tree density and basal area increased the forest's susceptibility to drought and insects [146]. When Jeffrey pine forests in the San Bernardino Mountain sites were compared to those in Sierra San Pedro Mártir in Baja California Norte, findings were similar. Adult tree density and basal area in the San Bernardino Mountains were nearly double that of the Sierra San Pedro Mártir. Most sites in the San Bernardino Mountains had not burned since 1905. There were 3 times as many standing dead Jeffrey pine and white fir in southern California as in Baja California. Most trees in southern California established in the last 100 years; the maximum age of Jeffrey pine was around 285 years in southern California, whereas the oldest Jeffrey pine tree in the Sierra San Pedro was 448 years old [147].

Succession after logging: Jeffrey pine cover increased with time since clearcut logging in red fir forests of the central Sierra Nevada, and Jeffrey pine growth increased on thinned, mixed ponderosa pine-Jeffrey pine stands in northeastern California's Black Mountain Experimental Forest. Cover of Jeffrey pine was significantly higher in 11- to 32-year-old than in 4- to 10-year-old clearcuts (P<0.05) in red fir forests. Cover averaged 0.04%, 1.6%, and 1.9% in 4- to 10-year-old, 11- to 25-year-old, and 26- to 32-year old clearcuts, respectively [31]. After 55-year-old ponderosa pine-Jeffery pine stands in northeastern California were thinned from about 11,000 trees/acre to around 700 trees/acre, pine tree height on thinned stands was 62% and DBH was 167% of unthinned stands 5 years after treatment. Twelve years after treatment, tree height was 38% and DBH was 43% greater on thinned than unthinned stands. Thirty years after treatment, tree height was 39% and DBH was 91% greater on thinned than unthinned stands [92].

SEASONAL DEVELOPMENT:
Female cones develop shortly after male cones, and fertilization of Jeffrey pine occurs about 13 months after pollination [64]. Female cones are pollinated from May to July, cones ripen from August to September of their second year, and seeds are dispersed from September to October [49,77,112,211]. Trees at low-elevation sites often shed pollen earlier than trees at high-elevation sites [29]. Phenological development of 10 young Jeffrey pine trees (3-6 feet (0.9-2 m) tall) on sites at about 5,300 feet (1,600 m) on the western slope of Sierra Nevada in the Stanislaus National Forest was monitored for 7 to 8 years. The average date that growth began was 16 May. The growing season averaged 78 days, and the average minimum number of days to reach 50% of total annual growth was 21 [36].

FIRE ECOLOGY

SPECIES: Pinus jeffreyi
FIRE ECOLOGY OR ADAPTATIONS:
Fire adaptations: Jeffrey pine resists fire kill through a variety of structural and physiological adaptations. Rapid taproot growth and early development of insulating bark offer protection to Jeffrey pine seedlings and young trees [61]. Jeffrey pine is considered moderately fire resistant as a sapling (2-4 inch (5-10 cm) DBH) and highly resistant as an adult [99]. Thick bark, protected terminal buds, self-pruning branches, open crowns, and high moisture content of needles minimize Jeffrey pine fire damage [61]. There is some speculation that deep bark fissures may be a fire adaptation [197]. Jeffrey pine's ability to shed burning bark scales as a means to reduce fire damage has received mention in the literature [81], and firefighters have reported observing fires extinguished by shedding bark scales [197]. Bark shedding processes have not been tested experimentally [81].

Bark thickness: Jeffrey pine bark is often described as thick; however, bark thickness measurements are rarely reported. Using regression analyses, bark thickness of saplings with a 2-inch (5 cm) DBH was estimated at 0.18 inch (0.46 cm). Jeffrey pine adults with a 48.8-inch (124 cm) DBH had an estimated bark thickness of 2.6 inches (6.5 cm) [62]. From 50 Jeffrey pine trees with an average DBH of 21 inches (53 cm) on Mt Pinos in southern California, bark thickness averaged 2.1 inches (5.3 cm) [197,198].

Terminal bud survival: Terminal buds that survive fire can produce new needles in the first postfire year. On several burned sites in the Sierra Nevada, researchers monitored 44 trees that had complete crown scorch and foliage consumed on more than 50% of the tree height. Half of these trees produced new needles in the first postfire year [121].

Seedling establishment: Jeffrey pine seedling establishment is improved in canopy gaps created by fire, where mineral soil is exposed and light levels are high [72]. Seedlings on burned sites come from seed from surviving or nearby unburned mature Jeffrey pine trees [72], fire-scorched trees [199,201], and/or seed-caching animals [16,17]. Wagener [199,201] reported that "exceedingly good stands of seedlings" came from fire-scorched trees on burned sites in California.

Fire regimes: Jeffrey pine occurs in many habitats and with a variety of other species throughout its range. While low-severity surface fires are common in open-canopy forests with limited understory fuels, increased forest densities and an increased presence of ladder fuels in the understory fuel higher-severity fires. On a landscape scale, a mixed-severity fire regime occurs in Jeffery pine habitats.

Fuels: Fuel types and arrangements as they relate to fire behavior in Jeffrey pine forest types have been described in many areas. Both small and large fires are possible, but low- to moderate-severity surface fires were historically common in Jeffrey pine vegetation. However, in many areas fire exclusion has increased fuel loads and produced ladder fuels that may support larger, more severe fires than was common under historic fire regimes. Western dry pine and mixed-conifer forests were "shaped by stand-maintenance fire". Before around 1850, low-severity, frequent surface fires fueled by grasses, shrubs, small trees, needles, and fallen braches rarely killed thick-barked species like Jeffrey pine. Even in times of increased temperatures and decreased moisture, fires could be large but were not necessarily severe [18].

In open old-growth Jeffrey pine stands in the Lassen Fire Management Area, fuels were primarily loose needles, grasses, cones, scattered fallen branches, and bark pieces. Fuel accumulations were often heavier in dwarf mistletoe-infested areas because of fallen witches' broom and dead trees [61]. On the southern slope of Mt Pinos, widely spaced Jeffrey pine and a discontinuous understory fueled small fires that produced a mosaic of small, even-aged tree groups. Lightning-ignited fires on Mt Pinos averaged less than 4 acres (2 ha) in size. Researchers noted that fire exclusion has led to increased densities of "spindly, sapling-size Jeffrey pine" [197,198]. The Jeffrey pine/curlleaf mountain-mahogany vegetation type on top of rocky volcanic substrates in northeastern California was "nearly fire proof" due to landscape position and a lack of fuels [157]. For more specific details regarding fuels, fuel types, and fuel loadings, see Fire Management Considerations.

Ignitions: Lightning is a common ignition source in many Jeffrey pine forests, and southern California sheepherders referred to Jeffrey pines as "lightning trees". Seventeen years of modern lightning records in north-central Baja California suggest that anthropogenic ignitions were likely before 1950. The large number of spring fires and low levels of spring lightning suggested that lightning was not likely the sole ignition source [30].

On Mt Pinos, pine forests may experience 600 lightning strikes/summer, and single storms have produced over 100 lightning strikes. Lightning strikes can create "sleeper" trees that burn internally until the fire is extinguished, creeps out into dry fuels, or the tree ignites. Wiggins (personal communication in [197]) reported that sheepherders working in southern California advised against camping under Jeffrey pines or "lightning trees", and later that day a Jeffrey pine tree in his camp was struck by lightning [197]. From a random sample of 277 Jeffrey pine trees on the upper southern slope of Mt Pinos, 32.5% had lightning damage [198].

In Lassen Volcanic National Park there were 302 lightning-ignited fires in the summers from 1931 to 1981. There were an average of 7 lightning fires/year. Occasionally, a single dry lightning storm started 6 or 7 fires. Most fires were small (<0.25 acres (0.1 ha)), but larger fires (≥300 acres (120 ha)) occurred at 8- to 10-year intervals [169]. Between 1913 and 1989, there were more than 5,000 lightning ignitions recorded in the Modoc National Forest (Cavasso, personal communication in [88]). For an in-depth discussion on lightning: types of lightning strikes that are most likely to cause ignition, typical delay of fire activity following lightning strikes, most commonly struck features within western forests, tree damage or mortality from lightning strikes, and indirect mortality from forest pests attracted to lightning-damaged trees, see Taylor [175].

Fire severity: Low-severity fires are described in most qualitative Jeffrey pine fire literature, but Jeffrey pine forests have experienced fire severities ranging from low-severity surface fires to severe, stand-replacing surface and crown fires. In the northern Sierra Nevada, stand-replacing fires occurred even before the practice of fire exclusion, but crown fires were less common than moderate- and low-severity fires [144]. The 2002 Biscuit Fire in southwestern Oregon burned 14.4% of Jeffrey pine forests in the area: 5.3% burned severely, 7.6% burned at moderate severity, and 1.5% burned with low severity. Low-severity fires lightly scorched the vegetation, killed only a few large trees that were present on the burned site, and consumed very small diameter fuels. Moderate-severity fires killed 40% to 80% of trees, consumed most litter and fine ground fuels. High-severity fires killed nearly 100% of trees [6].

The McNally Fire burned about 97,214 acres (39,341 ha) of Jeffrey pine forests in the Sequoia National Forest in the summer of 2002. About 6% of the area was unburned, 24.5% burned at low severity, 49% was moderately burned, and 21.6% burned severely. Unburned patches had less than 10% canopy cover change. On low-severity burned sites, crown scorch affected less than 40% of the canopy, and mortality occurred in seedling and sapling size classes. Moderately burned sites had 40% to 89% canopy crown scorch, but most overstory trees survived. Severely burned sites had more than 89% canopy scorch, and understory mortality was complete. The Manter Fire in the southern Sierra Nevada burned approximately 13,610 acres (5,508 ha) of Jeffrey pine forest in the summer of 2000. Low-severity, moderate-severity, and high-severity fires burned 24.5%, 43.6%, and 31.9% of the Jeffrey pine forests, respectively. The northern Sierra Nevada Storrie Fire burned 41.7% of a 316-acre (128 ha) Jeffrey pine forest at low severity in the summer of 2000. Moderate- and high-severity fires burned 52.8% and 5.6% of Jeffrey pine forests, respectively. All burned sites had not burned for an extended period, as long as 125 to 150 years on some sites [121].

The majority of Jeffrey pine and mixed Jeffrey pine forests burned at low severity in 1989 summer fires in the Sierra San Pedro Mártir of Baja California Norte; however, stand-replacing fires occurred as well. Whether stand-replacing fires were a result of crown fire, severe surface fire, or a combination was not determined from the aerial photographs and vegetation maps used to assess fire damage. In the northern portion of the study area, the total area burned in Jeffrey pine forests was 770.7 acres (311.9 ha): 39% burned in low-severity surface fires, 26.8% in high-severity surface fires, and 34.2% in stand-replacing fires. Stand-replacing fires occurred primarily in areas surrounded by chaparral vegetation and at elevations below 5,200 feet (1,600 m). In northern mixed Jeffrey pine forests, 861.4 acres (348.6 ha) burned, 51.3% in low-severity surface fires, 27.9% in high-severity surface fires, and 20.8% in stand-replacing fires. In southern Jeffrey pine forests, 1,800 acres (729 ha) burned, 70.2% in low-severity surface fires, 23.1% in high-severity surface fires, and 6.7% in stand-replacing fires. Fire severity ratings were based on percentage of canopy cover remaining after fire: low-severity surface fires produced <10% canopy mortality, high-severity surface fires produced over 10% canopy mortality, and stand-replacing fires killed more than 90% of the canopy [101].

Fire-return intervals: Once scarred by a fire, Jeffrey pine trees easily develop scars from subsequent fires, making them excellent fire recorders and extremely valuable in fire history studies [161]. Fire history studies from Jeffrey pine habitats span the entire range of the species. Most of these studies are summarized in the table below. Average fire-return intervals were typically lower in ponderosa pine- or Jeffrey pine-dominated forest types than in mixed-conifer- or white fir-dominated forest types. In a review of fire history studies in Jeffrey pine forests, Skinner and Chang [152] found fire-return intervals were more variable in upper montane than in low-elevation, pine-dominated forests, and that fire-return intervals in Jeffrey pine forests were more variable than those in ponderosa pine forests, although site conditions and fire frequency were similar. Reviewers suggested that fire frequency variability in Jeffrey pine forests may have been due to a limited fire season, slow fuel accumulations, and occupation of landscapes broken up by rocky outcrops [152].

Historic and contemporary fire-return intervals in Jeffrey pine habitats by study area. Superscripts indicate data collected and used in analyses: see legend below.
Study area
Vegetation type Time period (approximate) Fire-return interval(s) (FRI); calculation method, if provided Notes
Klamath Province, southwestern Oregon2 [209]
Jeffrey pine/huckleberry oak-pinemat manzanita 1840-1950 x=7.3 years fire frequency decreased after 1950 with fire exclusion [209]
Jeffrey pine/huckleberry oak-pinemat manzanita-dwarf silktassel 1529-1950 x=24.8 years
Jeffrey pine-incense-cedar/huckleberry oak 1422-1950 x=10.6 years
Jeffrey pine-incense-cedar/whiteleaf manzanita 1620-1950 x=11.2 years
Upper montane and subalpine basins in Scott Mountains of Klamath Range1 [151]
mixed conifer 1376-1941 x=54.5 years, range=5.8-276 years no fires from 1950 to 1995 in any basin; fires frequent, mostly small sized, likely low to moderate severity [151]
Southern Cascades, northeastern California1,3 [117,118]
open ponderosa pine-Jeffrey pine 1700-1849 7-49 years for widespread fires (≥7 units in 700 km² study area); 2-22 years for moderate-sized fires (≥4 units); a fire 1 unit in 93 of 150 years conditions wetter/cooler than average 3 years before most widespread fires (P<0.05); most widespread fires in El Niño years; conditions wetter/cooler than average (P<0.05) before nonfire years [117]; fire frequency significantly (P<0.001) lower from 1906-1996 than 1750-1905; 1 fire after 1910 [118]
Prospect Peak in Lassen Volcanic National Park1,3 (2,630-ha study area) [170]
Jeffrey pine (1,855 to 2,100 m) 1656-1849a x=4.9 years (composite) 66.9% of fires in dormant season; fire size from 1627-1904: x=241 ha, range=39-742 ha; x FRI significantly different (P<0.05) between 1656-1904 and 1905-1994; x FRI on east < south < west slopes
1850-1904a x=5.2 years
1905-1994b x=89 years
Jeffrey pine-white fir (1,840-2,220 m) 1656-1849 x=7.5 years 82.5% of fires in dormant season; fire size from 1627-1904 x=195 ha, range 6-666 ha; x FRI on east < south < west slopes [170]; comparisons of presettlement and contemporary forests available in Succession without fire
1850-1904 x=4.9 years
1905-1994 not given
Prospect Peak, Lassen Volcanic National Park1,2,3 [173,174]
Jeffrey pine pre-1900 x=16 years, range=9.5-32 years 30% of fires in growing season; x FRI on east < west ≈ south slopes
white fir-Jeffrey pine x=29.8 years, range=15.5-38 years x FRI on east <west ≈ south slopes
Caribou Wilderness at southern tip of Cascade Range1,2,3 (950-ha study area)
white fir-Jeffrey pine (density and basal area of white and red fir >Jeffrey pine) (2,060-2,360 m) 1735-1874 x=70 years (point) 29% low- (>75 stems/ha remaining), 46% moderate- (25-75 stems/ha), 25% high- (<24 stems/ha) severity fires
Thousand Lakes Wilderness¹,²,³
white fir-Jeffrey pine pre-1900 x=14 years, range=7-25 years 4% low-, 44% moderate-, 52% high-severity fires [173,174]
Thousand Lakes Wilderness1,2,3 (2,042-ha study area) [10]
white fir-Jeffrey pine 1710-1995 x=4 years, range=1-20 years (composite); x=14 years, range=7-25 years (point) 4% low-, 44% moderate-, 52% high-severity fires; x fire size 145.7 ha, range 34-388 ha
1710-1849 x=5.8 years
1850-1904 x=5.1 years
1905-1995 too few intervals to compare
white fir-sugar pine (Jeffrey pine common) 1658-1995 x=9 years, range=2-35 years (composite); x=15 years, range=7-43 years (point) 2% low-, 35% moderate-, 63% high-severity fires; x fire size 103 ha, range 12-335 ha [10]
1658-1849 x=11.3 years
1850-1904 x=10.8 years
1905-1995 too few intervals to compare
west-slope Carson Range, east-slope Lake Tahoe1 (6,000-ha study area) [171]
Jeffrey pine-white fir (1910-2300 m) 1650-1850 x=3.4-9.4 years (for 8 watersheds), range=1-36 years; range for widespread fire (≥6 watersheds)=3-31 years 90% dormant-season fires; no fires after 1871; from 1775-1850 widespread fires in driest years (P<0.01), fires in ≥2 to ≥6 watersheds preceded by 2-4 years wet weather (P<0.01); high moisture associated with nonfire years [171]
Little Frying Pan drainage in Sweetwater Mountains of eastern CA1 (<40-ha study area) [45]
Colorado pinyon-western juniper (Pinus edulis-Juniperus occidentalis) 1687-1895 x=8 years "low-intensity" fire likely; from 1960-1996 fire size <0.1 ha; woody fuel buildup with lack of fire has increased crown fire potential in extreme weather [45]
Yosemite National Park (prescribed fire natural areas) [186]
Jeffrey pine 1972-1993 x=158 years 0.06% of Jeffrey pine forests burned in prescribed natural fires from 1972-1993, fire size 4-400 ha [186]
Valentine Camp Natural Reserve¹ [161]
Jeffrey pine 1745-1889 x=9 years, range=4-17 years last fire before 1900, but remains fairly open Jeffrey pine-dominated canopy; fires more frequent in Jeffrey pine than in red fir only 100 m away (P<0.05) [161]
Dinkey Creek Watershed in southern Sierra Nevada1 (>2,070-ha study area, six 1.4-ha plots) [131]
mixed conifer 1771-1873 x=3.2-5.4 years (by plot), range=1-12 years high incidence of lightning, from 1911-1964 were 39 lightning-ignited fires (1/1.4 years), no fire >2.5 ha from 1911-1964 [131]
Kings Canyon National Park1 (160-ha study area) [206]
yellow pine (Jeffrey pine and ponderosa pine) 1775-1909 x=3.5 years, x=11.4 years/individual tree no fire after 1909 [206]
Teakettle Experimental Forest1 (1,300-ha study area) [119].
old-growth mixed conifer (white fir dominant, but Jeffrey pine largest and tallest) 1614-1917 x=17.4 years (point), range=3-115 years 10 widespread fires from 1795-1865, after 1865 only 2 localized fires; greater number of fires in La Niña years (P<0.001) but proportion burned not different in La Niña years (P=0.77) [119].
1692-1865 x=11.4 years (composite, minimum 3 scars)
San Bernardino Mountains1 [96]
Jeffrey pine pre-1860 x=14 years FRI significantly (P<0.05) longer from 1905-1974 than earlier time periods, ignitions primarily lightning [96]
1860-1904 x=19 years
1905-1974 x=66 years
San Bernardino Mountains (68 plots) [106]
Jeffrey pine and Jeffrey pine-white fir pre-fire exclusion x=15-30 years stand structure and composition changes without fire discussed in Succession without fire [106]
1929-1992 x=700 years
San Bernardino Mountains (45 plots of 10 × 30 m) [89]
Jeffrey pine and Jeffrey pine-white fir pre-1905 x=16 years [89]
1905-1980 x=38 years
San Bernardino Mountains [97]
Jeffrey pine 1760-1904 x=12 yearsa different subscripts, significantly different (P<0.05); annual area burned from 1940-1950 was 2,385 ha, from 1960-1970 was 1,528 ha [97]
1905-1967 x=29 yearsb
Sierra San Pedro Mártir, Baja California Norte1 (~0.8 km²/forest type) [165]
Jeffrey pine-mixed conifer 1700-1799 x=5.8-9.6 years (composite mean range from 1 fire scar to 3 fire scars and ≥25% of recording trees) 1% dormant-season, 42% early earlywood, 32% middle earlywood, 16% late earlywood, and 9.4% latewood scars
1800-1899 x=9.2-22 years
1900-1997 x=8-15.3 years
Jeffrey pine 1700-1799 x=3.9-10.1 years 52% early earlywood, 30% middle earlywood, 11% late earlywood, and 8% latewood scars

Overall, fires scarring >10% of trees occurred when precipitation was low (P<0.01) and 2 previous years were wet (P<0.01, 1st year; P<0.05, 2nd year); possible causes of increased FRI after 1800s: livestock grazers reducing fine fuels and limiting fire spread and size, reduced size of native populations that burned landscape, and/or climate changes [165]

1800-1899 x=6-13.4 years
1900-1997 x=6.3-23.5 years
Sierra San Pedro Martir2,4,5 (40,655 ha) [101]
Jeffrey pine 1925-1990 x=45 years 436 fires < 16 ha, 41 fires > 800 ha and 2 fires>6,400 ha in size; long FRI attributed to slow fuel buildup and litter accumulation [101]
Jeffrey pine-white fir x=62 years
1Fire scars, 2age class distributions, 3radial growth, 4aerial photos, and 5vegetation and fire maps.

Jeffrey pine occurs in a variety of habitats, many of which may not be listed in the above table. For additional information on fire regimes that may be relevant to Jeffrey pine, consult the table below:

Fire regime information on vegetation communities in which Jeffrey pine may occur. For each community, fire regime characteristics are taken from the LANDFIRE Rapid Assessment Vegetation Models [79]. These vegetation models were developed by local experts using available literature, local data, and/or expert opinion as documented in the PDF file linked from the name of each Potential Natural Vegetation Group listed below. Cells are blank where information is not available in the Rapid Assessment Vegetation Model.
Pacific Northwest California Great Basin
Pacific Northwest
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Northwest Woodland
Pine savannah (ultramafic) Replacement 7% 200 100 300
Surface or low 93% 15 10 20
Ponderosa pine Replacement 5% 200    
Mixed 17% 60    
Surface or low 78% 13    
Subalpine woodland Replacement 21% 300 200 400
Mixed 79% 80 35 120
Northwest Forested
Mixed conifer (southwestern Oregon) Replacement 4% 400    
Mixed 29% 50    
Surface or low 67% 22    
California mixed evergreen (northern California) Replacement 6% 150 100 200
Mixed 29% 33 15 50
Surface or low 64% 15 5 30
Red fir Replacement 20% 400 150 400
Mixed 80% 100 80 130
California
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
California Shrubland
Montane chaparral Replacement 34% 95    
Mixed 66% 50    
California Woodland
Ponderosa pine Replacement 5% 200    
Mixed 17% 60    
Surface or low 78% 13    
California Forested
Mixed conifer (North Slopes) Replacement 5% 250    
Mixed 7% 200    
Surface or low 88% 15 10 40
Mixed conifer (South Slopes) Replacement 4% 200    
Mixed 16% 50    
Surface or low 80% 10    
Jeffrey pine Replacement 9% 250    
Mixed 17% 130    
Surface or low 74% 30    
Interior white fir (northeastern California) Replacement 47% 145    
Mixed 32% 210    
Surface or low 21% 325    
Red fir-white fir Replacement 13% 200 125 500
Mixed 36% 70    
Surface or low 51% 50 15 50
Sierra Nevada lodgepole pine (dry subalpine) Replacement 11% 250 31 500
Mixed 45% 60 31 350
Surface or low 45% 60 9 350
Great Basin
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Great Basin Shrubland
Wyoming big sagebrush semidesert with trees Replacement 84% 137 30 200
Mixed 11% >1,000 20 >1,000
Surface or low 5% >1,000 20 >1,000
Mountain big sagebrush with conifers Replacement 100% 49 15 100
Montane chaparral Replacement 37% 93    
Mixed 63% 54    
Mountain shrubland with trees Replacement 22% 105 100 200
Mixed 78% 29 25 100
Curlleaf mountain-mahogany Replacement 31% 250 100 500
Mixed 37% 212 50  
Surface or low 31% 250 50  
Great Basin Woodland
Juniper and pinyon-juniper steppe woodland Replacement 20% 333 100 >1,000
Mixed 31% 217 100 >1,000
Surface or low 49% 135 100  
Ponderosa pine Replacement 5% 200    
Mixed 17% 60    
Surface or low 78% 13    
Great Basin Forested
Aspen with conifer (low to midelevation) Replacement 53% 61 20  
Mixed 24% 137 10  
Surface or low 23% 143 10  
Aspen with conifer (high elevation) Replacement 47% 76 40  
Mixed 18% 196 10  
Surface or low 35% 100 10  
*Fire Severities: Replacement=Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Surface or low=Any fire that causes less than 25% upper layer replacement and/or removal in a vegetation-fuel class but burns 5% or more of the area.
Mixed=Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects [50,78].

POSTFIRE REGENERATION STRATEGY [167]:
Tree without adventitious buds and without a sprouting root crown
Crown residual colonizer (on site, initial community)
Initial off-site colonizer (off site, initial community)

FIRE EFFECTS

SPECIES: Pinus jeffreyi

 

  © Br. Alfred Brousseau, Saint Mary's College of California

IMMEDIATE FIRE EFFECT ON PLANT:
Adult Jeffrey pine often survives low-severity surface fires. However, mature Jeffrey pine mortality has been observed after prescribed fire in areas with accumulated litter or duff and/or woody ladder fuels [207]. Severe surface and crown fires can kill Jeffrey pine.

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
Jeffrey pine survival can be affected by tree size and fire timing. Survival likelihood is increased if Jeffrey pine is burned while dormant; trees are more vulnerable when actively growing [199,201]. Jeffrey pine is considered fire resistant as a 2- to 4-inch (5-10 cm) DBH sapling and highly resistant as an adult [99].

Wagener [199,201] observed Jeffrey pine trees on 29 burned sites in California and reported on burned tree and postfire characteristics that affected survival. Survival was more likely when trees were "young", "vigorous", and occupied "good" sites. Trees with heavy cone crops were sometimes more susceptible to mortality than equally damaged trees without cone crops. Trees with extensive crown scorch did not necessarily sustain severe bud damage, and often postfire crown growth 1 year after fire was much greater than 1 month following fire. Wagener noted that in most cases, more than 50% bud survival was necessary for tree survival. Live crown percentages were useful in predicting survival of fire-scorched Jeffrey pine, and postfire weather and insect conditions also affected survival [199,201]. The table below summarizes the levels of cambium, crown, and foliage injury that Jeffrey pine can sustain and yet likely survive.

Percentage of cambium, crown, and foliage injury that "vigorous" Jeffrey pine trees on "above-average" sites burned by late-season (after 1 August) fires can sustain and still be expected to survive [201]
Modifications to tree "vigor", site quality, and fire season Cambium injury

Live crown¹
%

Green foliage²
%

None none-light ≥50 ≥10
Increased cambium injury moderate (cambium kill <25% of circumference not >stump height, may be some narrow strip kill) ≥50 ≥20
Below-average site condition none-light ≥50 ≥15
Midseason fire none-light ≥50 15-25 or more
Low prefire "vigor", small crowns none-light ≥60 ≥15
¹Proportion of original crown in which twigs and buds are still alive after fire (includes parts bearing green or partially green foliage).
²Proportion of green or partially green needles present regardless of crown location.

PLANT RESPONSE TO FIRE:
Scorched Jeffrey pine on burned sites may regrow needles if terminal buds are not killed, and seedling establishment from surviving adult trees, adjacent unburned sites, and/or seed caching animals is likely on burned sites.

Terminal bud regrowth: Severely scorched trees sometimes produce new green growth from surviving terminal buds protected by scales [121,199,201]. On burned sites in the Sierra Nevada, half of 44 trees with 100% crown scorch and incinerated foliage on less than 50% of the tree produced new foliage in the first postfire year [121].

Seedling establishment: Jeffrey pine seedling establishment is improved in canopy gaps created by fire, where mineral soil is exposed and light levels are high [72]. Survival of seed in fallen cones is not reported on burned sites. Jeffrey pine seeds in a test tube were killed after exposure to 210 °F (100 °C) temperatures for 0.5 hour [168]. Seedlings on burned sites come from seed from surviving or nearby unburned mature Jeffrey pine trees [72], fire-scorched trees [199,201], and/or seed-caching animals [16,17]. Wagener [199,201] reported that "exceedingly good stands of seedlings" came from fire-scorched trees on burned sites in California. Additional information on Jeffrey pine seed dispersal and seedling establishment on burned sites is presented below.

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
Survival/mortality: Throughout California, survival of Jeffrey pine decreased with increased fire severity and fuel loadings. Low-severity fires typically produced low Jeffrey pine mortality. All 4 Jeffrey pine trees monitored after a severe fire in Cuyamaca Rancho State Park, California, died within 1 year of the fire. The study area had not burned for 95 years or more, and forests had more white fir and incense-cedar and greater stem density than they did before fire exclusion [159]. Just a single Jeffrey pine tree died after an October prescribed fire on Spooner Summit in Lake Tahoe Basin. Prefire and postfire fuel loadings were 5.1 and 4.9 tons/acre, respectively. Of the 245 Jeffrey pine trees marked before the fire, 26 suffered complete crown scorch but 1 year after fire had green growth. However, researchers predicted some additional postfire mortality from insect attacks and drought. Dendroctonus valens and Ips pini together attacked 31% of burned Jeffrey pine trees, and 53% and 12% of Jeffrey pine trees were attacked by D. valens and I. pini alone, respectively [39]. Less than 3% of the total canopy was killed in the Starr King Fire, which burned south of Yosemite Valley in mixed Jeffrey pine, red fir, and western juniper vegetation. The fire burned from 4 August to 3 October; fire intensity was very low in the first 10 days. Between 29 August and 9 September, fire size nearly doubled. Fireline intensity estimated beneath Jeffrey pine ranged from 29.49 to 539.48 BTU/s/foot. Downed Jeffrey pine logs and snags burned "intensely" [185].

Seed caches on burned sites: Researchers found that chipmunks preferred to cache seeds in ash and that seedlings from caches on burned sites survived longer than those on unburned sites. In the laboratory, long-eared and yellow-pine chipmunks from the Carson Range in Washoe County, Nevada, located 98% of artificial caches made in the sand but just 2.3% of caches made in ash. When chipmunks were provided seed to cache themselves, the average number of caches made in ash was significantly greater than the number made in sand (P=0.02). Researchers suggested seeds in sand were easier to locate by smell than seeds in ash, and ash caching may have reduced stealing or pilfering by others [16]. Seeds from artificial caches on pine-dominated burned sites near Lake Tahoe, Nevada, produced 14.8 times more seedlings than those on unburned plots (P=0.002). The rate of seed removed by animals on burned sites was lower than on unburned sites for 1 to 5 months after fire. Caches in soil produced 3.5 to 8.5 times as many seedlings as caches made in pine needle litter on the soil surface [17].

Postfire seedling establishment: Often Jeffrey pine seedling abundance is greater on burned than unburned sites. Fire severity and/or season can affect Jeffrey pine seedling establishment [71], and seedling recruitment on burned sites can continue for many years after fire [13]. Not all studies reported Jeffrey pine increases following fire [71,95,119], and successful seedling establishment on burned sites may be gradual. Likely postfire growing conditions, fire severity, and seed source availability affect the rate and success of Jeffrey pine seedling establishment.

Jeffrey pine seedling densities were greater 2 years after than before spring prescribed fires but reduced from prefire densities 2 years after fall prescribed fires in mixed-conifer forests on the Quincy Ranger District of the Plumas National Forest. Spring fires produced greater fireline intensities than did fall fires, suggesting that increased fireline intensity produced better sites for seedling establishment. However, Jeffrey pine seedling density also increased between the prefire and second postfire sampling seasons on unburned plots. Likely differences in fire intensity and spring and fall growing conditions affected seedling establishment [71]. For more information on this study, consult the Research Project Summary Plant response to prescribed burning with varying season, weather, and fuel moisture in mixed-conifer forests of California.

The number of Jeffrey pine seedlings on 5-year-old burned sites was substantially greater than on unburned mixed-conifer sites in northern California. The 1960 Donner Ridge Fire was an escaped slash pile fire that burned in mid-August. Fire severity was not described. In 1965, there were 496 Jeffrey pine seedlings (<0.8 inch (2 cm) DBH) on the 20-acre (8 ha) burned site and just 1 on the unburned site [12]. Burned and unburned sites compared 7 and 14 years after this fire showed a much higher density of Jeffrey pine seedlings and saplings on the burned than on the unburned site. Mature trees were much more abundant on unburned than burned sites, suggesting that the fire was severe enough to produce mortality in Jeffrey pine trees [13].

Density of mature, immature, and seedling Jeffrey pine on 7- and 14-year old burned and unburned plots (each 20 acres) [13]
Postfire year 7 14 unburned
Mature (>20 cm DBH) 0.5 0.6 10.1
Immature (>5 years old and <20 cm DBH) 5.4 36.6 38.1
Seedling (≤5 years) 28.6 3.3 0.1

Jeffrey pine recruitment was associated with moisture availability but not recent fire in old-growth, mixed-conifer stands on the Teakettle Experimental Forest. Jeffrey pine recruitment was associated with wetter years (Palmer Drought Severity Index was 2.36). Just 17% of Jeffrey pine recruitment occurred 1 to 4 years after fire. Almost all Jeffrey pine established before 1865 in wet years during or shortly before an El Niño year. Researchers suggested that low-severity fires on the dry, shallow soils occupied by Jeffrey pine may not have produced favorable seedbed conditions [119].

Fire severity effects: In the studies summarized below, postfire Jeffrey pine recruitment was most abundant on sites burned in stand-replacing fires; however, the sites burned in stand-replacing fires were evaluated 10 and 19 years after fire. Sites burned in "light intensity" fires did not have abundant Jeffrey pine recruitment 2 years after fire. A lack of multiple postfire studies with similar postfire sampling dates makes assessing recruitment and mortality differences between fire severities and seasons difficult.

Density of Jeffrey pine seedlings (<2 inch (5 cm) DBH)) and saplings (2-8 inch (5-20 cm DBH)) was typically much lower on burned than unburned sites 2 years after "light intensity" prescribed fires in Cuyamaca Rancho State Park. Mature Jeffrey pine mortality was limited. Fires occurred in mixed-conifer-Jeffrey pine-California black oak woodlands with chaparral-dominated understories. The Paso Picacho site burned in April, and the Granite Springs and Oakzanita sites burned in December. On the Paso Picacho site, the density of large Jeffrey pine trees on burned sites was more than 3 times that of unburned plots. Jeffrey pine saplings were absent from burned plots, and the seedling density on burned plots was nearly half that of unburned plots. On the Granite Springs site, there were more large Jeffrey pine trees on burned than unburned plots. It is unlikely, however, that large trees were produced on burned sites, and likely differences between burned and unburned sites existed before the fires. Sapling and seedling densities on burned plots were significantly lower than on unburned plots (P<0.01 and P<0.02, respectively). On the Oakzanita site, Jeffrey pine tree, sapling, and seedling densities were greater on unburned than burned sites [95]. For additional information on this study, see the Research Project Summary Response of vegetation to prescribed burning in a Jeffrey pine-California black oak woodland and a deergrass meadow at Cuyamaca State Park, California.

A fall prescribed fire in the Tharp Creek Watershed of Sequoia National Park produced 16.7% and 21.7% average annual Jeffrey pine mortality on 2 white fir-mixed conifer sites monitored for 5 years after fire. Mortality was concentrated in the subcanopy. The fire burned from 23 to 26 October 1990. Relative humidity during the day was 21% to 30% and at night was 30% to 40%. Fuel moisture levels in the litter and duff averaged 28%. For 100-hour and 1,000-hour fuels, moisture levels were 14% and 64%, respectively. At the time of ignition, air temperatures were 50 to 61 °F (10-16 °C) and winds were calm. The fire was a combination of backing and strip head fires with flame lengths of 0.16 to 7.9 feet (0.05-2.4 m). One-hour, 10-hour, and 100-hour fuels were reduced by 96%, 77%, and 60%, respectively. Tree (≥4.6 feet (1.4 m)) mortality was evaluated before and after fire as well as from an unburned reference site. On unburned sites, there was no Jeffrey pine mortality. Between 1 and 5 years after the fire, most tagged Jeffrey pine in the subcanopy (below main canopy) and nearly half in the codominant canopy (part of main overstory canopy) were dead. None of the tagged Jeffrey pine trees in the dominant canopy (above codominant canopy) was killed. Researchers indicated that drought conditions 3 years before and 2 years after the fire may have contributed to mortality in the larger size classes. Basal area changes were also monitored before and after the fire. Compared to the unburned control site, Jeffrey pine basal area increased by an average of 0.27% and 0.42% on the 2 burned sites before the fire. From 1989 to 1994 (includes 1 year of prefire data), Jeffrey pine basal area was reduced by 6.5% and 10% on the 2 burned sites compared to the unburned site [115]. For more information, see the entire Research Paper by Mutch and Parsons [115].

The relative densities of Jeffrey pine saplings and seedlings were much greater and mature tree relative densities much lower on sites burned 10 to 19 years ago than on sites burned between 60 and 100 years ago in stand-replacing fires. Burned areas were upper montane white fir-Jeffrey pine-mixed-conifer forests in the Lake Tahoe Basin. In aerial photos of the Angora Ridge dated to 1917 and 1940, shrubs dominated. A forest canopy was developing in 1976, although there were still shrub-dominated patches. Domestic sheep grazing in the area may have affected vegetation recovery on Angora Ridge that burned 100 years before this study [144].

Relative density of Jeffrey pine trees, saplings, and seedlings on sites burned in stand-replacing fires between 10 and 100 years ago [144]
  Angora Ridge Cathedral Creek Cascade Lake Luther
Approximate time since fire (years) 100 60 19 10
Mature trees 8.5 21 0 0
Saplings (<61 cm tall) 4.7 16 91 14
Seedlings (<10 cm in diameter) 0 1 100 17

Delayed mortality: Mortality of Jeffrey pine trees may continue for several years on burned sites, and often postfire insect attacks further weaken damaged trees causing additional delayed Jeffrey pine mortality. After a small June prescribed fire in ponderosa pine-Jeffrey pine forests in Lassen Volcanic National Park, all 14 ponderosa and Jeffrey pine trees (>18 inches (46 cm) in diameter)) died. The first tree died 2 years after the fire, while most others died 3 years after the fire. Fire burned on a relatively steep slope. Other plots burned in September did not kill all Jeffrey pine trees. Potential causes of delayed mortality were not discussed [87]. On the north shore of Lake Tahoe, the presence of bark beetles on Jeffrey pine was compared on sites burned in prescription fires and unburned mixed-conifer forest plots. The fire produced variable effects on individual trees. Of 389 Jeffrey pine trees evaluated, crown scorch averaged 33%, and bole char height averaged 2.6 feet (0.79 m). A year after the fire, bark beetle attacks were more numerous on burned than unburned Jeffrey pine trees. Burned Jeffrey pine trees had a 24.8 times greater chance of bark beetle attack. Crown scorch and bole char height both had positive relationships (P=0.0001) with bark beetle attack probability. Small trees were preferred by red turpentine and Ips beetles but were not consistently chosen by Jeffrey pine beetles [15]. After a small lightning-ignited fire in a mixed pine forest in Shasta County, California, adult Arhopalus asperatus were observed on the most severely scorched Jeffrey pine trees. Jeffrey pine trunks were scorched up to 20 feet (6 m). Insect activity decreased with time since fire [210].

FIRE MANAGEMENT CONSIDERATIONS:
Prescribed fire is often used in Jeffrey pine habitats. The following sections provide information on surface and aboveground fuel characteristics and potential prescribed or wildfire behavior in Jeffrey pine vegetation.

The timing and severity of prescription fires in Jeffrey pine habitats depend on management goals and site conditions. Increased fire severity typically increases seedling establishment but can kill adult trees. Stand density is closely related to fire severity. Dense forests will likely fuel more severe fires than open-canopy forests. Fire may also be used to manipulate species composition in Jeffrey pine habitats. Fir trees are less likely to survive fire than Jeffrey pine, and cover of small-diameter firs can be reduced by low-severity fires. Clearly defined management goals, an understanding of site and stand conditions, and a well-designed prescription fire will produce the best results in the fire management of Jeffrey pine.

Fuels: Characteristics of fuels typical of Jeffrey pine habitats including needles, cones, litter, duff, small- and large-diameter stems, and snags are described from a large portion of Jeffrey pine's range.

Needles and cones: Jeffrey pine needles dry rapidly, ignite easily, and support fire spread [1]. A fuelbed (35×35 cm, <2 inches (5 cm) tall), created from Jeffrey pine needles collected near Lake Tahoe, Nevada, produced a maximum flame height of 34 inches (87 cm) after being dried to 1.5% to 2.7% moisture. Average flame time was 64.7 seconds, and burn time averaged 391.4 seconds. Average combustion was 90.1%, and average rate of weight loss was 35.3 μg/s. Mean flame height produced by the Jeffrey pine fuelbed was the highest of all 13 western conifer species tested. Flame time was lowest of all species tested, and percent combusted was second to ponderosa pine. Based on the reported values, surface fires could be supported by Jeffrey pine needle litter, and rapidly and nearly complete combustion of surface fuels would be likely [33]. Findings were similar for other Jeffrey pine needle fuel beds tested [35]. The maximum flame length produced after 10 Jeffrey pine cones with 2.3% fuel moisture collected from the Tahoe Basin were burned in a fire chamber was 31 inches (80 cm). Flame and smolder times averaged 262 seconds and 4,412 seconds, respectively. Cone burn time averaged 4,674 seconds, and combustion averaged 89%. Cones burned almost completely to white ash. Flame length, smoldering time, and burn time produced by burning Jeffrey pine cones were the longest of the 9 pine species tested [34].

Surface and aboveground fuels: Fuel bed characteristics were averaged in 4 Jeffrey pine stands from the central Sierra Nevada. Stands were monocultures of Jeffrey pine saplings (1-4 inch (2.5-10 cm) DBH), pole-size (4-24 inch (10-60 cm) DBH), mature (24-47 inch (60-120 cm) DBH), or old (>47 inch (120 cm) DBH) Jeffrey pines. Litter and duff depths averaged 0.4 inch (1.1 cm) and 2 inches (5.4 cm), respectively. Litter and duff weight averaged 8.965 kg/m². Woody fuel weight averaged 0.025 kg/m² for the 0- to 0.25-inch (0.64 cm) size class; 0.196 kg/m² for 0.25- to 1-inch (0.64-2.54 cm) size class; and 0.073 kg/m² for the 1- to 3-inch (2.54-7.62 cm) size class. There were no woody fuels in the over 3-inch (7.62 cm) size class [187].

Litter and duff fuel loads were much greater and 1,000-hour fuel loads much less in Jeffrey pine forests from the southern California Valentine Camp Natural Reserve than Jeffrey pine forests in the Sierra San Pedro Mártir National Park. The 2 areas differed in fire management. Fires have not been excluded from the Sierra San Pedro Mártir like they have in southern California. A summary of the fuel loadings and canopy cover differences in the 2 sites is given below [161,162]. For additional information on these sites and their differences in stand structure and fire management, see Fire-return intervals and Succession without fire.

Average fuel loads (SE) of Jeffrey pine forests in the Valentine Camp Natural Reserve and Sierra San Pedro Mártir National Forest
  1-hour fuels 10-hour fuels 100-hour fuels 1,000-hour fuels litter and duff layer canopy closure

t/ha

%, measured with densiometer

Sierra San Pedro Mártir National Forest, Baja California Norte [162] 0.11 (0.03) 0.85 (0.16) 1.20 (0.27) 13.64 (3.84) 8.69 (no duff) 40.1
Valentine Camp Natural Reserve, southern California [161] 3.13 (1.05) 1.78 (1.22) 28.38 (7.48) 44.4 [163]

In Jeffrey pine-mixed conifer forests of the Sierra San Pedro Mártir, almost 50% of plots had no coarse woody debris. Coarse woody debris was defined as wood on the forest floor, at least 3 feet (1 m) long, with a large-end diameter of at least 5.9 inches (15 cm). Average coarse woody debris load was 15.7 t/ha but ranged from 0 to 154.5 t/ha. Rotten coarse woody debris was more abundant than sound coarse woody debris. Large-end diameters ranged from 5.9 to 38 inches (15-96 cm), and most were less than 18 inches (45 cm). The very patchy coarse woody debris distribution may have been a chance occurrence or more likely was because debris was concentrated in unburned microsites protected from fire by topography or rocks [163]. See Snags and decay ecology for addition information on snags in Jeffrey pine habitats.

Fire behavior affected by fuel load: In the Blacks Mountain Experimental Forest, wildfire effects were studied in thinned, thinned and prescribed burned, and untreated ponderosa pine forests where Jeffrey pine was common. Before the treatments and the wildfire, there had been few fires in the area more than several acres in size since the early 1900s. Some thinned stands were burned in prescribed fires before the Cone wildfire in late September. Wildfire severity and postfire mortality (>90%) were greatest in untreated stands. Severe surface fires with some torching were common in the thinned stands and produced 40% to 60% mortality. Low-severity surface fire occurred in thinned and burned stands, with little mortality unless trees were adjacent to untreated stands [153]. Differences in early fall, late fall, early spring, and late spring prescribed understory fires in open, mixed Jeffrey pine, Douglas-fir, and incense-cedar forests on the Quincy Ranger District of the Plumas National Forest are described by Kauffman and Martin [70]. Prefire and postfire characteristics are provided. Fuel conditions, weather, fire behavior (heat combustion, spread rate, and flame length), fuel consumption, and postfire changes in litter, bare ground, and duff are described.

Burned and unburned soils: Many studies provide information on burned and unburned soils in Jeffrey pine forests. Blank and others [11] evaluate effects of a severe wildfire in Jeffrey pine forests that produced white ash on the soil surface are evaluated in comparisons of burned and unburned soils in Nevada's Toiyabe National Forest. Burned and unburned soils in the Little Valley area of the eastern Sierra Nevada were compared 20 years after a stand-replacing fire in a 100-year-old Jeffrey pine forest by Johnson and others [65]. In the Tahoe National Forest, forest floor nutrient contents and soil chemical properties were compared on prescribed burned, logged and slash burned, and unburned Jeffrey pine-dominated sites. See Murphy and others [113] for details. Soil nutrients and chemistry were described 2 months before and 1 year after the July Gondola wildfire in a mixed-conifer forest in the southeastern part of Nevada's Lake Tahoe Basin. For results of this study, see Murphy and others [114]. On the Teakettle Experimental Forest, soil temperatures, moistures, and respiration rates were evaluated on undisturbed, burned, thinned, burned and thinned mixed-conifer stands 2 years after disturbances by Concilio and others and Ma and others [23,93]. After a severe crown fire in Jeffrey pine-oak (California black oak and canyon live oak) woodlands, Goforth and others [41] compared the physical and chemical properties of ash and soils on burned and unburned sites. Soils from burned Jeffrey pine-oak woodlands were also compared to soils from burned mixed-conifer forests where tree densities averaged 5 times that of the woodlands.

Defensible space: Instructions for creating defensible space and for constructing a defensible house in wildfire prone mixed-conifer forests of the Incline Village/Crystal Bay area of Lake Tahoe are available from Smith and Adams [156]. Although instructions were designed for Incline Village/Crystal Bay, many provided suggestions are applicable to other wildland urban interface areas.

MANAGEMENT CONSIDERATIONS

SPECIES: Pinus jeffreyi
IMPORTANCE TO LIVESTOCK AND WILDLIFE:
American black bears, a variety of small mammals, many bird species, as well as insects, amphibians, and reptiles utilize Jeffrey pine habitats and/or feed on Jeffrey pine seedlings or seeds. Jeffrey pine seed feeders identified in the literature include California quail, northern flickers, American crows, Clark's nutcrackers, western gray squirrels, Douglas's squirrels, California ground squirrels, Heermann's kangaroo rats, deer mice, yellow-pine chipmunks, least chipmunks, Colorado chipmunks, lodgepole chipmunks, and Townsend's chipmunks [155]. In the Little Valley of western Nevada, yellow-pine chipmunks, golden-mantled ground squirrels, and Steller's jays gathered and cached Jeffrey pine seed. Golden-mantled ground squirrels scatter-hoarded Jeffrey pine seed, but often buried seeds too deep for successful germination. American black bears, quail, mule deer, mountain chickadees, nuthatches, and sparrows were common Jeffrey pine seed predators. Yellow-pine chipmunks were, however, the most effective Jeffrey pine seed dispersers. They often transported seeds to favorable germination and establishment sites, and their rapid removal of seeds decreased the chance of immediate predation [195]. If interested in more information on seed dispersal, caching, and on the eventual fate of cached Jeffrey pine seed, see sections on Animal dispersal, Clark's nutcracker dispersal, Seed banking, and Cached seed.

American black bears: There are observations of American black bears feeding on Jeffrey pine seeds and seedlings. Lanner [82] reports that when Jeffrey pine seeds are available, American black bears "lick up" large quantities. In Little Valley, American black bears fed on the tops of Jeffrey pine seedlings (Goodrich, personal communication in [188]).

Small mammals: Small mammals often cache and feed on Jeffrey pine seed. On the eastern slope of the Sierra Nevada in Mono and Madera counties, golden-mantled ground squirrels, chipmunks (Tamius spp.), and Douglas's squirrels fed on Jeffrey pine seeds [180]. In the northern Sierra Nevada, 10% of Townsend's chipmunks stomachs had small amounts of Jeffrey pine seed, and 6% of cheek pouches contained Jeffrey pine seed, although woody plant seed was scarce [177]. Jeffrey pine seedlings in south-central Oregon suffered 74.2% mortality over a 3-year period; mortality was primarily from winter feeding by pocket gophers [25].

Birds: Jeffrey pine provides food and habitat for birds. Cavity-nesting birds often utilize Jeffrey pine. In 3 years of study in eastside forests of Modoc, Lassen, and Shasta counties, 110 active nests were located, and all but 4 were in Jeffrey pine or ponderosa pine. Seventeen nests belonged to hairy woodpeckers, 16 to pygmy nuthatches, 12 to mountain chickadees, and 11 to red-breasted nuthatches. Researchers located Jeffrey pine snags with more than 8 nest holes, although trees with 8 or more nest holes were generally uncommon. Nesting was most common in dead trees with DBH of 16 inches (40 cm) or more, and nests were typically built 3 feet (10 m) or more above ground [86]. Researchers found 561 active cavity nests occupied by 18 species in the Sagehen Creek Field Station. Burned Jeffrey pine-white fir habitats were selected for nesting in significantly greater proportion than by chance based on habitat availability (P<0.05). Most nests were in snags (72%); 19% of nests were in dead tops of live trees; just 2% of nests were in live trees with intact tops. Sixteen of the 18 cavity-nesting species used Jeffrey pine for nesting. All western bluebird, 43% of Lewis's woodpecker, 38% of house wren, and 31% of American kestrel nests were in Jeffrey pine. Cavity-nesting birds foraged more in Jeffrey pine than expected based on availability [135]. There is additional information on Jeffrey pine snags in Snags and decay ecology.

Near the Cuyamaca Reservoir in San Diego County, acorn woodpeckers used many Jeffrey pine trees to store California black oak acorns. Acorns were stashed in cracks or in holes drilled in the bark. The researcher estimated that 13,200 acorns were stored in a single extensively used tree [140]. On the eastern slope of the Sierra Nevada in Mono and Madera counties, the following bird species fed on Jeffrey pine seeds: Williamson's sapsucker, hairy woodpecker, white-headed woodpecker, mountain chickadee, white-breasted nuthatch, Cassin's finch, red crossbill, and pine grosbeak [180].

Owls: Flammulated and California spotted owls utilize Jeffrey pine habitats. Flammulated owls in California are often found in ponderosa pine and/or Jeffrey pine forests. The flammulated owl breeding range is associated with the presence of Jeffrey pine and/or ponderosa pine [212]. In the Lassen National Forest, California spotted owls utilized mixed red fir, white fir, and Jeffrey pine forests for foraging. In the San Bernardino Mountains, Jeffrey pine trees used by nesting California spotted owls averaged 40 inches (100 cm) DBH, 116 feet (35 m) tall, and 233 years old. Averages came from 8 Jeffrey pine trees [46].

Clark's nutcracker: Jeffrey pine is an important food source for Clark's nutcracker in the Sierra Nevada. On the eastern slope of the Sierra Nevada in Mono and Madera counties, whitebark pine (Pinus albicaulis) and Jeffrey pine were the Clark's nutcracker's most important and productive food sources. Clark's nutcracker ate seed fresh and from recovered caches. Harvests of Jeffrey pine seed began in early- to mid-September in most years, but started by 1 August in one observation year. Stores of Jeffrey pine seed were made from mid-September through mid-October. Clark's nutcrackers quality-tested seed by rattling the seed against their mandibles to assess seed weight. Seeds were cached in shallow trenches dug and covered by the bill. Seeds from cones that remained on Jeffrey pine trees in the winter and midspring were also utilized by Clark's nutcracker [180]. On the Inyo National Forest, Clark's nutcrackers retrieved more of their caches in the spring and summer than would be expected by trial-and-error seaching. Caches were comprised primarily of Jeffrey pine seeds. Small mammal pilfering may have affected success rates [181]. For more on caches, see Clark's nutcracker dispersal.

Amphibians/reptiles: Pine, mixed-conifer, and conifer-oak forests that often include Jeffrey pine are important habitat for sensitive or threatened snakes and salamanders of southern California including the southern rubber boa, San Diego kingsnake, San Gabriel Mountain salamander, and the yellow-blotched salamander [166].

Insects: In mixed-conifer old-growth forests on the Teakettle Experimental Forest, cave crickets and pseudoscorpions were found most often or exclusively on Jeffrey pine trees. Jeffrey pine trees had high Simpson diversity, indicating an even distribution of small numbers of insect functional groups. Total abundance of arthropods on Jeffrey pine averaged 98 arthropods/kg of plant material [150].

Palatability/nutritional value: There was little information available on the palatability and nutrition of Jeffrey pine trees. Jeffrey pine seeds from Washoe County Nevada were 31.5% crude protein, 47.8% crude fat, 8% soluble carbohydrates, and 0.6% crude fiber [193].

Cover value: Jeffrey pine provides important habitat and likely important cover to several bird and mammal species. Information on use of Jeffrey pine as cover was integrated into Importance to Livestock and Wildlife.

VALUE FOR REHABILITATION OF DISTURBED SITES:
Jeffrey pine seedlings planted on reclaimed or decommissioned mine sites have been successful, and when a seed source is available, Jeffrey pine may natural colonize mine spoils. For additional information, see Hoover and others [56], Walker [202,203,204], and Butterfield and Tueller [19].

OTHER USES:
Jeffrey pine provided a food source and was used to treat pulmonary problems by early western people. The Paiute of Owens Valley and Mono Lake collected Pandora moth larvae from Jeffrey pine forests. Larvae were smoked, cooked, dried, and stored until eventually boiled and eaten at a later date [81]. Beginning in 1890, heptane distilled from Jeffrey pine was sold to treatment pulmonary problems and tuberculosis. Jeffrey pine heptane was also used to develop the octane scale used to rate petroleum used in automobiles (Mirov and Hasbrouck as cited in [90]).

Wood Products: Jeffrey pine is utilized for lumber. The wood is hard and strong [130].

OTHER MANAGEMENT CONSIDERATIONS:
Pests/diseases: Many pathogens and insects infect Jeffrey pine trees, but rarely is Jeffrey pine mortality attributed entirely to a single infection. Often harsh growing conditions cooccur with disease and insect outbreaks. In "pristine" mixed-conifer forests in the Sierra San Pedro Mártir, the overall incidence of diseases and insects on Jeffrey pine averaged 21%. Needle cast was the most common pathogen, and Jeffrey pine beetle the most common insect [94]. In long unburned mixed-conifer forests on the Teakettle Experimental Forest, Jeffrey pine mortality in the 8- to 20-inch (20-40 cm) DBH size class was significantly more than expected (P<0.05) based on the size class proportion in the area. Of trees in the high-mortality size class, mortality was significantly greater (P<0.05) in high tree density areas (x=1,000 trees/ha). Most mortality was related to pest or disease infections, and many trees had several types of infections. Researchers suggested that diseases and pests may function as the primary source of forest turnover when fire is excluded [158].

There are numerous potential Jeffrey pine root diseases. For the signs and symptoms of Jeffrey pine root diseases, possible management strategies, and impacts of fuel treatments, see Rippy and others [139]. Jeffrey pine is also a potential host to several dwarf mistletoe species, although western dwarf mistletoe (Arceuthobium campylopodum) is most common. Dwarf mistletoe is capable of causing "considerable damage" to Jeffrey pine [51]. In California, dwarf mistletoe may cause high levels of mortality in Jeffrey pine seedlings and saplings. Seeds from infected trees can have lower germination rates than seeds from uninfected Jeffrey pine trees, and seedlings from infected tree seed can be less "vigorous" than seedlings from uninfected tree seed [74]. For more on the identification and host preferences of mistletoes, see Hawksworth and others [51]. Dwarf mistletoe management options are described by Kimmey [74] and Scharpf and others [149]. Scharpf and others indicate that tree mortality is often a result of 2 or more pests, and all agents should be recognized and managed. For more on the insects and pathogens of Jeffrey pine forests, consult Jenkinson [64] and Parker and others [125].

Many researchers suggest that prior injury and/or stressful growing conditions increase the likelihood of subsequent Jeffrey pine infections and/or mortality [73,148], but not all researchers agree [57]. Pine engravers utilize Jeffrey pine as a host in some areas, but extensive mortality is rare. Researchers suggest that previously damaged trees, trees in dense stands, and trees suffering drought effects are often targeted by the pine engraver [73]. In South Lake Tahoe, California, Jeffrey pine mortality was greater with both Elytroderma fungal disease and Jeffrey pine beetle attacks than when trees were infected with either pest alone [148]. On the Susan River Watershed in Lassen National Forest, western and Jeffrey pine beetles did not preferentially attack weakened Jeffrey pine trees. More "apparently healthy" than weakened Jeffrey pine trees were attacked. The researcher noted that these results occurred in other areas as well [57].

Pollution: Jeffrey pine is susceptible to ozone damage. Greenhouse studies revealed damage and decreased growth in 2- to 3-year-old Jeffrey pine seedlings exposed to ozone [100,176]. Of 13 western conifer species exposed to ozone, Jeffrey pine × Coulter pine hybrids were most sensitive, and Jeffrey pine was third [100]. In Jeffrey pine stands in the Giant Forest region of Sequoia National Park, 90% of Jeffrey pine showed visible injury from ozone. Monthly averages of ozone were 30 to 70 ppb-hour over a year, and were highest during the growing season. Jeffrey pine recruitment was still occurring in all stands [128].

Climate change: Simulation modeling was used to predict changes in forest structure, composition, and fire regimes with projected future temperature and precipitation changes in the Sierra Nevada. Modeling indicated that species composition, forest biomass, fire frequency, and fire size changes were site specific. A general pattern was not described. For more information, see Miller [98].

Tree parameter estimations: Regression equations to estimate Jeffrey pine diameter, bark thickness, height, and crown width of Jeffrey pine are available. From Dolph [28], equations for estimating inside Jeffrey pine bark diameter and bark thickness are available for trees less than 81 years old on Sierra Nevada western slopes. Equations for estimating the height of Jeffrey pine from the Klamath Mountains using DBH are available from Garman and others [40]. Estimation equations to compute maximum crown width from DBH for Jeffrey pine in southwestern Oregon are provided by Paine and Hann [122].

Snags and decay ecology: Snag creation, breakage, fall, and decay rates have been studied in several Jeffrey pine forests from northern California to Baja California Norte. Jeffrey pine snags did stand for long periods when populations were monitored from 1975 to 1983 in second-growth Jeffrey pine- and white fir-dominated forests on the Sagehen Creek drainage. Jeffrey pine snags typically fell sooner than white fir snags, and small-diameter trees fell sooner than large-diameter trees. Researchers indicated that 75% of the Jeffrey pine snags (excluding the smallest size class) in the study area would fall after 11 years. Jeffrey pine snags decayed rapidly from 1978 to 1983. Of 224 Jeffrey pine snags that still had needles, twigs, and more than 20 limbs in 1978, 41% had no needles, twigs, and fewer than 20 limbs by 1983, and 40% had fallen. Of the new snags that formed during the same time period, 68% were Jeffrey pine, and 38% of the Jeffrey pine snags were less than 6 inches (15 cm) in DBH. Jeffrey pine beetles were the primary cause of mortality [134,135]. For 9 years snags were studied in Modoc and Lassen National Forests, Lassen Volcanic National Park, and Blacks Mountain Experimental Forest. The Jeffrey pine snag creation rate ranged from 17 to 216 new snags/year. Most Jeffrey pine snags (96%) did not decrease in height over the study period. The average annual fall rate was 6.8% for Jeffrey pine snags. Small-diameter snags were more likely to fall than larger snags, and Jeffrey pine trees were more likely to fall than break. A prescribed fire on 1 site increased the Jeffrey pine snag fall rate [80].

In Jeffrey pine-mixed-conifer forests of the Sierra San Pedro Mártir, 52.6% and 23% of snags were Jeffrey pine and white fir, respectively. Snag DBH averaged 22.8 inches (57.9 cm) for all species and ranged from 1 to 43.8 inches (2.6-111.3 cm). Snag height averaged 43 feet (13 m) and ranged from 6.2 to 95.5 feet (1.9-29.1 m). A majority (85%) of snags were large (>12 inch (30 cm) DBH). Snag density averaged 3.95/ha, but snag distribution was patchy. Thirty-five percent of plots had no snags, 65% had less than the average density, and 18% had over 10 snags/ha. Snag abundance increased following severe drought conditions between 1999 and 2003. The highly variable snag attributes caused researchers to question management guidelines with uniform snag targets [162]. For additional information on decomposition and nutrient cycling in Jeffrey pine forests, see the in-depth study of burned and unburned Jeffrey pine forests in Little Valley, Nevada, by Stark [160].

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