Pinus contorta Dougl. ex. Loud.

Lodgepole Pine

Pinaceae -- Pine family

James E. Lotan and William B. Critchfield

Lodgepole pine (Pinus contorta) is a two-needled pine of the subgenus Pinus. The species has been divided geographically into four varieties: P. contorta var. contorta, the coastal form known as shore pine, coast pine, or beach pine; P. contorta var. bolanderi, a Mendocino County White Plains form in California called Bolander pine; P. contorta var. murrayana in the Sierra Nevada, called Sierra lodgepole pine or tamarack pine; and P. contorta var. latifolia, the inland form often referred to as Rocky Mountain lodgepole pine or black pine. Although the coastal form grows mainly between sea level and 610 m (2,000 ft), the inland form is found from 490 to 3660 m (1,600 to 12,000 ft).

Habitat

Native Range

Lodgepole pine is an ubiquitous species with a wide ecological amplitude. It grows throughout the Rocky Mountain and Pacific coast regions, extending north to about latitude 64° N. in the Yukon Territory and south to about latitude 31° N. in Baja California, and west to east from the Pacific Ocean to the Black Hills of South Dakota. Forests dominated by lodgepole pine cover some 6 million ha (15 million acres) in the Western United States and some 20 million ha (50 million acres) in Canada.

{The native range of Pinus contorta}
- The native range of lodgepole pine.

Climate

Lodgepole pine grows under a wide variety of climatic conditions (52). Temperature regimes vary greatly. Minimum temperatures range from 7° C (45° F) on the coast to -57° C (-70° F) in the Northern Rocky Mountains. Maximum temperatures range from 27° C (80° F) along the coast and at high elevations to well over 38° C (100° F) at low elevations in the interior. Average July minimums frequently are below freezing at high elevations. Lodgepole seedlings are relatively resistant to frost injury in some locations (16,42) and often survive in "frost-pockets" where other species do not.

At low elevations in the interior, lodgepole pine grows in areas receiving only 250 mm (10 in) of mean annual precipitation, whereas it receives more than 500 mm (200 in) along the northern coast. Many interior sites often are low in summer rainfall. Seasonal distribution of precipitation is significant; snowfall supplies most of the soil water used for rapid growth in early summer. Temperatures are frequently favorable for germination after snowmelt, and germination occurs rapidly. Lodgepole is very intolerant of shade and generally grows best in full sunlight.

Soils and Topography

Lodgepole pine grows on soils that vary widely but are usually moist. Growth is best where soil parent materials are granites, shales, and coarse-grained lavas (24,27); other soils have developed from glacial till of widely varying composition, Recent, Tertiary, and Oligocene alluvium and colluvium (from such sources as quartzites and argillites), limestone of the Belt geologic series, pumice, and volcanic ash. Lodgepole pine is seldom found on the generally drier soils derived from limestone. In Canada, however, extensive stands occur on calcareous glacial tills (56). Glacial drift provides a balance of moisture and porosity on which the species seems to thrive, as in Alberta, where it grows better on glacial tills than on alluvial soils or lacustrine deposits. In Montana, highly calcareous soils derived from dolomitic limestone usually do not support lodgepole pine, subalpine fir (Abies lasiocarpa), and Engelmann spruce (Picea engelmannii), although they do support Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca). Nevertheless, soils developed in colluvium from other types of limestone and calcareous glacial till do support stands of lodgepole pine.

Extensive stands of lodgepole pine (var. latifolia) occur on soils classified as Inceptisols or Alfisols in the interior forests. Although the species commonly grows on Andepts and does well on these soils in some areas, the Boralfs and Ochrepts probably support better tree development and more extensive stands. Frequently lodgepole pine soils on Boralfs and Ochrepts have cryic soil temperature regimes. In the Blue Mountains of Oregon lodgepole pine does well on Andepts, where it is nearly always found on volcanic ash or alluvial material overlying residual basaltic soils, at elevations between 910 and 2130 m (3,000 and 7,000 ft). The ash cap soils are deeper and hold more moisture than the residual soils.

The coastal form of lodgepole pine (var. contorta) is often found on Histosols (peat bogs or muskegs) in southeastern Alaska, British Columbia, and western Washington, and on dry, sandy, or gravelly sites farther south along the coast on Inceptisols, Alfisols, and Ultisols.

Soil properties and soil moisture often favor lodgepole pine locally over other species. Lodgepole pine grows on wet flats and poorly drained soils in the Cascade Range in Washington and Oregon, and the Sierra Nevada in California. Soils with underlying hardpan support lodgepole pine to the exclusion of such species as ponderosa pine (Pinus ponderosa), redwood (Sequoia sempervirens), or Douglas-fir in the Sierra Nevada, eastern Oregon, and Mendocino County, CA. Lodgepole pine also grows on level sites with and without high water tables in central Oregon where frost tolerance during germination allows its establishment to the exclusion of other species. Extensive stands are found in these areas on well drained sites above 1600 m (5,250 ft), with patterns of occurrence attributed to past fires.

On infertile soils, lodgepole pine is often the only tree species that will grow. Nevertheless, experiments have demonstrated significant growth increase from fertilization, particularly nitrogen (15).

Lodgepole pine thrives in a wide variety of topographic situations. It grows well on gentle slopes and in basins, but good stands are also found on rough and rocky terrain and on steep slopes and ridges, including bare gravel. Northern and eastern slopes are more favorable than southern and western aspects (3).

Associated Forest Cover

Lodgepole pine grows both in extensive, pure stands, and in association with many western conifers. The forest cover type Lodgepole Pine (Society of American Foresters Type 218) (26) exists as a pure (80 percent or more) component of basal area stocking, as a majority (50 percent or more), or as a plurality (20 percent or more). The cover type includes all recognized subspecies of Pinus contorta.

Lodgepole pine is a component in 27 of the 55 SAF western forest cover types. In the Northern Interior (Boreal) group it is represented in White Spruce (Type 201), White Spruce-Aspen (Type 251), White Spruce-Paper Birch (Type 202), Paper Birch (Type 252), and Black Spruce (Type 204).

It is a component in all six high elevation cover types: Mountain Hemlock (Type 205), Engelmann Spruce-Subalpine Fir (Type 206), Red Fir (Type 207), Whitebark Pine (Type 208), Bristlecone Pine (Type 209), and California Mixed Subalpine (Type 256). At middle elevations in the interior it is a minor component of seven other types: Interior Douglas-Fir (Type 210), Western Larch (Type 212), Grand Fir (Type 213), Western White Pine (Type 215), Blue Spruce (Type 216), Aspen (Type 217), and Limber Pine (Type 219). In the North Pacific forests, it is a component in Coastal True Fir (Type 226), Western Redcedar-Western Hemlock (Type 227), Western Redcedar (Type 228), Douglas-Fir-Western Hemlock (Type 230), Port-Orford-Cedar (Type 231), and Redwood (Type 232). At low elevations in the interior it is associated with Interior Ponderosa Pine (Type 237) and in the South Pacific forests it is a component of Jeffrey Pine (Type 247).

Lodgepole pine, with probably the widest range of environmental tolerance of any conifer in North America, grows in association with many plant species (30,50,59,60). The lodgepole pine forest type is the third most extensive commercial forest type in the Rocky Mountains.

Lodgepole pine's successional role depends upon environmental conditions and extent of competition from associated species. Lodgepole pine is a minor seral species in warm, moist habitats and a dominant seral species in cool dry habitats. It is often persistent even on cool and dry sites and can attain edaphic climax at relatively high elevations on poor sites. Fire regimes have played a role in this successional continuum, especially where repeated fires have eliminated a seed source for other species (27). Lodgepole pine may even overwhelm a site with seed stored in serotinous cones. It has four basic successional roles (50):

Minor Seral- A component of even-aged stands rapidly being replaced by shade-tolerant associates in 50 to 200 years.

Dominant Seral- The dominant cover type of even-aged stands with a vigorous understory of shade-tolerant species that will replace lodgepole pine in 100 to    200 years.

Persistent- The dominant cover type of even-aged stands with little evidence of replacement by shade-tolerant species.

Climax- The only tree species capable of growing in a particular environment; lodgepole pine is self-perpetuating.

Life History

The following statements apply principally to lodgepole pine in the most important part of its range; namely northern Colorado, Wyoming, Montana, northern Utah, Idaho, eastern Oregon, western Alberta, and southern British Columbia.

Reproduction and Early Growth

Flowering and Fruiting- Male and female strobili generally are home separately on the same tree in this monoecious species, with female flowers most often at the apical end of main branches in the upper crown, and male flowers on older lateral branches of the lower crown. The reddish purple female flowers grow in whorls of two to five and are 10 to 12 mm (0.4 to 0.5 in) long. The pale yellow to yellowish orange male flowers are crowded clusters of catkins at the base of new shoots and are 8 to 14 mm (0.3 to 0.6 in) long. It is not uncommon to find a dominance of maleness or femaleness on individual trees.

Pollen generally matures in mid-May to mid-July (table 1) (20,52). The time at which pollen matures appears to be related to elevation and climate.

Table 1- Time of pollen shedding in natural stands of lodgepole pine (20,52, modified)


Stand location

Elevation¹
Years observed Date of peak shedding

m ft
Vancouver, BC - - 2 Middle to late May
Northwestern Washington 150 500 10 May 12
Mendocino White Plains, California - - 1 June 9
Northern Cascades 1200 4,000 - Mid-June
Northern Idaho; western Montana - - 10 June 13
Central and eastern Washington and Oregon 790 to 1300 2,600 to 4,250 - June 13
Southeastern Alberta (subalpine forest) - - 10 June 22
Sierra Nevada, California 1820 6,000 3 June 22
Central Montana; Yellowstone region - - 10 June 25
Northern Utah 2190 7,200 2 July 12
Southern Idaho 2070 6,800 1 July 7
Northern Idaho; western Montana 670 to 1265 2,200 to 4,150 10 June 6
Eastside Montana; Yellowstone National Park 975 to 2060 3,200 to 6,750 10 June 17

¹Dash indicates data are not available.

Seed cones usually mature in August, September, or October, more than a year after pollination. Inland forms and high elevation stands apparently mature earlier than coastal forms or low elevation stands. Cones open in early September in the Northern Rocky Mountains. Cone maturity is indicated by a change in color from purple-green to light brown (54).

Seed Production and Dissemination- Lodgepole pine produces viable seed at an early age, commonly 5 to 10 years; germination percentage is as high as that of seed borne by mature trees. Pollen flowers have been observed on 2-0 seedlings in the Lucky Peak Nursery near Boise, ID.

Lodgepole pine is a prolific seed producer. Good crops can be expected at 1- to 3-year intervals, with light crops intervening. The cones withstand below freezing temperatures and are not generally affected by cone- and seed-feeding insects. Only squirrels and coreid bugs are significant seed predators. Seed production should not be taken for granted, however. Complete seed crop failures have occurred at 2800 m (9,200 ft) in northwest Wyoming for 2 to 4 years in a row (42).

Cone production of individual dominant and codominant trees can vary from a few hundred to a few thousand per tree (37). Cones are persistent, and serotinous (closed) cones accumulate for decades. Annual production may run from 173,000 to 790,000 seeds per hectare (70,000 to 320,000/acre) with half to one-third available for annual seedfall (27). An annual seedfall of 99,000 to 222,000 seeds per hectare (40,000 to 90,000/acre) was found in central Montana (58). These figures might be considered typical for interior lodgepole pine where some portion of the trees are of the serotinous type. In Oregon, where the nonserotinous cone habit is prevalent, seedfall ranged from about 35,000 to over 1.2 million/ha (14,000 to 500,000/acre) (21). Most years seedfall was on the order of hundreds of thousands per hectare. Where stored seeds are in the millions per hectare (in closed cones), the number of seeds stored is probably 10 times that of seeds produced annually (37).

Although the number of fully developed seeds per cone varies from as few as 1 to 2 to as many as 50, a normal average for large cone lots in the Rocky Mountains is from 10 to 24 seeds per cone (42). Sierra Nevada populations range from 5 to 37 seeds per cone (20).

The serotinous cone habit varies over wide geographic areas as well as locally (37). Serotinous cones are not common in eastern Oregon, rare in coastal populations, and absent in the Sierra Nevada and southern California and Baja California populations (20). Although common in the Rocky Mountains, this cone habit varies considerably (37). Many stands in the Rockies have less than 50 percent serotinous-cone trees.

Lodgepole pine has long been regarded as a fire-maintained subclimax type. Its ability to regenerate in extremely dense stands to the exclusion of other species can be attributed to the closed cone habit. Millions of seeds per hectare are held in reserve for many years and are readily available to germinate on the seedbed prepared by fire. Recent evidence seems to indicate that fire selects strongly for the closed cone habit (49).

Serotinous cones do not open at maturity because of a resinous bond between the cone scales. The bonds break with temperatures between 45° and 60° C (113° to 140° F) (48), and cone scales are then free to open hygroscopically. Large quantities of seeds are thus available for regenerating a stand following fire. Closed cones at or near the soil surface (less than 30 cm or about 12 in) are also subjected to temperatures from insolation sufficient to open them and may provide seed in harvested areas. Some seeds may be damaged by fire, however, particularly in fires burning in logging slash.

Seeds stored in serotinous cones on the tree remain viable for years. Apparently, prolonged viability can be maintained so long as cones or seeds are not in contact with the ground. Once cones are on the ground, cones open. Damping-off fungi may infect the seed, rodents may feed on the seeds, or germination may occur; for the most part, seeds are not stored in the soil.

Lodgepole pine has relatively small seeds for pine. Seed weights vary considerably, ranging from 2.3 mg (0.04 grains) per seed in the Interior of Canada to 11.4 mg (0.18 grains) per seed in the Sierra Nevada (20). Lodgepole pine seeds average about 298,000 cleaned seeds per kilogram (135,000/lb) for varieties contorta, 258,000/kg (117,000/lb) for murrayana, and 207,000/kg (94,000/lb) for latifolia (54). Density of seedfall 20 m (66 ft) from the timber edge is only 10 to 30 percent of that at the timber edge for stands in the Rocky Mountains (fig. 1) (42). Dispersal of sufficient seed to adequately restock an area often is only about 60 m (200 ft) (23,38). Prevailing winds, thermal effects, or scudding on the snow may disperse seeds far beyond these distances, however.

{P. contorta: sound seed per hectare}
Figure 1- Sound seed per hectare as a function of distance
from the nearest timber edge.

The annual seedfall from nonserotinous cones helps in restocking relatively minor disturbances in the stand, in maintaining the presence of lodgepole pine in mixed stands, and in expanding conifers into other vegetative types. Seldom do we find stands without some trees of the open-coned type. The efficacy of this seed source can be seen in the dense stands of lodgepole pine along road cuts, powerline rights-of-way, and ditches or where disturbance occurs near lodgepole pine stands.

Studies of seedfall have shown variation in the number of seeds released soon after cone maturation, but most seeds (80 to 90 percent) are released before the following growing season (27).

Where large amounts of seed are stored in serotinous cones, a most effective means of seed dispersal in clearcuts is from cones attached to the slash and those knocked from the slash and scattered over the forest floor during slash disposal. Many cones on or near the ground are opened by normal summer soil surface temperatures (35). In Montana 83 percent of the cones on the ground opened the first year on south slopes compared to 40 percent on north slopes. Maximum seed release from serotinous cones near the ground takes place during the first year of exposure. In fact, cones may open after the first few minutes of exposure to temperatures high enough to break the resinous bonds.

In slash, serotinous cones that are well above the ground behave like those on a tree- they remain closed, and stored seeds remain viable for years.

Seeds in unopened cones and those released from the slash may also be lost to rodents, fungi, and other destructive agents. Seeds from closed cones are usually available only for the first growing season following harvest, but stocking from open-cone seed sources can continue to increase for several years.

Slash disposal on areas where regeneration is planned from serotinous cones must be carefully planned and executed. Seed supply will be largely destroyed if slash to be burned is piled before cones have had a chance to open (38). Piling slash should be delayed until sufficient cones have opened to assure adequate stocking. Piling then scatters seeds and opened cones and helps prepare the seedbed. Piling slash after germination can also decrease stocking because young seedlings are trampled or buried.

Broadcast burning may hasten release of seeds from cones not in a position to open from high soil-surface temperatures. Some seeds will be destroyed, however; the amount will vary with fire intensity.

Seedling Development- Germination under field conditions is good if climate and seedbed are favorable. Best germination occurs in full sunlight and on bare mineral soil or disturbed duff, free of competing vegetation. Germination is epigeal. Temperatures fluctuating between 8° and 26° C (47° and 78° F) favor germination. Adequate soil moisture is required for germination and survival during the critical few weeks following germination (34,51,55). In southwest Montana and southeast Idaho, 75 to 90 percent of a season's total germination occurred during the 2 weeks following snowmelt in late June (34), when the soil was saturated and temperatures were favorable. Germination can be delayed if cones do not open during the previous summer.

Although lodgepole pine germinates well on most organic seedbeds, such materials tend to dry faster than mineral soil and seedlings often die in this seedbed. Lodgepole pine seeds have little need for stratification and germination depends largely upon temperature (20). At optimum temperatures and moisture, almost 100 percent of the seeds germinate rapidly.

Both shading and competition inhibit germination and survival. Newly germinated seedlings are relatively insensitive to temperature extremes. Because residual overstory following partial cutting usually does not provide the most favorable conditions for regeneration, clearcutting is generally recommended. On some areas, however, lodgepole pine has established itself in the shade of lightly cut or uneven-aged stands and may persist for many years in the understory. Some of these trees eventually may establish a crown sufficient to permit reasonable growth.

Drought is a