Larix occidentalis

Pinaceae -- Pine Family

    Wyman C. Schmidt and Raymond C. Shearer

    Western larch (Larix occidentalis), a deciduous conifer, is also  called tamarack and western tamarack; less commonly used names are  hackmatack, mountain larch, and Montana larch (17). It is largest of the  larches and is the most important timber species of the genus. Western  larch is used for lumber, fine veneer, poles, ties, mine timbers, and  pulpwood.

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This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):

BLM PHYSIOGRAPHIC REGIONS [22]:

2 Cascade Mountains

5 Columbia Plateau

8 Northern Rocky Mountains

9 Middle Rocky Mountains

16 Upper Missouri Basin and Broken Lands

IDMTORUTWAWY

ABBC

Western larch occurs from southeastern British Columbia and extreme western Alberta southward into eastern Washington, western Montana, northern Oregon, and northern and west-central Idaho [40,46,72,115]. It has been established in a planting in Salt Lake County, Utah [157], and one source reports that its range extends into Colorado [70].

Western larch grows in the Upper Columbia River Basin of northwestern  Montana, northern and west central Idaho, northeastern Washington, and  southeastern British Columbia; along the east slopes of the Cascade  Mountains in Washington and north-central Oregon; and in the Blue and  Wallowa Mountains of southeastern Washington and northeastern Oregon.

     
- The native range of western larch.

Larix occidentalis Nutt.:
Canada (North America)
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Trees to 50m; trunk to 2m diam., usually (when forest grown) branch-free over most of height; crown short, conic. Bark reddish brown, scaly, with deep furrows between flat, flaky, cinnamon-colored plates. Branches horizontal, occasionally drooping in lower crown of open-grown trees; twigs orange-brown, initially pubescent, becoming glabrous or very sparsely pubescent during first year. Buds dark brown, generally puberulent, scale margins erose. Leaves of short shoots 2--5cm × 0.65--0.80mm, 0.4--0.6mm thick, keeled abaxially, with shallow convex midrib adaxially, pale green; resin canals 20--50 µm from margins, each surrounded by 5--7 epithelial cells. Seed cones 2--3 × 1.3--1.6cm, on curved stalks 2.5--4.5 ´ 3.5--5mm; scales 45--55, margins entire, adaxial surface pubescent; bracts tipped by awn to 3mm, exceeding scales by ca. 4mm. Pollen 71--84µm diam. Seeds reddish brown, body 3mm, wing 6mm. 2 n =24.

More info for the terms: basal area, density

Western larch is a fast growing, long-lived, deciduous conifer native to alpine and subalpine forests of the northwestern United States and adjacent Canada [4,45,115,154]. Trees over 900 years old have been reported [80,115,116].

One of the world's largest larches, western larch typically grows 100 to 180 feet tall (30-55 m) but can be over 200 feet (60 m) tall [50,57,71,72,115,157], with diameters up to 6 feet (2 m) [50,62,72,157]. Basal area increases rapidly to about age 40, then decelerates and nearly levels off after age 100 [115]. A deep, spreading root system stabilizes these large trees [57,72]. In a synthesis of literature on northwestern trees, Minore [93] ranked western larch root depth in the middle category of 5 categories.

Bark in mature trees is thick and furrowed into large, flaky plates [50,71,115,157]. At age 50, basal bark thickness ranges from 5 to 10 inches (12-25 cm), and at age 100 bark is 10 to 18 inches (25-45 cm) thick [12]. Western larch trunks are usually bare for a half to a third of the height when in stands, while trees in the open may have branches to within a few feet of the ground [71,72,157]. Crowns are generally short, open, and pyramidal with nearly horizontal branches, though branches may droop in the lower crown of older trees grown in the open [50,57,71,72]. Crown length, width, and density were all ranked low in Minore's [93] synthesis of literature on northwestern trees.

Branches are stout and brittle, changing from pubescent to glabrous with age. Buds are small, rounded, and hairless [71,72,157]. As trees mature, clustered epicormic branches replace older branches, beginning with the lower portion of the crown. Eventually, epicormics, which grow from dormant buds at the base of first order branches, comprise the entire crown [83].

Clusters of 15 to 30 slender, soft, spirally-arranged needles 1 to 2 inches (2.5-5.0 cm) long arise from dwarf twigs [71,72,157]. Western larch foliage is replaced annually [55,57].

Male western larch cones are 0.4 inch (1 cm) long [71,157]. Ovulate cones are papery, 1 to 1.5 inches long (2.5-3.5 cm) and 0.5 to 0.6 inch (1.3-1.6 cm) wide with long subtending bracts [12,50,71,72,157]. Seeds are 0.1 inch (3 mm) long with 0.2 inch (6 mm) wings [50,71,72,157].

The preceding description provides characteristics of western larch relevant to fire ecology and is not meant to be used for identification. Keys for identifying western larch are available [40,70,82].

Tree, Deciduous, Monoecious, Habit erect, Trees without or rarely having knees, Tree with bark rough or scaly, Young shoots 3-dimensional, Buds not resinous, Leaves needle-like, Leaves alternate, Needle-like leaf margins entire (use magnification), Leaf apex acute, Leaves < 5 cm long, Leaves < 10 cm long, Leaves not blue-green, Needle-like leaves flat, Needle-like leaves not twisted, Needle-like leaf habit erect, Needle-like leaf habit drooping, Needle-like leaves per fascicle mostly 1, Needle-like leaves per fascicle > 10, Needle-like leaf sheath early deciduous, Needle-like leaf sheath persistent, Twigs pubescent, Twigs not viscid, Twigs with peg-like projections or large fascicles after needles fall, Berry-like cones orange, Woody seed cones < 5 cm long, Bracts of seed cone included, Seeds red, Seeds brown, Seeds winged, Seeds unequally winged, Seed wings prominent, Seed wings equal to or broader than body.

More info for the terms: resistance, tree

Western larch occurs in mountain valleys and lower slopes, often in somewhat swampy areas [50,71]. It needs well-lighted areas for maximum development, so it performs best in open stands [72]. Western larch is usually found at elevations of 1,500 to 5,500 feet (460-1,700 m) in the northern portions of its range and may be found at elevations over 7,000 feet (2,100 m) in the southern parts of its distribution [50,72,117]. Latitude and elevation affected genetic variation patterns of western larch populations in the Rocky Mountains. Populations from more northern areas and from high elevations had lower growth potential, lower resistance to disease, and lower survival [108]. Elevational ranges for some states and 1 province in western larch's range are:

Montana 3,000-7,200 feet (900-2200 m) [12,79] Oregon 3,500-6,500 feet (1000-2000 m) Washington 2,000-5,500 feet (600-1700 m) [79] British Columbia 2,000-5,550 feet (600-1700 m) [12]

Climate: Western larch occupies relatively cool, moist climatic zones. Its upper elevational range is limited by low temperatures, while the lower extreme is limited by low precipitation [45,46,115,117].

Average climatic conditions for western larch's range are [115]:

Temperature 45° Fahrenheit (7° C) Maximum temperature 84° Fahrenheit (29° C) Minimum temperature 15° Fahrenheit (-9° C) Growing season temperature 60° Fahrenheit (16° C) Frost free days 60-160 days Annual precipitation 28 inches (710 mm) Growing season precipitation 6 inches (160 mm) Snowfall 103 inches (2620 mm)

Climatic conditions for 4 forest habitat types where western larch occurs are [45]:

Douglas-fir grand fir western redcedar-
western hemlock Engelmann spruce-
subalpine fir Mean annual precipitation (mm) 370-570 500-680 570-1,130 700-850 Mean growing season precipitation (mm) 180-270 200-290 210-370 200-320 Mean annual snowfall (cm) 120-350 193-450 130-560 200-620 Mean annual temperature (°C) 4.0-7.5 2.5-4.0 2.5-7.8 1.0-2.5 Frost-free conditions (days/year) 40-140 35-80 50-170 40-70

Soil: Western larch is found on a wide variety of soil types, most of which are derived from bedrock or glacial till, but some are of  loessial or volcanic ash origin. Deep, porous soils, such as those of mountain slopes and valleys are ideal, and growth is related to soil depth [46,72,115,116,117]. Western larch is also quite dependent on mineral soil or burned seedbeds, more so than any associated tree species including lodgepole pine [46,115]. Western larch is adapted to medium and coarse textured soils with a pH of 6 to 7, and has no salinity tolerance [154].

Topography: Western larch occupies valley bottoms, benches, and mountain slopes. It is found on all exposures but is more common on north and east aspects. South and west exposures are often too severe for seedling establishment [115,116]. This trend is more pronounced in the southern parts of its range, where it is found almost exclusively on north- and east-facing slopes [45,46].

Harsh environments: Western larch has moderate to high resistance to wind throw because its root system provides good anchorage. It is adapted to a wide range of temperatures, but since buds open earlier than associated conifers, hard frosts in late spring may result in cone crop loss [117]. Frozen seed cones are associated with nighttime air temperatures of 25° Fahrenheit (-4° C) or less [27,130]. Snow and ice are generally not threats to western larch survival. Wet snow when needles are present (early spring or late fall) may cause snow bend, but rarely results in permanent damage [117].

More info for the terms: climax, tree

Except when it is young, western larch is rarely found in pure stands. Its most
common tree associate is Douglas-fir (Pseudotsuga menziesii), and on
low-elevation dry sites it is found with ponderosa pine (Pinus ponderosa).
Common associates in warm, moist forests include grand fir (Abies
grandis), western hemlock (Tsuga heterophylla), western redcedar
(Thuja plicata), and western white pine (P. monticola). In cool,
moist, subalpine forest types Engelmann spruce (Picea engelmannii),
subalpine fir (A. lasiocarpa), lodgepole pine (Pinus contorta), and mountain
hemlock (Tsuga mertensiana) are more common.

Hardwoods that occur with western larch include paper birch (Betula papyrifera),
black cottonwood (Populus balsamifera ssp. trichocarpa), and quaking aspen
(P. tremuloides) [72,115,116,126,132].

Major understory associates include common beargrass (Xerophyllum tenax), huckleberry
(Vaccinium spp.), thimbleberry (Rubus parviflorus), menziesia (Menziesia ferruginea),
ninebark (Physocarpus malvaceus), serviceberry (Amelanchier spp.),
Oregon boxwood (Paxistima myrsinites), and bearberry (Arctostaphylos uva-ursi).

Western larch is not considered a climax species, but it is a
long-lived early successional species. Refer to Successional Status
for more details [34,53,88,116,156]. Classifications describing
plant communities in which western larch is an important seral species include the following:

Idaho: [33,34,64,144]

Montana: [65,66,106]

Oregon: [51,63]

Washington: [34,51,63]

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This species is known to occur in association with the following Rangeland Cover Types (as classified by the Society for Range Management, SRM):

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SRM (RANGELAND) COVER TYPES [134]:

409 Tall forb

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This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):

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SAF COVER TYPES [42]:

205 Mountain hemlock

206 Engelmann spruce-subalpine fir

210 Interior Douglas-fir

212 Western larch

213 Grand fir

215 Western white pine

218 Lodgepole pine

220 Rocky Mountain juniper

224 Western hemlock

226 Coastal true fir-hemlock

227 Western redcedar-western hemlock

228 Western redcedar

233 Oregon white oak

237 Interior ponderosa pine

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This species is known to occur in association with the following plant community types (as classified by Küchler 1964):

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KUCHLER [81] PLANT ASSOCIATIONS:

K004 Fir-hemlock forest

K010 Ponderosa shrub forest

K011 Western ponderosa forest

K012 Douglas-fir forest

K013 Cedar-hemlock-pine forest

K014 Grand fir-Douglas-fir forest

K015 Western spruce-fir forest

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This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):

ECOSYSTEMS [53]:

FRES20 Douglas-fir

FRES21 Ponderosa pine

FRES22 Western white pine

FRES23 Fir-spruce

FRES24 Hemlock-Sitka spruce

FRES25 Larch

FRES26 Lodgepole pine

Western larch grows on a wide variety of soils. The most extensive soils  have developed in glacial till or colluvium composed of materials derived  from limestone, argillite, and quartzite bedrocks of the Precambrian belt  geologic series. Larch also grows on soils developed in Recent and  Tertiary alluvium and Pleistocene lake sediments. Most soils suitable for  the growth of western larch are deep and well drained. Soils developed in  glacial till, colluvium, and recent alluvium have nongravelly to gravelly  loamy surfaces and gravelly to extremely gravelly loamy subsoils. Volcanic  ash is often incorporated into the surface horizon. Soils developed in  Tertiary sediments or Pleistocene lake sediments have silt loam surfaces  and silt loam, silty clay loam, silty clay, or clay subsoils.

    Most soils supporting the growth of western larch are classified in two  orders of the soil taxonomy: Inceptisols and Alfisols. Occasionally  western larch is found on soils of the order Spodosols, but Spodosols are  not extensive within the range of western larch and generally occur above  the upper elevational limits of the species. A majority of the soils  supporting the growth of western larch are the Cryoboralf, Cryochrept, and  Cryandept great groups. Mean annual soil temperature of the soils within  the great groups is about 5° C (41° F) at 51 cm (20 in). At low  elevations on southern or western exposures within the range of western  larch, soil temperatures are warmer and soils supporting the growth of  western larch are in the Eutroboralf and Eutrochrept great soil groups.

    Western larch grows best on the more moist Eutrochrepts or Eutroboralfs  and the lower elevation (warmer) Cryochrepts and Cryoboralfs. It is  commonly found growing on valley bottoms, benches, and north- and  east-facing mountain slopes. South and west exposures are often too severe  for larch seedling establishment, particularly on the drier sites found at  larch's lower elevational limits and the southern portion of its range. On  moist sites found in the mid-to northern-portion of its range and on mid-  to high-elevation sites, larch grows on all exposures.

Western larch grows in a relatively moist-cool climatic zone, with low  temperature limiting its upper elevational range and deficient moistures  its lower extremes (44). Mean annual temperature within the larch zone is  about 7° C (45° F), but annual maximums average 29° C (84°  F) and minimums average -9° C (15° F) (table 1) (35). Average  temperatures during the May through August growing season are about 16°  C (60° F) with July the warmest month. The frost-free season varies  from about 60 to 160 days, usually from early June through early  September. Frosts can occur any month of the year.

    Table 1- Summary of weather data from within the range  of western larch¹            °C  °F      Average Temperature             Annual maximum  29    84         Annual minimum   -9    15         Annual mean    7    45         Annual absolute maximum  41  106         Annual absolute minimum  -37    -34         Growing season only  15    59        mm  in      Average precipitation             Total annual    710    28         Total during growing season²    160      6         Total snowfall  2620  103      ¹Data compiled  from 12 weather stations in Idaho, 10 in Montana, 3 in Oregon, and 4 in  Washington using U.S. Department of Commerce summaries for 1951 through  1960 (35). 
²May through August.        Annual precipitation in larch forests averages about 710 mm (28 in) in  the north part of its range to 810 mm (32 in) in the south. The extremes  where larch grows are about 460 mm (18 in) and 1270 mm (50 in). About  one-fifth of the annual precipitation occurs during the May through August  growing season, most of it in May and June. July and August are usually  dry and are characterized by clear, sunny days (60 to 80 percent of the  daylight hours), low humidity, and high evaporation rates (44). Elevation  and geographic location affect both the amount and the form of  precipitation. On midelevation sites, snow commonly blankets most larch  forests from November to late April and accounts for over half the total  precipitation. Snow accounts for an even higher proportion of the total  precipitation in the northerly higher elevation Portions of larch forests.  One high elevation larch site at Roland, ID, receives an average of 620 cm  (244 in) of snow annually. Lower elevation sites commonly receive an  average of more than 150 cm (60 in) of snow.

Mountain valleys and lower slopes; 500--1600m; B.C.; Idaho, Mont., Oreg., Wash.

Systems

• Terrestrial

Western larch is a long-lived seral species that always grows with other  tree species. Young stands sometimes appear to be pure, but other species  are in the understory, Douglas-fir (Pseudotsuga menziesii var.  glauca) is its most common tree associate. Other common tree  associates include: ponderosa pine (Pinus ponderosa) on the lower,  drier sites; grand fir (Abies grandis), western hemlock (Tsuga  heterophylla), western redcedar (Thuja plicata), and western  white pine (Pinus monticola) on moist sites; and Engelmann spruce  (Picea engelmannii), subalpine fir (Abies lasiocarpa), lodgepole  pine (Pinus contorta), and mountain hemlock (Tsuga  mertensiana) in the cool-moist subalpine forests (44).

    Western larch makes up a majority or plurality in the forest cover type  Western Larch (Society of American Foresters Type 212) (43). It is  included in 11 other cover types:

    205 Mountain Hemlock 
206 Engelmann Spruce-Subalpine Fir 
210 Interior Douglas-Fir 
213 Grand Fir 
215 Western White Pine 
218 Lodgepole Pine 
220 Rocky Mountain Juniper 
224 Western Hemlock 
227 Western Redcedar-Western Hemlock 
228 Western Redcedar 
237 Interior Ponderosa Pine

    Classification systems based on potential natural vegetation have been  developed for much of the geographic area where western larch grows. Larch  is a seral species in 13 of the 21 habitat types described for eastern  Washington and northern Idaho (7). In Montana, larch is a significant  component in 20 of the 64 forest habitat types (21). Of these 20 habitat  types, larch is a major seral species in 12, and a minor seral species in  8. These habitat types are found within the following forest series: the  relatively dry-warm Douglas-fir; the moist grand fir, western redcedar,  and western hemlock; and the cold-moist subalpine fir.

    Larch forests typically have a rich understory flora with dense  herbaceous and less dense shrub layers. It is not unusual to find as many  as 7 tree species and 40 undergrowth species in plots of 405 m²  (4,356 ft²) (21). On a 40-ha (100-acre) study area on the Coram  Experimental Forest in northwestern Montana, 10 conifer, 21 shrub, and 58  herbaceous species were recorded (31). Some of the common understory  species associated with larch are the following:

    Shrubs

      Rocky Mountain maple  Acer glabrum      Sitka alder  Alnus sinuata      Serviceberry   Amelanchier alnifolia      Oregongrape  Berberis repens      Menziesia  Menziesia ferruginea      Mountain lover  Pachistima myrsinites      Ninebark  Physocarpus malvaceus      Rose  Rosa spp.      Thimbleberry  Rubus parviflorus      Common snowberry  Symphoricarpos albus      Dwarf huckleberry  Vaccinium caespitosum      Blue huckleberry  Vaccinium globulare      Scouler willow  Salix scouleriana      Spiraea  Spiraea betulifolia        Herbs

      Wild sarsaparilla  Aralia nudicaulis      Kinnikinnick  Arctostaphylos uva-ursi       Arnica  Arnica latifolia      Pinegrass  Calamagrostis rubescens      Queenscup  Clintonia uniflora      Fireweed  Epilobium angustifolium      Twinflower  Linnaea borealis      Beargrass  Xerophyllum tenax

Mature larches are the most fire-resistant  trees in the Northern Rockies because of their thick bark, their high and  open branching habit, and the low flammability of their foliage. Poles are  moderately resistant, but seedlings and saplings have very little  resistance to fire (44).

    Larch is moderately to highly resistant to windthrow because of its  extensive root system. Isolated old-growth seed trees or those along  cutting boundaries, however, are susceptible to windthrow, particularly  those on upper slopes and ridgetops, or those in narrow canyons and  saddles where winds are channeled (35).

    Because larch is deciduous, its branches seldom accumulate excessive  amounts of either snow or ice. Early fall or late spring snows  occasionally catch larch with a full complement of needles and cause  severe bending. After a heavy June snow on the Coram. Experimental Forest,  young larch were completely flattened, but they recovered surprisingly  well with little apparent long-term damage (34).

    Young larch is extremely sensitive to noxious fumes, but because it is  deciduous, the tree accumulates fewer harmful deposits than other  conifers. Fluorine and sulfur dioxide are both harmful, but fluorine is  the more toxic. Fluorides at levels of 30 to 35 p/m produce toxic needle  effects (5).

    Dwarf mistletoe (Arceuthobium laricis) is the most damaging  disease-causing parasite of larch. It can infect seedlings as young as 3  to 7 years old and continue throughout the life of the tree (49). In  addition to killing tree tops, reducing seed viability, creating  conditions suitable for entry of other diseases and insects, and causing  burls, brashness, and some mortality, it decreases height and diameter  growth. Basal area growth reductions can be expected as follows (22):  light infection, 14 percent; medium infection, 41 percent; and heavy  infection, 69 percent.

    Infected residual-stand overstories left after logging or fires promptly  infect understory stands. Mistletoe seed can be ejected as far as 14 m (45  ft) (42). Thus 50 evenly-spaced, diseased trees per hectare (20/acre) may  infest understory trees with just one crop of mistletoe seeds. Proper  harvest-cutting systems, particularly clearcutting, can substantially  reduce the mistletoe problem.

    Three other important diseases are found in larch: needlecast caused by  Hypodermella laricis, the quinine fungus Fomitopsis  officinalis, and red ring rot caused by Phellinus pini. Many  other less common but potentially dangerous fungi, such as Encoeliopsis  laricina, infect larch but have not caused significant problems in the  past (35).

    Larch casebearer (Coleophora laricella) and western spruce  budworm (Choristoneura occidentalis) are currently the two most  serious insect pests of western larch (35). Casebearer was first detected  in the Northern Rockies in 1957 and since then has spread throughout  virtually the entire larch forest type (11). Introduced and native  parasites, plus adverse weather conditions on many larch sites, appear to  be reducing the casebearer problem, however. Severe defoliation by the  casebearer can substantially reduce tree growth, but mortality usually is  low.

    Western spruce budworm has been a persistent problem wherever heavy  populations of budworm overlap the range of larch (12). The most serious  damage to larch is severance of the terminal leader, which results in an  average loss of about 25 to 30 percent of the height growth for that year  (32).

    Other insect species affecting larch include the larch sawfly (Pristiphora  erichsonii) and the larch bud moth (Zeiraphera improbana) that  cause heavy, but sporadic, damage. The western larch sawfly (Anoplonyx  occidens), the two-lined larch sawfly (Anoplonyx laricivorus),  and the larch looper (Semiothisa sexmaculata incolorata) also  damage larch from time to time. Bark beetles are not generally a serious  problem for larch, but the Douglas-fir beetle (Dendroctonus  pseudotsugae) occasionally attacks weakened trees. At times, the  engraver beetle (Ips plastographus), the larch engraver (Scolytus  laricis), and the false hemlock looper (Nepytia canosaria) damage  larch.

    Damage from larger animals is relatively minor. Rodents, because of  their seed- and seedling-eating habits, can greatly influence seedling  establishment. Larch is apparently unpalatable to most big game species.  In addition, most larch forests occur in areas of heavy snowpack not  suitable for winter game range (35). Bears, however, can be a local  problem. They strip the bark on the lower bole of the most vigorous trees  in young sapling and pole-sized stands during the spring of the year and  often kill the trees.

More info for the terms: competition, duff, flame length, fuel, mesic, natural, succession, tree

Fire is an important management practice for maintaining western larch [10,30,60,91]. Ideally, prescribed burns should expose well-distributed patches of mineral soil and reduce sprouting potential of competitors [67,114,123]. However, even areas with very little burned surface result in significantly better western larch regeneration than unburned sites [10,130]. In good seed crop years, overstocking may result in mesic habitats where too much mineral soil is exposed, and thinning may be necessary to facilitate a vigorous stand [37,67,114,123]. Harsh sites with poor regeneration potential may require planting after burning [10,37].

Norum [67,97] provides detailed recommendations for prescribed burning in western larch-Douglas-fir forests. Based on studies of fire and harvest regimes, Antos and Shearer [2] make recommendations for management practices on grand fir-queencup beadlily habitat type in northwestern Montana.

Timing and Site Conditions: The timing of prescribed burns is important for western larch site preparation; large fuels should be dry and soil moisture low in order to expose mineral soil [10,37,97,99,123]. Norum [98] reported that 10 to 17% water content in small diameter (<4 inch (<10 cm)) fuels is a safe and effective range for burning in western larch-Douglas-fir habitat. Spring and early summer fires usually burn only the surface of the duff layer, while late summer or early fall fires after dry summers tend to be more effective at exposing enough mineral soil for larch regeneration. August or early September, before the fall rains, are the best times for burning north-facing slopes, but on other aspects, there is more flexibility for timing a successful burn [10,37,97,99,123]. Timing of seed dispersal should also be considered when planning fall fires; burning before seedfall is preferable [37]. Depending on site conditions, removing duff from bases of western larch trees to prevent cambium and root damage and/or thinning understory to reduce ladder fuels may be necessary prior to burning [16,67,123].

Fire Intensity: An adequate seedbed for western larch usually results from moderate intensity fires in dry duff. High intensity fires may expose too much mineral soil and result in overstocking [10,37]. Prescribed burning after clearcutting or shelterwood cutting is sometimes used to mimic the effects of severe wildfires on western larch habitat [10,148].

While western larch seedlings usually establish best on severely burned sites [109], underburning may lead to consistent successful natural regeneration but requires careful attention to fuel and site conditions [10,96,104,114]. Harvey and others [69] found burning to remove slash reduced ectomycorrhizal activity after partial cuts in western larch-Douglas-fir forests of northwestern Montana. They recommend against burning to remove slash on harsh sites where understory competition may limit conifer germination or where soil organic matter is low. They suggest underburning is better suited for areas where excessive regeneration is expected or where understory vegetation is desired, especially if burn conditions are chosen to limit duff reduction, which in turn will limit conifer (including western larch) germination.

Models: Reinhardt and Ryan [109,110] present a model for predicting postfire mortality of western larch and 6 other western conifers using bark thickness and percent crown volume. Desired levels of mortality can be predicted using tree species, diameter, height and crown ratio, and maximum allowable flame length. FIRE-BCG simulates fire succession on coniferous forest landscapes of the northern Rocky Mountains, including western larch habitat [78], and FIRESUM models tree establishment, growth, mortality, fuel accumulation, fire behavior, and fuel reduction in ponderosa pine/Douglas-fir forests of the inland northwest [77].

More info for the terms: competition, fire use, mesic, prescribed fire, restoration, succession

Regeneration of western larch after fire depends on site conditions and fire
intensity. After moderate fires in grand fir habitat of the Blue and Wallowa mountains of
northeastern Oregon, western larch in cool, moist areas had increased by the 1st
and the 5th years. After severe fires, the species decreased after the 1st year,
but increased by postfire year 5. In warm, dry
grand fir habitats, moderate fires resulted in a decrease after the 1st year
and no change by the 5th year postfire, while severe fires caused a decrease in
western larch after the 1st year and an increase by 5 years postfire. Western
larch's response to burning in several grand fir associations was [75]:

Plant AssociationFire SeverityWestern larch % coverNotesPrefire1st postfire year 5th postfire year 10th postfire year ----grand fir-beadlily (Clintonia uniflora)severe----25----fire killed all treesgrand fir-twinflower (Linnaea
borealis)moderate1555--------grand fir-grouse huckleberrysevere----0----13 (range 0-30)fire killed all treesgrand fir-grouse huckleberrymoderate----00--------

In early postfire succession in the northern portion of the Bitterroot Mountains,
Montana, western larch formed nearly pure stands on north and east exposures, and
western white pine and Douglas-fir replaced western larch in the absence of fire
in 1929 [85]. Historically, following intense stand-replacing fires in mesic to moist
habitats of the northern Rocky Mountains, even-aged western larch stands often
developed, while in drier habitats, western larch was maintained by frequent surface
fires that minimized competition [1,61].

In ponderosa pine-Douglas-fir forests of the inland northwest, the FIRESUM
model predicts successful regeneration of ponderosa pine with a 10- to 20-year
fire return interval. More severe fires at 50-year intervals predict western
larch dominance for 150 years, then an increase in ponderosa pine, and
Douglas-fir dominance after 200 years. Without fire, Douglas-fir would dominate
the understory and eventually the overstory, limiting regeneration of western
larch and ponderosa pine [77].
For further information on western larch response to fire, see Fire Case Studies.
The Research Project Summary
Vegetation response to restoration treatments in ponderosa pine-Douglas-fir forests of western Montana
provides information on prescribed fire use and postfire response of plant community
species including western larch.

More info for the terms: competition, crown fire, fire suppression, ladder fuels, prescribed burn, shrubs, tree, wildfire

Survivors: Young larch that are wounded by surface fires often heal and survive for centuries [10]. Trees defoliated by May slash burning may produce new needles 1 month later, and appear completely recovered within 2 years [49]. One year after underburning shelterwood units in Idaho, western larch overstory mortality was 7% [136]. After prescribed underburning of Douglas-fir-western larch forest in western Montana, western larch's radial growth was reduced in the 1st year postfire, but increased over the following 7 years, suggesting that decreased competition may have enhanced western larch growth [109].

Early Regeneration: Fires that expose mineral soil and reduce competition, especially on north-facing slopes, favor rapid and abundant western larch regeneration and dominance [2,114]. Western larch usually establishes in the 1st season after fire [2], and as much as 5 inches (13 cm) of 1st year postburn seedling growth has been reported after spring, summer, and fall burning of white fir sites on Wallowa-Whitman National Forest, Oregon [104]. In the Flathead National Forest of northwestern Montana, western larch began colonizing both wildfire and prescribed burn sites during the 1st year postfire [133,145]. Burned seedbeds from underburning in shelterwood units in Idaho produced 3 to 7 times more western larch seedlings than unburned seedbeds [136]. After clearcutting in northern Idaho subalpine fir-Engelmann spruce-menziesia type, western larch stocking was 20% on clearcuts that were burned and scarified, compared to 8% stocking on unburned clearcuts [23]. After fires in 1910 and 1919 in Coeur d'Alene National Forest, Idaho, western larch had restocked up to 200 seedlings per acre (500 seedlings/ha) on the north aspect of the study area by the fall of 1923. Western larch seedlings accounted for 83% of conifer seedlings present on all slopes and 88% of those on the north-facing slope [84]. Overstocking may result on some sites if too much mineral soil is exposed [37,67,114,123].

Old skid trails often support high densities of western larch seedlings, but the compacted soil does not allow trees to grow as well as on other sites. Good sites for potential for western larch establishment decrease as regeneration of a burned site progresses [2].

Latham and others [86] found that in general, fires that resulted in open sites, relatively free of vegetation, with full sun, moving shade, and a mineral soil seed bed favored the development of western larch forests. In these conditions, western larch seedlings were generally able to establish quickly and grow taller than other vegetation. Where tree establishment was delayed, however, shrubs were able to establish and suppress western larch.

Competition and Succession: Following fire, western larch must establish rapidly. Insufficient sunlight or exposed mineral soil will delay western larch establishment, allowing development of shrubs or more shade-tolerant tree species [2,148]. If the area does not burn again, shade will prevent western larch regeneration, and other species will eventually replace western larch [85,116]. Generally, stand-replacing fires favor western larch over its competitors because western larch is most likely to survive and postfire survivors will provide an onsite seed source, while less fire-resistant competitors must rely on offsite sources or unburned islands [1,10,135]. Low to moderate intensity fires thin out competitors [10,30]. The species may dominate the area for 150-350 years in the absence of fire [10,135].

Western larch and lodgepole pine are early seral species that often compete in the same recently burned areas. In general, lodgepole pine performs better on drier or more exposed sites [135]. Due to western larch's later age of 1st seed production and longer lifespan, it may be favored over lodgepole pine on sites that burn less frequently [138]. Western larch-lodgepole pine stands in grand fir sites of northwestern Montana with as little as 10% western larch overstory can eventually be dominated by western larch [1]. In Coram Experimental Forest in northwestern Montana, single high intensity burns in western larch-Douglas fir habitat thinned the overstory and favored regeneration of western larch, Douglas-fir and lodgepole pine, while multiple severe burns tended to promote lodgepole pine [138]. Western larch benefits from periodic surface fires that kill competing shade-tolerant conifers [15].

Absence of fire: Prior to 1900, fire maintained western larch as a dominant seral species in various habitats [3,7]. Lack of periodic fires may limit western larch regeneration [37]. Fire suppression in last century has favored thickets of suppressed shade-tolerant conifers [4,7,10], which result in a decline in the vigor of all trees [10]. These sites are at risk of high-intensity wildfires [3,4,60]. Large areas in and around the western larch habitat type are now characterized by such crowded and stagnant stands [10], and fire suppression has been linked to the decline of western larch habitat in Idaho, Montana, Oregon, and Washington [10,30,60,91].

In Bear Creek Canyon of the Bitterroot Mountains, Montana, where the old western larch are prevalent and younger ones less abundant and dwarf mistletoe has infected most trees, the species is near extinction due to lack of fire or other disturbance [91]. Remaining old-growth ponderosa pine-western larch habitat in Pattee Canyon near Missoula, Montana, has a thick understory of Douglas-fir saplings and pole-sized trees. This understory could provide ladder fuels, resulting in a crown fire [60]. If fire does not occur before the remaining trees die in these areas, or if ladder fuels create a crown fire that burns intensely enough to kill the remaining trees, the western larch seed source may be eliminated. However, if a seed source remains after fire, western larch may thrive in the postfire mineral seedbed with reduced competition.

A severe fire in the Bitterroot National Forest, Idaho, killed nearly all grand fir, Douglas-fir, and western redcedar, but most western larch over 8 inches (20 cm) d.b.h. survived [73]. After low-severity surface burns in ponderosa pine forests of eastern Oregon, 64% of western larch showed no negative effects, 33% were scarred at the base with wood exposed, and 2% burned off at the base and were felled. No trees were killed by burning material around the base of the trees [94]. A model presented by Peterson and Ryan [105] predicts zero probability of western larch (13 inches (34 cm) diameter) mortality after fire with a scorch height of 33 feet (10 meters).

More info for the terms: ground fire, surface fire

Mature western larch trees are more fire-resistant than any other species in their range. (Refer to Fire Ecology or Adaptations for more information.) Unless a smoldering surface fire or ground fire girdles boles or the buds are killed by torching, mature western larch trees will survive all but the most severe fires [10,48,61]. Peterson and Ryan [105] found that death of dormant buds on burned western larch occurred 20% lower on trees than foliage death.

Seedlings and saplings of western larch are readily killed by fire [61]. They are less tolerant than those of ponderosa pine [17,89], but may tolerate low-severity underburning better than white fir (A. concolor), lodgepole pine, or Douglas-fir [155].

More info for the terms: adventitious, crown residual colonizer, initial off-site colonizer, tree

POSTFIRE REGENERATION STRATEGY [146]:
Tree without adventitious bud/root crown
Crown residual colonizer (on-site, initial community)
Initial off-site colonizer (off-site, initial community)

More info for the terms: crown fire, fire frequency, fire-resistant species, frequency, fresh, ladder fuels, lichen, litter, relict, severity, surface fire, tree, understory fire

Western larch is considered the most fire-resistant tree in its range [10,17,24,51,89,137]. Fire is an important part of western larch's ecology; without fire or other stand replacing disturbance, western larch will not regenerate successfully and will eventually be replaced by more shade-tolerant species [116].

Fire adaptations: Western larch has many adaptations that enhance its ability to either survive fire or to quickly colonize recently burned areas. While seedlings, saplings, and poles are somewhat susceptible to fire, trees that are 150 to 200 years old or older are able to survive all but the most severe fires [24,116]. It is common for a handful of mature western larch trees to be the sole survivors after fire [24]

Surviving fire: Western larch's extremely thick basal bark protects its cambium from overheating [10,24,48,49,92,116,126,143,155]. Low resin content and light lichen growth also decrease flammability [10,116,143]. Western larch's characteristic high, open crown; open stand habit; and self-pruning lower branches minimize ladder fuels and risk of crown fire [10,24,48,49,59,116,143]. Its deep roots are protected from surface and ground fires [24,49,59,143]. In a synthesis of the literature on northwestern tree species, Minore [93] ranked western larch's bark in the most fire resistant category and its foliage in the least resistant category. He ranked western larch the most fire resistant tree in British Columbia, Washington, Oregon, and Idaho.

Needles of western larch are less flammable than other species' due to their small size. Because they are never more than 5 months old, they maintain a higher water content than other conifers' needles that are replaced every 2 or 3 years [10,24,49,116,143]. Since western larch replaces its needles annually anyway, it is better adapted to defoliation than other conifers. In fact, after defoliation early in the season western larch trees often will produce a 2nd set of needles from heat-resistant woody buds and epicormic branches [10,17,36,48,89]. The small needles also minimize accumulation of surface litter at tree bases [24].

Postburn colonization: Western larch survivors quickly reseed burned-over areas; on mineral soil seedlings develop rapidly and outgrow competitors [10,48,58,85,116,126]. Fire-killed trees may contribute to seeding if fresh cones in the burned crown mature and disperse seed [10]. Seeds are very light and long-winged, allowing trees in nearby stands to reseed even if no onsite seed source is present [10,48]. Since western larch is a very long-lived and fire-resistant species, a potential seed source remains in the area for centuries once it has established [13].

FIRE REGIMES: Wildfires have occurred in western larch forests for over 10,000 years [10,30]. Barrett and others [20] suggest 2 FIRE REGIMES for western larch forests: 1) 25-75 year intervals between mixed-severity fires, and 2) 120-350 year intervals between primarily stand-replacing fires. While the species is primarily associated with these regimes, frequent surface FIRE REGIMES can also support western larch populations [8]. Frequency and severity of fires vary with elevation, aspect, and habitat type.

Frequent understory fires: Warm, dry sites at the lower elevations of western larch's range in western Montana have been characterized by frequent, low-intensity surface fires occurring at 10 to 30 year intervals. These habitat types include Douglas-fir and grand fir. Stand replacing fires occurred in some of these stands at 150- to 400-year intervals [7,10,60]. 

In ponderosa pine-western larch habitat in Pattee Canyon near Missoula, Montana, fire scars indicate a mean fire return interval of 7.1 years from 1557 to 1918. Fire occurred an average of every 5 to 10 years from 1750 to 1850, and in 10 to 20 year intervals from 1850 through 1900. After 1900, intensity and frequency of fires were reduced until the late 1900s, when high intensity fires swept through north and south slopes of the canyon [60]. 

In the Flathead National Forest of western Montana, underburning occurred on average every 20 to 30 years in even-aged ponderosa pine-western larch stands before 1900, with stand replacing fires occurring at 150- to 400-year intervals. From 1735 to 1900 in the grand fir habitat type of western Montana, an average fire return interval of 17 years (range 3-32) maintained western larch as the most abundant tree followed by lodgepole pine and Douglas-fir. Western larch was also found on 3 Douglas-fir habitat type sites with average intervals of 7 (range 2-28), 16 (range 4-29), and 19 (range 2-48) years [15].

Arno's [8] literature review reported that understory FIRE REGIMES prior to 1900 in ponderosa pine-mixed conifer habitat types of western North America favored western larch and other fire resistant species such as ponderosa pine and Jeffrey pine. From 1600 to 1900 in several relict habitat types where western larch occurs in western Montana, fire return intervals averaged 27 (range 17-35) years in the Douglas-fir-big huckleberry (V. membranaceum) type, 25-30 years in the Douglas-fir-dwarf huckleberry (Gaylussacia dumosa) type, and 24 (range 9-42) years in the subalpine fir-queen cup beadlily (Clintonia uniflora) type [7].

Mixed-severity fires: Much of the northern Rocky Mountains are characterized by 30- to 100-year-interval fires of varying severity, which favor open stands of western larch and Douglas-fir in Douglas-fir, western larch, and lodgepole pine habitat types [8,14]. In the Bob Marshall Wilderness, Montana, western larch-Douglas-fir-lodgepole pine and ponderosa pine forest types were historically maintained by mixed severity fire regimes. Many live western larches in this area had 1 to 3 fire scars, and 1 was found with 4 scars. Fire return intervals in this area are nearly twice as long as historic mean intervals [14].

In western larch-Douglas-fir forests of the North Fork of Glacier National Park, Montana, mean fire frequency from 1650 through 1935 was 36 years in relatively dry sites and 46 years in relatively moist sites. In the drier areas, up to 7 understory fires occurred between stand-replacing fires, which occurred at a mean interval of 141 years. Only 1 or 2 understory fires occurred between the less frequent stand-replacing fires (186-year mean intervals) on moister sites [20].

On dry subalpine fir and cool, moist Douglas-fir habitat types that were codominated by western larch, lodgepole pine, and Douglas-fir, average fire return intervals ranged between 30 and 75 years. Severity varied from understory burns to stand-replacing fires [10].

Infrequent stand-replacement fires: In western larch-Douglas-fir forests of northwestern Montana, average fire return intervals from 1735 to 1976 were 120 years in valleys and montane slopes and 150 years for subalpine slopes. Most fires were small and of moderate intensity with occasional patches of high intensity. Though some stands had as many as 6 fires during the period studied, most stands had only 1. A trend of decreasing mean frequency with increasing elevation was noted, and fires on north aspects were more intense and less frequent. Multiple burns occurred primarily on south-facing slopes. In these forests, single burns of low to moderate intensity thinned the overstory and tended to favor regeneration of mixed conifers with patches of seral species, while single intense burns resulted in even-aged forests. Intense, repeated burns (fire return interval <50 years) created shrubfields or homogeneous stands, usually of lodgepole pine [35].

From 1650 to 1935, relatively moist western larch-Douglas-fir forests in Glacier National Park had stand replacement fires at mean intervals of 140 to 340 years [20]. In subalpine fir and Engelmann spruce habitat types in the Middle Fork Drainage of Glacier National Park, Montana, lodgepole pine and western larch stand-replacement intervals were generally 150 to 300 years but as short as 25 years [19], and in grand fir habitat in the Swan Valley of Montana, stand-replacing fires occurred in average 150-year intervals, ranging from less than 20 to more than 300 years [2].

Moist sites of grand fir, subalpine fir, western redcedar, and western hemlock habitat types, which were dominated by western larch, lodgepole pine, Douglas-fir, and Engelmann spruce, burned primarily as stand-replacement fires with average fire return intervals of 120 to 350 years [10].

In western redcedar-hemlock (Tsuga) forests of northern Idaho, fire free intervals ranged from 50 to 100 years with varied intensity. In subalpine fir habitat type, low to medium intensity fires occurred at intervals greater than 150 years [9].

FIRE REGIMES for plant communities and ecosystems where western larch is a common associate are summarized below.

Community or Ecosystem Dominant Species Fire Return Interval Range (years) grand fir Abies grandis 35-200 [8] Rocky Mountain juniper Juniperus scopulorum 103] western larch* Larix occidentalis 25-350  [2,4,6,7,8,9,10,14,15,19,20,35,60] Engelmann spruce-subalpine fir Picea engelmannii-Abies lasiocarpa 35 to > 200 [8] Rocky Mountain lodgepole pine* Pinus contorta var. latifolia 25-300+ [8,113] interior ponderosa pine* Pinus ponderosa var. scopulorum 2-30 [8,18,87] Rocky Mountain Douglas-fir* Pseudotsuga menziesii var. glauca 25-100 [8,11,15] Oregon white oak Quercus garryana < 35 western redcedar-western hemlock Thuja plicata-Tsuga heterophylla > 200 mountain hemlock* Tsuga mertensiana 35 to > 200 [8] *fire return interval varies widely; trends in variation are noted in the species summary

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More info for the terms: competition, presence, relict, resistance, wildfire

Western larch is the least shade tolerant conifer in its range [11,45,46,48,116]. As such, it is a seral species whose populations have been historically maintained by disturbances such as wildfire and glacial retreats [45,46,116,126] and is therefore usually found in even-aged stands [116]. It is an aggressive pioneer species after fire or other major disturbance [11,46,61,88] and competes best on moist sites [48,61]. In drier environments where fires are frequent, western larch may form a "fire climax" [152].

Western larch uses nitrogen more efficiently than evergreen trees, reducing its dependence on soil for nitrogen and increasing its effectiveness as a pioneer in disturbed, infertile habitats [56,149]. This aggressive pioneer quickly colonizes disturbed areas and grows rapidly, remaining taller than its associates for approximately 100 years [45,46,116,126]. Western larch's rapid height growth may indicate allocation of resources to early growth rather than early seed production, which would explain the species' relatively advanced age of 1st reproduction compared to other early successional species. Western larch extension growth was significantly greater than that of 6 other northwestern conifers. This characteristic and low shade tolerance were both associated with early successional species studied [152].

In the absence of disturbance, shade tolerant associates form understories that shade out future generations of western larch seedlings [116]. However, western larch's long lifespan and resistance to damage from fire and pathogens accounts for the presence of relict trees in late-successional stands that can repopulate the stand if fire or other disturbance removes competition and opens the canopy [45].

More info for the terms: competition, litter, monoecious, natural, tree

Breeding system: Western larch is monoecious with both staminate and ovulate cones distributed throughout the crown [115,116].

Pollination: Western larch pollen is distributed by wind and is less abundant than that of other conifers. Owens [101] described the physiological details of pollination in western larch.

Seed production: Western larch cone production may begin as early as age 8 though it is unusual on trees less than 25 years old. Heavier crops usually begin at approximately 40 to 50 years of age and continue for 300 to 500 years [116,130]. Trees usually produce cones annually, but crop size varies with year and location; heavy cone crops occur every 5 years on average, with fair to poor crops in other years [115,121]. Shearer and Carlson [121] reported an annual average of 1,393 potential cones per tree over a 6-year period. Because western larch cones are borne throughout the crown, the size of the crop generally corresponds to the size of the crown [115,116,117]. Shearer and Kempf's [132] literature review indicated that the number of cones also increases with increased spacing of trees.

Western larch seeds are small and light, just 137,000 to 143,000 per pound (301,00-315,00/kg) [12,115,154]. On average each mature cone produces 39 seeds, but some may contain as many as 80, and mature stands of western larch may produce more than 0.5 million seeds per acre (1.2 million seeds/hectare) [115]. Roe [111] described a method for estimating the size of western larch seed crops up to 1 year in advance.

Viability of seeds typically increases with crop size and decreases with tree age [115]. Inviable seed results from lack of pollination, inviable pollen, lack of fertilization, later ovule abortion, or embryo abortion [102]. Over a 6-year period, Shearer and Carlson [121] found that 4% of potential seeds at the time of bud burst matured as filled seeds.

Seed dispersal: Most of western larch's small, light, long-winged seeds are distributed within 328 feet (100 m) of the parent. However, depending on wind conditions, they may be dispersed up to 820 feet (250 m) or more [116]. This distance is comparable to that of Engelmann spruce seeds, but is longer than Douglas-fir and subalpine fir [115]. Seed spread rate is considered moderate [154].

Seed banking: Western larch seeds are viable only until the year following fertilization [117].

Germination: Seeds of western larch germinate well on a variety of seedbeds and aspects [117], but Stoehr [147] found that germination and survival was greatest in mineral soil. In a synthesis of literature on northwestern trees, Minore [93] ranked western larch germination and survival in the highest category for mineral seedbeds, in the middle category for burned seedbeds, and in the lowest category for organic seedbeds. The ideal temperature for germination is 80° Fahrenheit (27° C), but germination can occur at temperatures as low as 65° Fahrenheit (18° C). Germination occurs at or above the soil surface. Natural stratification during winter results in rapid, complete germination. Spring-sown western larch seeds without stratification germinate slowly and erratically; some do not germinate until the following season [115]. Oswald [100] reported seed predation and shade both had negative effects on germination rates of western larch, though shading was not a significant factor. Shade appears to be more important as seedlings develop.

Seedling establishment/growth: On average 1 western larch seedling will establish for every 53 seeds produced and dispersed [127]. Seedlings grow rapidly and vigorously [115,154], averaging 2 inches (5 cm) of growth during the 1st season and 12 inches (30 cm) per year over the next 4 years. Western larch seedlings grow faster than all major associates except lodgepole pine, and the species grows faster than any other Rocky Mountain conifer until 100 years of age [12,115].

Site variation: Site requirements for establishment and growth of western larch seedlings are more specific than those for germination. Seedlings are well adapted to the mineral soil and sunlight of exposed seedbeds, such as those created by burning or mechanical scarification. They do not thrive in areas with undisturbed litter, humus, sod, or heavy root competition [12,54,115,116,117,123]. Overly dense stands slow growth. For the 1st few years shaded seedlings usually grow faster than those in full sunlight; thereafter, seedlings in full sunlight outgrow shaded seedlings. North, northwest, and northeast exposures and gentle to flat topography are best for seedling survival; high surface temperatures on south and west exposures may kill many seedlings [115].

Mortality: Seedling mortality is usually highest in the 1st season; losses after year 3 are minimal [115]. Biotic factors, such as fungi, birds, and rodents, cause the most 1st year seedling deaths early in the season, but drought is more detrimental after mid-July [115,117]. Newly germinated seedlings were killed by high soil-surface temperatures (>130° Fahrenheit (54° C)) in Montana, and these effects were most severe on western and southern exposures [117,122].

Asexual regeneration: Western larch does not reproduce by sprouts, but propagation by cuttings has been successful [115].

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More info for the term: phanerophyte

RAUNKIAER [107] LIFE FORM:
Phanerophyte

More info for the term: tree

Tree

Larch is the most shade-intolerant  conifer in the Northern Rockies. Only during the seedling stage can it  tolerate partial shading. If larch is overtopped its crown rapidly  deteriorates, and its vigor declines severely.

    Because of its intolerance to shade, larch grows in even-aged stands or  age-classes. Its primary associates are usually the same age as larch but  often give the appearance of being younger because they grow slower than  larch and form the lower strata in the stand. As larch stands mature,  however, shade-tolerant associates continue to establish and form younger  understories.

    Fire is essential to the maintenance of western larch in natural forest  stands. Most fires that occur on mountain slopes are usually small and of  low or moderate intensity (8). Fire intensity, however, increases on steep  slopes with heavy fuels, or on dry ridgetops. These fires thin stands,  reduce fuels, rejuvenate undergrowth, and prepare seedbeds that promote  mixed conifer stands with small pockets of regeneration dominated by seral  species, particularly western larch. Intense fires often create definite  even-aged stands. At Coram, multiple burns occurring at less than 50-year  intervals favor lodgepole pine or shrub fields. Historically, within the  mixed conifer/pinegrass communities of the Blue Mountains of Oregon,  underburns occur at 10-year intervals and maintain western larch and other  seral species in the stands (15). Here, all species, including western  larch, often overstock and can stagnate unless periodic fires release some  trees. Without fire, grand fir and Douglas-fir replace the seral species.

    Although larch normally remains in the dominant position, understory  trees and other vegetation vigorously compete with larch for available  water and nutrients. In one harvest-cutting study, diameter growth of  residual mature seed trees after logging increased 67 percent over  pre-logging growth (44). When all understory trees were also cut, the seed  trees increased an additional 36 percent in diameter increment.

    Even-aged silviculture systems of shelterwoods, seed-tree cuttings, and  clearcuts best fit the ecological requirements of larch forests. They  provide an adequate seed source and the microsite conditions needed for  establishing the new seedlings. They are also compatible with the site  preparations of prescribed burning 'or scarification needed to reduce the  duff layers and vegetative competition for the new seedlings. Prescribed  burning most closely approximates the natural wildfires that historically  have perpetuated larch forests. No detrimental impact on site quality has  been attributed to harvesting or prescribed fire on the soil microflora  (16).

    Conversely, uneven-aged silviculture systems have limited utility in  most larch forests. Not only does the residual stand show little overall  growth response after partial cuttings, the growth increases that do occur  are mainly on the more tolerant and generally less desirable species, such  as subalpine fir. In addition, partial cuttings discriminate strongly  against larch and its shade-intolerant associates in the regeneration  process, and larch becomes a minor stand component in stands it formerly  dominated. Prescribed burning or scarification needed to regenerate larch  are very difficult in partial cuttings. For management considerations  other than timber production, such as esthetics or wildlife, there may be  rationale for uneven-aged silviculture systems in some larch forests. Even  here, however, it should be recognized that these practices violate the  normal regeneration sequence in most of these forests, accelerate the  succession to tolerant species, and increase insect and disease problems.  Studies on Coram Experimental Forest have demonstrated many of the  problems with single-tree selection cuttings. Even with special care, it  is extremely difficult to use group-selection cuttings in old-growth larch  forests.

    Exceptions to the above are possible in some of the drier phases of  Douglas-fir and grand fir habitat types, particularly in the Blue  Mountains of Oregon and some lower elevation areas of western Montana.  Here, natural underburns at 20- to 30-year intervals perpetuated more  open-grown stands and allowed the establishment of western larch and  ponderosa pine regeneration under the main forest canopy (1,15).  Uneven-aged silviculture systems that mimic these natural conditions are  plausible in these types of larch forests.

    Thinning in young western larch stands, preferably before age 20,  enhances the growth of diameter and height during the juvenile years when  response potential is greatest. Drastic reduction in the densities found  in most unthinned stands is advisable. Studies in young larch show that  larch responds well in diameter, height, and crown retention under a  fairly broad range of densities after thinning, usually exceeding what  were thought to be maximum growth rates (30). Even at ages 30 to 50, larch  responds well to release (25,36). By this age, however, overstocking has  reduced the crown and response is usually delayed. Timing and extent of  response is a function of length and severity of overstocking. Individual  tree growth once lost can never be regained.

    Branch turnups following thinning can be a problem in young larch  stands. If a tree is cut off above a live branch, it may turn up, reform  the tree, and reduce the effectiveness of the thinning (35). Older larch  sometimes produce sprouts from adventitious buds on the upper bole of the  tree after thinning of older stands, but this effect may not have  practical significance. The amount of sprouting increases with the  severity of the thinning (25).

    Preliminary studies of fertilization in Montana (2) show a positive  diameter growth response to fertilization with nitrogen, but the effects  last only about 3 years. Similar studies in Idaho showed a short-term  diameter growth response to nitrogen (13), but neither study showed any  height increase.

Larch develops a deep and extensive root system,  but little information is available about its root growth. Root lengths on  first-year natural seedlings usually reach 5 cm (2 in). Under good nursery  conditions, well-developed fibrous roots 20 cm (8 in) or longer develop on  1-0 growing stock. Observations in soils under young larch stands indicate  extensive fibrous rooting in the top 50 cm (20 in), substantially less in  the 50-100 cm (20-40 in) depths, and practically none at greater depths.  Soil water depletion studies verify these observations in young larch  stands (29). Heavy rooting at depths greater than the above has been  observed along roadcuts through old-growth stands. Evaluations of roots of  windfallen overmature larch show that nearly all of them were infected  with root rots (35). Apparently, these rots play an important role in wind  stability of overmature trees, but their importance in young trees is not  known.

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Western larch's active growth occurs from May through August [115,154]. Vegetative development of western larch proceeds as follows:

Stage of Development Timing Buds begin to appear early fall [115] Buds swell, then open late March and April [121] Needle growth declines mid-May Diameter growth begins mid-May Diameter growth peaks, needle growth ends, height growth begins mid- to late June Height growth peaks mid-July Height growth complete mid-August [132]

Reproductive development in western larch proceeds as follows:

Stage of Development Timing Notes Cone initiation early summer [101,115] ---- Buds appear early fall [115] ---- Pollen and seed cone buds develop prior to winter dormancy [101,115] ---- Pollen and seed cone development begins late March and April [121] ---- Pollen and seed conelets appear mid-April to mid-May ---- Pollination late April to early June [115] ---- Fertilization June to July [102,115] Fertilization occurs 6-8 weeks after pollination. Cones mature mid- to late August Cones mature faster during warmer summers. Cone opening begins late August and early September [115,117] Long periods of cool or moist weather may delay opening [115]. 80% of seeds dispersed mid-October [115,117,121,125] Seeds dispersed later usually have lower viability [125]. Cones fall winter Some cones may remain on trees through the next summer [115]. Germination late April through early June [115] Germination roughly coincides with snowmelt and occurs 1-2 weeks before that of associates. Germination occurs earlier on lower elevation or exposed sites and later at upper elevations or in sheltered areas [117].

Larch does not reproduce by sprouts.  Cuttings have been successfully rooted by researchers at the Intermountain  Forest and Range Experiment Station, but methods have not been fully  tested at this time. One technique requires cutting 8 to 10 cm (3 to 4 in)  scions from young larch trees, dipping the lower portion of the cutting in  a powder mixture of 0.8 percent indolebutyric acid and 10.0 percent Captan  50 wettable powder (mixed with talc), and placing them in a rooting   chamber at about 24° C (75° F). Researchers at the Intermountain  Station have successfully grafted western larch.

Western larch is a seral species well  adapted to seedbeds exposed by burning (9) or mechanical scarification  (35,40). Seedbeds of undisturbed litter, humus, sod, and areas with heavy  root competition are poor for larch seedling survival. Most seedling  losses occur the first growing season- after 3 years seedling losses are  minor (35). For example, studies on areas favorable for larch show that 54  percent of the seedlings survived the first season; 85 percent of the   remaining seedlings survived the second season; and by the fifth season  the remaining seedlings survival was 94 percent. In other studies, an  average of 39 percent of the larch seedlings survived the first 3 years  (44).

    Seedling survival is affected mostly by biotic factors early in the  growing season and by physical factors late in the season. Until about  mid-July mortality is caused primarily by fungi, rodents, birds, and  insects. Most losses of first-year seedlings, particularly those growing  on duff, are caused by fungi, usually immediately after germination.  Seedlings growing on mineral soil seedbeds are far less susceptible to  fungi than their counterparts growing on duff under both full sun and  partial shade. Under full shade, however, susceptibility on the two types  of seedbed is reversed (44). Seedling losses to animals, insects, and  birds are relatively minor overall but may be heavy in specific locations  and years.

    Insolation is the most important physical factor affecting larch  seedling survival (38). High soil surface temperatures exceeding 57°  C (135° F) are not uncommon starting in late June, resulting in heat  girdling of seedlings at the soil-air interface. Again, duff is the least  desirable seedbed, with lethal temperatures occurring earlier in the  season and on more days. Lethal soil temperatures are reached most  frequently on duff, less on burned mineral soil, and least on scarified  mineral soil. On south and west slopes, soil surface temperatures exceed  79° C (175° F), and few larch seedlings survive regardless of  the type of seedbed (38).

    Drought is the major physical factor affecting mid-to late-season  seedling survival. Unlike insolation, drought losses are heaviest in full  shade because of the heavy competition for moisture by all the associated  tree and understory vegetation.

    Although aspect affects germination very little, it has a pronounced  effect on seedling survival. North, northwest, and northeast exposures and  gentle to flat topography provide the most favorable conditions for larch  seedling survival. High surface temperatures and droughty conditions on  the south and west exposures preclude survival of any significant number  of larch seedlings. As a result, larch is either absent or but a minor  stand component on hot, dry slopes.

    Larch seedlings grow about 5 cm (2 in) the first growing season. In  shade, root penetration may average only 2.5 cm (1 in) the first year,  while its counterparts growing in the sun or partial shade may have 23 cm  (9 in) roots. Seedlings growing in partial shade usually grow faster in  height than seedlings in full sunlight for the first few years, but faster  in full sunlight after that.

    Larch seedlings break dormancy very easily. Buds usually burst by late  April, well before those of any other native conifers. Shoot growth starts  from late May to mid-June.

    Larch seedlings grow rapidly in spite of the relatively short growing  season of the Northern Rockies. Average annual height growth of about 30  cm (12 in) for the first 4 years is common (44). Of its major associates  only lodgepole pine matches the rapid juvenile height growth of western  larch. Douglas-fir seedlings grow at about one-half the rate of larch, and  Engelmann spruce and subalpine fir seedlings grow at about one-fourth the  rate of larch (28).

Larch is a good seed  producer, but cone crops vary substantially by year and location.  Long-term records of larch seed production in Montana show that good seed  crops are produced at about 5-year intervals with fair to poor crops in  the intervening years (44). Two good crops or several poor crops, however,  may occur in close succession. Overall, the ratio of good or fair to poor  seed crops is about 1 to 1.

    Cone production is infrequent on larch trees less than 25 years old,  although trees as young as 8 years occasionally produce cones. Larch  starts bearing abundant cone crops from 40 to 50 years and continues  bearing heavily for 300 to 500 years (35). Only dominants and codominants  produce significant numbers of cones (44).

    Cone production usually is a function of crown size because larch bears  cones throughout the crown. Trees with the largest crowns produce the most  cones. During a good cone year, production ranged from a low of 56 cones  in one tree with 45 major branches to a high of 2,090 cones in another  tree with 95 major branches. Also, vigorous, full-crowned, mature trees  averaging 56 cm (22 in) in diameter produced about five times as many  seeds as 36-cm (14-in) trees in the same stand and age class (44).

    A mature cone may have as many as 80 filled seeds per cone, but the  average is about half that number (39). Seed viability is related to  cone-crop size, ranging from a low of 5 to 10 percent viability in poor  crops to 70 to 80 percent in good crops. Young trees usually produce seeds  of higher viability than overmature trees.

    Larch seeds are small and lightweight, averaging 302,000/kg (137,000/lb)  (45). Because of their relatively large wing, they are dispersed to  greater distances than the heavier seeds of Douglas-fir and subalpine fir,  but to about the same distance as the light seed of Engelmann spruce (37).  Larch seed may be dispersed 240 m (787 ft) from clearcut boundaries under  normal wind conditions (fig 1). Although the seeds traveling that distance  are only about 5 percent of that falling within the timber, they may  amount to 100,000/ha (40,000/acre) in a heavy seed year-more than is  adequate to restock favorable seedbeds. Overstocking often occurs near the  seed source when bare soil is exposed. Seeds are disseminated more  uniformly in seed tree and shelterwood cuttings than in clearcuts.

     
Figure 1- Dispersal characteristics of sound western  larch seed from a 
seed source along a clearcut boundary.

    Seed production in mature natural stands of larch may exceed 1.2 million  seeds per hectare (0.5 million seeds/acre) in a heavy seed crop. Records  at Coram. Experimental Forest indicate that small rodents eat only about 1  to 3 percent of the seeds during the overwintering period (41). In  contrast, rodents usually feed heavily on the larger seeds of Douglas-fir  and ponderosa pine during this same period.

    Larch seed germinates about the time of snowmelt from late April to  early June, usually 1 to 2 weeks before associated tree species (38).  Germination is epigeal (45). Natural stratification of larch seeds during  the winter prompts rapid and complete germination. Without stratification,  spring-sown larch seeds germinate slowly and erratically, with some seeds  holding over until the next season. Artificial stratification methods  using cold-moist conditions work well for preparing seed for field  germination. These same seed treatments, as well as those using  stimulants, such as hydrogen peroxide, are particularly useful for testing  germinative energy and capacity (26). Air temperatures of about 27° C  (80° F) are ideal for larch seed germination, but seeds germinate at  temperatures 10° to 15° C (17° to 27° F) cooler than  that.

Western larch is monoecious; both  staminate and ovulate flowers develop throughout the crown. Buds are found  at the end of short spurlike lateral branchlets. Vegetative buds are  smaller than flower buds-usually about 2.5 to 3.0 mm (0.10 to 0.12 in) in  diameter, whereas flower buds range from about 3.0 to 4.8 mm (0.12 to 0.  19 in) in diameter. Ovulate buds are one to one and one-half times longer  than they are wide and are rounded or conical on the end. Staminate buds   are usually globose and about one and one-half to two times longer than  wide. Vegetative and flower buds can be detected early in the fall, about  1 year before subsequent cone crops mature. Methods of sampling buds and  conelets have been devised for forecasting larch seed crops on individual  trees, as well as stands (24).

    Pollen and seed conelets appear several days before vegetative buds  open-usually from about April 15 to May 15 (44). Conelets are generally  very conspicuous, varying from bright red to green. Pollination occurs in  late May and early June (33). Cones complete their development in one  season and mature by mid- to late-August, reaching 2.5 to 4.5 cm (1.0 to  1.8 in) in length.

    Cones usually begin to open by early September, but in cool-moist  summers cone opening may be delayed a month or longer. More than 80  percent of the seeds usually are dispersed by mid-October (44). Cones open  when they have dried to a moisture content of 35 to 40 percent, opening at  the same time on individual trees, but varying substantially among trees  in the same stand (39). Cones usually fall from the tree during the  following winter, but many may stay attached through the next summer.

Western larch is long-lived and is the largest  of the world larches (20). Trees exceeding 230 cm (90 in) d.b.h. and 900  years of age have been found (44). Larch normally reaches 30 to 55 m (100  to 180 ft) in height at maturity and occasionally exceeds 61 m (200 ft).

    Larch grows faster in height than any other conifer in the Northern  Rockies for the first century, giving this highly shade-intolerant species  the height advantage it needs to survive. For the first 50 years, larch  and lodgepole pine height growth are similar, but thereafter lodgepole  height growth declines in comparison with larch.

    Differences in height growth of larch and its associated species are  readily apparent at early ages. Both larch and lodgepole pine start off  faster than their associates. Studies on good quality sites on Coram  Experimental Forest in Montana show larch and lodgepole pine growing at  about twice the rate of Douglas-fir and three to four times faster than  subalpine fir and Engelmann spruce for the first 20 years. On wetter sites  in northern Idaho, larch and lodgepole pine typically grow much faster  than western white pine, western hemlock, and western redcedar in  unthinned natural stands for the first half century. In thinned stands,  however, differences in height growth of western white pine and larch are  nominal. By age 100, the height growth advantage larch holds over its  associates typically becomes less pronounced (35,10).

    Site productivity accounts for the largest share of the variation in  height growth of larch throughout its range. Site index curves for larch  (base age of 50) show heights at age 100 ranging from 20 m (65 ft) on low  sites to 40 m (130 ft) on high sites (table 2). Average site indices for  larch on different ecological habitat types are given in table 3.

    Table 2- Height of average dominant and co-dominant  western larch by age and site index            ______Site index at  base age 50 years______      Age  12.2 m or 40 ft  18.3 m or 60 ft  24.4 m or 80 ft            yr  m  m  m        20    3    4    6        40    9  14  19        60  14  21  29        80  17  26  35      100  20  30  40      yr  ft  ft  ft        20    9  14    19        40  31  47    63        60  47  70    94        80  57  86  115      100  65  97  130              Table 3- Average site incdices for larch (21,35)           
Ecological habitat type  Average site index at 
base age 50 years              m  ft      Northern Idaho and Washington:¹            Abies lasiocarpa-Xerophyllum tenax  14.9  49        Abies lasiocarpa-Pachistima myrsinites  17.7  58        Tsuga heterophylla-Pachistima  myrsinites;              Thuja plicata-Pachistima  myrsinites; Abies              grandis-Pachistima  myrsinites  20.1  66        Pseudotsuga menziesii-Physocarpus  malvaceus  18.9  62        Pseudotsuga menziesii-Calamagrostis  rubescens  16.8  55      Montana:            Pseudotsuga menziesii-Vaccinium  caespitosum  18.0  59        Pseudotsuga menziesii-Physocarpus  malvaceus  17.4  57        Pseudotsuga menziesii-Linnaea borealis  16.8  55        Picea-Vaccinium caespitosum  22.6  74        Thuja plicata-Clintonia uniflora  19.2  63        Tsuga heterophylla-Clintonia uniflora  24.4  80        Abies lasiocarpa-Clintonia uniflora  19.2  63        Abies lasiocarpa-Linnaea borealis  17.1  56        Abies lasiocarpa-Menziesia ferruginea  20.4  67        Abies lasiocarpa-Xerophyllum tenax  15.5  51      ¹Based on  Daubenmire's classification (6).        Physiographic position, directly interrelated with habitat type, also  influences height growth. Larch grows most rapidly in height on the deep,  moist soils of valley bottoms and lower north and east slopes, but poorly  on the upper south and upper west slopes (35):

      Physiographic class  Average site index        m  ft      Valley bottoms  18.9  62      Midnorth and mideast facing slopes, lower south and  lower west facing slopes and benches 
 
18.0 
 
59      Upper north and upper east facing slopes 
  17.4 
  57      Midsouth and midwest facing slopes 
  16.2 
  53      Upper south and upper west facing slopes 
  13.4 
  44        Seedbed conditions at the time of seedling establishment influence  height growth in the formative years (27). Studies on Priest River  Experimental Forest in northern Idaho showed that on the average  2-year-old larch seedlings were twice as tall on burned seedbeds as they  were on bare mineral or duff-covered soil (14). Subsequent studies on  Coram Experimental Forest showed that these height growth differences  persisted into the teenage years, with larch growing about one-third  faster on burned seedbeds than on scarified or undisturbed seedbeds (35).  These differences may be due to changes in nutrient availability, water  infiltration into the soil, or competing vegetation. Microchemical tests  showed increased levels of manganese, magnesium, nitrogen, phosphorus, and  calcium in the upper soil layers of burned seedbeds (14).

    Stand density also affects height growth very early in the life of the  stand (27). Heavy overstocking is common in young stands with densities  sometimes exceeding 86,500 trees per hectare (35,000/acre). In a  9-year-old stand at Coram Experimental Forest for example, dominant larch  were growing a third faster in height in stands with 12,400 trees per  hectare (5,000/acre) than they were in stands with 86,500/ha  (35,000/acre). Thinning these overstocked stands relieved this height  growth suppression, but even the dominant trees in unthinned stands  continued to grow well below their potential in height (30). By age 24,  dominant trees in the thinned stands averaged more than 9 m (30 ft) tall,  but their counterparts in the unthinned stands averaged 15 to 20 percent  less (29).

    Diameter growth measured at breast height (1.37 m or 4.5 ft) for larch  largely parallels height growth and is affected by many of the same  factors. Larch has the potential for rapid diameter growth, but  overstocking, insects, and dwarf mistletoe often prevent full realization  of this potential.

    Potential diameter growth curves have been developed for western larch  on different combinations of habitat type and site index to provide a  basis for evaluating tree and stand conditions (table 4) (35).

    Table 4- Potential d.b.h. of western larch trees at age  50 and at age 100 years by ecological habitat type and site index (35)          ______________Site  index at base age 50 years_____________       
Ecological habitat type   
Age  12.2 m or 40 ft  18.3 m or  
60 ft  24.4 m or  
80 ft              yr  cm  cm  cm      1. Abies lasiocarpa-Xerophyllum tenax    50  13.7  19.3  -        100  25.1  33.8  -      2. Pseudotsuga menziesii-Physocarpus malvaceus    50  14.5  19.8  -            and Calamagrostis  rubescens  100  26.7  35.0  -      3. Abies lasiocarpa-Pachistima myrsinites    50   -¹  20.3  25.9        100  -  35.8  44.7      4. Abies grandis-Pachistima myrsinites    50  -  20.6  26.2        100   -   36.6  45.2      5. Tsuga heterophylla-Pachistima myrsinites    50  -  20.8  26.2            and Thuja  plicata-Pachistima myrsinites  100  -  36.8  45.2        yr  in  in  in      1. Abies lasiocarpa-Xerophyllum tenax    50    5.4    7.6  -        100    9.9  13.3  -      2. Pseudotsuga menziesii-Physocarpus malvaceus    50    5.7    7.8  -            and Calamagrostis  rubescens  100  10.5  13.8  -      3. Abies lasiocarpa-Pachistima myrsinites    50  -    8.0  10.2        100  -  14.1  17.6      4. Abies grandis-Pachistima myrsinites    50  -    8.1  10.3        100  -  14.4  17.8      5. Tsuga heterophylla-Pachistima myrsinites    50  -    8.2  10.3            and Thuja  plicata-Pachistima myrsinites  100  -  14.5  17.8      ¹Dashes indicate  that values are outside the data base.        These projections, based on relatively open trees, show larch at, age  50, reaching diameters ranging from a high of 26 cm (10.3 in) on high to  14 cm (5.4 in) on low quality sites; at age 100, 45 cm (17.8 in) to 25 cm  (9.9 in).

    Larch diameter growth is very sensitive to stand density. For example,  in 9-year-old stands on Coram Experimental Forest, overstocking of 86,500  trees per hectare (35,000/acre) had already restricted diameter growth of  the dominant trees to half that of their counterparts in stands with  12,400/ha (5,000/acre) (27). At age 19 and 24, dominant trees in these  unthinned stands (with about 37,100/ha or 15,000/acre) continued growing  at about half the rate of their counterparts in thinned stands (with about  1,000 trees per hectare or 400/acre). For example, at age 24, dominant  trees in thinned stands averaged nearly 13 cm (5 in) compared to about 8  cm (3 in) for dominants in unthinned stands (29). Elsewhere, 30- to  50-year-old stands in Montana showed about the same diameter  relationships, with crop-trees in unthinned stands growing at about half  their potential (25).

    Basal area increases rapidly to about age 40 years, decelerates, and  nearly levels off after age 100. At age 100, basal area of larch forests  approaches 69 m²/ha (300 ft²/acre) on high quality sites and  about 46 m²/ha (200 ft²/acre) on low quality sites. On high  sites, the average annual increase in basal area is about 0.7 m²/ha  (3 ft²/acre) for the first century. Average increase during the 100-  to 200-year period is only about one-tenth the rate noted in the first 100  years. As basal area stocking approaches site potential, increment drops  off rapidly-the site is fully occupied.

    Larch forests can produce heavy timber volumes. The increase in volume  follows a similar pattern as basal area but peaks later. Because of their  influence on diameter and height growth, site quality, age, and stocking  level play the major roles in volume yield. Projected cubic yields for  larch forests at age 100 range from 308 m³/ha (4,407 ft³/acre)  on low quality to 813 m³/ha (11,608 ft³/acre) on high quality  sites (table 5). With full stocking (but not overstocked), 544 m³/ha  (7,765 ft³/acre) is a reasonable objective by age 100 on medium  quality sites for larch forests.

    Table 5- Total volume of western larch trees 1.5 cm (0.6  in) and larger in d.b.h. (35)            _____Site index at  base age 50 years_____      Age   12.2 m or 40 ft  18.3 m or 60 ft  24.4 m or 80 ft            yr  m³/ha      20   ¹17    30      45      40  105  184    275      60  191  336    502      80  258  454  ¹678      100  308  544  ¹813      yr  ft²/acre      20   ¹246     434        648      40  1,494  2,632      3,934      60  2,724  4,801      7,176      80  3,680  6,484     ¹9,692      100  4,407  7,765  ¹11,608      ¹Values in  italics are extrapolated beyond the range of the basic data.

Population Differences    No differences in cold hardiness of 1-year-old larch seedlings were  detected from 78 populations before frost in early September (23).  Regardless of geographic origin, 2-year-old seedling populations separated  by 1000 m (3,300 ft) tended to differ by 1.4 days in bud burst, 1.1 weeks  in bud set, and 8 cm (3.1 in) in height (21 percent of the height  variance) when growing in the average test environment.

    Races and Hybrids    Races of western larch are not known. Putative natural hybridization of  western larch and subalpine larch (Larix lyallii) occasionally  occurs in areas where their distributions overlap (4). Even where the  geographic ranges of the, two species overlap, usually elevations of 300 m  (1,000 ft) or more separate them. Interspecific hybrids of western larch  and Japanese larch (Larix leptolepis) were taller and more  vigorous than open-pollinated western larch progenies at the end of the  first and second growing seasons (48).

The following is a representative barcode sequence, the centroid of all available sequences for this species.

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 1
Specimens with Barcodes: 3
Species With Barcodes: 1

Year Assessed

• Needs updating

Assessor/s

Reviewer/s

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Western larch forests are valued for their multiple resource values. The  seasonal change in hue of larch's delicate foliage from light green in the  spring and summer, to gold in the fall, enhances the beauty of these  mountain forests.

    Because larch is an aggressive pioneer species, it quickly reforests  areas denuded by natural or man-caused disturbances, providing protection  for those important watersheds in the Columbia River Basin. Western larch  is an important component of high water-yielding forests-areas where  management can influence water yield through harvest cuttings (19) and  young stand culture (29).

    Larch forests provide the ecological niches needed for a wide variety of  birds and animals. Hole-nesting birds comprise about one-fourth of the  bird species in these forests, and studies on Coram Experimental Forest  show that broken-topped larch is a preferred site for the hole-nesters  (18). Deer, elk, moose, and the black and grizzly bear are widespread and  numerous throughout the range of larch.

    Larch timber is used extensively for lumber, fine veneer, long-straight  utility poles, railroad ties, mine timbers, and pulpwood (35). Larch wood  is strong and hard and contains about 4 to 23 percent arabinogalactan. It  is the best domestic source of this water soluble gum used for offset  lithography and in food, pharmaceutical, paint, ink, and other industries.  Arabinogalactan has the consistency of honey and contains 16 percent  volatile pinene and limonene (44).

    Timber harvesting practices in larch forests are now utilizing more of  the woody biomass formerly left in the woods after logging. Studies in the  last decade have aimed at characterizing this biomass and the  environmental consequences of removing biomass from larch forests (46).  Typically, large volumes of standing live and dead tree biomass are found  in old-growth larch forests (3). For example, of the 512 m³/ha (7,318  ft³/acre) found on a larch study area on Coram Experimental Forest in  western Montana, 55 percent was in standing green trees, 20 percent in  standing dead, and 25 percent in down material. In addition to tree  biomass, shrubs and herbs account for additional biomass (31). In terms of  weight, the average total biomass was 325 t/ha (145 tons/acre) with the  following distribution:

        Pct.      Standing green and dead 7.6 cm (3 in) diameter and  larger  49      Crown material less than 7.6 cm (3 in) diameter  12      Down wood 7.6 cm (3 in) diameter and larger  11      Down wood less than 7.6 cm (3 in) diameter  3      Shrubs and herbs  2      Litter  1      Duff  22