Volume 1: Conifers
Table of Contents
The Tree and Its Environment
General Notes and Selected References
Scientific Name Common Name
Abies Fir
Abies amabilis Pacific silver fir
Abies balsamea balsam fir
Abies concolor white fir
Abies fraseri Fraser fir
Abies grandis grand fir
Abies lasiocarpa subalpine fir
Abies magnifica California red fir
Abies procera noble fir
Chamaecyparis White-cedar
Chamaecyparis lawsoniana Port-Orford-cedar Chamaecyparis nootkatensis Alaska-cedar
Chamaecyparis thyoides Atlantic white-cedar
Juniperus Juniper
Juniperus occidentalis western juniper
Juniperus scopulorum Rocky Mountain juniper
Juniperus silicicola southern redcedar
Juniperus virginiana eastern redcedar
Larix Larch
Larix laricina tamarack
Larix lyallii alpine larch
Larix occidentalis western larch
Libocedrus Incense-cedar
Libocedrus decurrens incense-cedar
Picea Spruce
Picea breweriana Brewer spruce
Picea engelmannii Engelmann spruce
Picea glauca white spruce
Picea mariana black spruce
Picea pungens blue spruce
Picea rubens red spruce
Picea sitchensis Sitka spruce
Pinus Pine
Pinus albicaulis whitebark pine
Pinus banksiana jack pine
Pinus clausa sand pine
Pinus contorta lodgepole pine
Pinus echinata shortleaf pine
Pinus edulis pinyon
Pinus elliottii slash pine
Pinus flexilis limber pine
Pinus glabra spruce pine
Pinus jeffreyi Jeffrey pine
Pinus lambertiana sugar pine
Pinus monophylla singleleaf pinyon
Pinus monticola western white pine
Pinus nigra European black pine
Pinus palustris longleaf pine
Pinus ponderosa ponderosa pine
Pinus pungens Table Mountain pine
Pinus radiata Monterey pine
Pinus resinosa red pine
Pinus rigida pitch pine
Pinus sabiniana Digger pine
Pinus serotina pond pine
Pinus strobus eastern white pine
Pinus sylvestris Scotch pine
Pinus taeda loblolly pine
Pinus virginiana Virginia pine
Pseudotsuga Douglas-fir
Pseudotsuga macrocarpa bigcone Douglas-fir
Pseudotsuga menziesii Douglas-fir
Sequoia Redwood
Sequoia sempervirens redwood
Sequoiadendron Giant sequoia
Sequoiadendron giganteum giant sequoia
Taxodium Baldcypress
Taxodium distichum var. distichum baldcypress (typical) Taxodium distichum var. nutans pondcypress
Taxus Yew
Taxus brevifolia Pacific yew
Thuja Cedar
Thuja occidentalis northern white-cedar
Thuja plicata western redcedar
Torreya Torreya
Torreya taxifolia Florida torreya
Tsuga Hemlock
Tsuga canadensis eastern hemlock
Tsuga heterophylla western hemlock
Tsuga mertensiana mountain hemlock
Glossary
Summary of Tree Characteristics Checklist of Insects and Mites
Checklist of Organisms Causing Tree Diseases
Checklist of Birds Checklist of Mammals
Index of Authors and Tree Species
Abies amabilis Dougl. ex Forbes
Pacific Silver Fir
Pinaceae -- Pine family
Peggy D. Crawford and Chadwick Dearing Oliver
Pacific silver fir (Abies amabilis), also known as silver fir and Cascades fir, has a gray trunk, a rigid, symmetrical crown, and lateral branches perpendicular to the stem. It contrasts strikingly with the more limber crowns, acute branch angles, and generally darker trunks of its common associates Douglas-fir (Pseudotsuga menziesii), western hemlock (Tsuga heterophylla), and mountain hemlock (T. mertensiana). The species name, amabilis, means lovely.
Habitat
Native Range
Pacific silver fir is found in southeastern Alaska, in coastal British Columbia and Vancouver Island, and along the western and upper eastern slopes of the Cascade Range in Washington and Oregon. It also grows throughout the Olympic Mountains and sporadically in the Coast Ranges of Washington and northern Oregon. Near Crater Lake, OR, Pacific silver fir disappears from the Cascade Range and then reappears at a few locations in the Klamath Mountains of northwestern California. The major portion of its range lies
between latitudes 43° and 55° N. (35).
- The native range of Pacific silver fir.
Climate
Climate throughout the range of Pacific silver fir is distinctly maritime. Summers are cool, with mean daily temperatures of 13°
to 16° C (55° to 61° F), and winter temperatures are seldom lower than -9° C (16° F) (35). Mean number of frost-free days ranges from 40 near tree line to more than 250 at low elevations (26).
Length of growing season also differs from year to year at a given location. Mean annual precipitation varies greatly, ranging from 6650 mm (262 in) on the west coast of Vancouver Island to an extreme low of 965 mm (38 in) on the eastern side of Vancouver Island. Average annual precipitation in the Cascade Range is more than 1500 mm (59 in); winter snowpacks are as much as 7.6 m (25 ft) deep (9). A summer dry season is characteristic of this region, but Pacific silver fir is dependent on adequate soil moisture during the growing season. It is most abundant on sites where summer drought is minimal, such as areas of heavy rainfall, seepage, or prolonged snowmelt.
Soils and Topography
Pacific silver fir grows on soils developed from nearly every type of parent material found in the Northwest. Layering in soil profiles caused by successive deposits of volcanic ejecta, colluvium, or glacial till is especially common (1,43). The greatest known growth rates for Pacific silver fir occur at low elevations on fine- textured residual soils from sedimentary and basaltic rocks (16).
Growth is reduced on poorly drained or shallow rocky soils.
In northern Washington and British Columbia, podzolization is the dominant process in well-drained soils under Pacific silver fir. A typical podzol is characterized by strong acidity of organic (pH 3.3 to 4.0) and mineral horizons, moderate to thick (3 to 45 cm; 1 to 18 in) surface accumulations of organic matter, and moderate to extremely low base saturation. In Oregon, podzolization is less strongly expressed and soils are more shallow and rocky. Pacific silver fir has been found on many soil suborders throughout its range: Folists in the order Histosols; Aquents, Fluvents, Orthents in the order Entisols; Andepts, Aquepts, Ochrepts, Umbrepts in the order Inceptisols; and Aquods, Humods, and Orthods in the order Spodosols (35).
At upper elevations in Washington, soils beneath Pacific silver fir stands are generally low in available nitrogen, with availability decreasing with age (44). External nutrient cycling is slow; a mean nitrogen residence time as long as 120 years has been found in old- growth forest floors (24). Nitrification has not been found to occur.
Availability of phosphorus tends to be low but availability of base elements does not appear to limit plant growth (42). Internal cycling meets much of the annual nutrient requirements. Foliar nitrogen concentrations between 0.7 and 1.2 percent and foliar
phosphorus concentrations of 0.11 to 0.20 percent have been reported (3,42,52). Pacific silver fir differs significantly from western hemlock in its ability to accumulate specific elements (46).
Pacific silver fir grows at sea level along the coast from Alaska to the Olympic Peninsula; farther inland, it is absent at lower
elevations. Its range in elevation is narrowest in Alaska, 0 to 300 m (0 to 1,000 ft), and greatest in the western Cascade Range of Washington, where Pacific silver fir may be found from 240 to 1830 m (800 to 6,000 ft). In British Columbia it is found from 0 to 1525 m (0 to 5,000 ft) in elevation on western Vancouver Island and from 180 to more than 1680 m (600 to more than 5,500 ft) on the lower mainland. Pacific silver fir grows on the highest ridges and peaks in the Coast Ranges of Washington, from 365 to 850 m (1,200 to 2,800 ft). In the Olympic Mountains, it is the
predominant montane species up to 1400 m (4,600 ft), with lower limits at sea level on the west side and at 360 m (1,200 ft) in the central mountains. It is found between 610 and 1830 m (2,000 and 6,000 ft) in the Cascade Range in Oregon as far south as the divide between the Rogue and Umpqua Rivers. On the east side of the Cascade Range, it is confined to high elevations, down to 1160 m (3,800 ft) in Oregon and 1000 m (3,300 ft) in Washington (30,35).
Associated Forest Cover
Western hemlock is a common associate throughout most of the range of Pacific silver fir, in the Abies amabilis zone and portions of the Tsuga heterophylla zone (9). Noble fir (Abies procera) is an important associate in southern Washington and northern Oregon.
Other associates west of the Cascade Range are Douglas-fir, western redcedar (Thuja plicata), and grand fir (Abies grandis), with Sitka spruce (Picea sitchensis) and lodgepole pine (Pinus contorta) important near the coast. At subalpine elevations in the Tsuga mertensiana zone (9), Pacific silver fir is associated with mountain hemlock, Alaska-cedar (Chamaecyparis nootkatensis), and subalpine fir (Abies lasiocarpa). Toward the eastern limits of its range, it grows with a mixture of coastal and interior species:
western larch (Larix occidentalis), western white pine (Pinus monticola), lodgepole pine, subalpine fir, grand fir, and Engelmann spruce (Picea engelmannii). Shasta red fir (Abies magnifica var. shastensis) is an associate in the extreme southern portion of its range. Extensive pure stands of Pacific silver fir have been reported in the Mount Baker and Mount Rainier regions and elsewhere in the southern Washington Cascade Range (40).
Pacific silver fir is a major species in the forest cover type Coastal True Fir-Hemlock (Society of American Foresters Type 226) (5).
It is also found in the following types:
205 Mountain Hemlock
206 Engelmann Spruce-Subalpine Fir 223 Sitka Spruce
224 Western Hemlock
225 Western Hemlock-Sitka Spruce 227 Western Redcedar-Western Hemlock 228 Western Redcedar
229 Pacific Douglas-Fir
230 Douglas-Fir-Western Hemlock
Shrubs associated with Pacific silver fir are primarily ericaceous.
Blueleaf huckleberry (Vaccinium deliciosum), Cascades azalea (Rhododendron albiflorum), and rustyleaf menziesia (Menziesia ferruginea) are common understory species at higher elevations;
copper bush (Cladothamnus pyrolaeflorus) is important in subalpine British Columbia (2). Alaska huckleberry (Vaccinium alaskaense), big huckleberry (V. membranaceum), ovalleaf huckleberry (V. ovalifolium), and devilsclub (Oplopanax horridum) are widespread associates. At its lower limits of
elevation, Pacific silver fir is found with salal (Gaultheria shallon) and Oregongrape (Berberis nervosa).
Common herbaceous associates are common beargrass
(Xerophyllum tenax), bunchberry (Cornus canadensis), twinflower (Linnaea borealis), queenscup (Clintonia uniflora), dwarf
blackberry (Rubus lasiococcus), strawberryleaf blackberry (R.
pedatus), rosy twistedstalk (Streptopus roseus), coolwort
foamflower (Tiarella unifoliata), and deerfern (Blechnum spicant).
Rhytidiopis robusta is a constant bryophyte associate.
Major habitat types include Abies amabilis-Tsuga mertensiana/
Vaccinium membranaceum-Rhododendron albiflorum on cold, wet sites at high elevations and Abies amabilis/Xerophyllum tenax on shallow coarse-textured soils at various elevations. Abies
amabilis / Vaccinium alaskaense is a widespread type on modal sites. Abies amabilis/Rubus lasiococcus, Abies amabilis/Streptopus roseus, Abies amabilis / Tiarella unifoliata, and Tsuga
heterophylla-Abies amabilis/Blechnum spicant are herb-dominated types found in moist habitats. The Abies amabilis / Oplopanax
horridum type occupies wet, alluvial habitats (2,9).
Life History
Reproduction and Early Growth
Flowering and Fruiting- Pacific silver fir is monoecious; self- fertilization is possible because times of pollen dispersal and seed cone receptivity overlap on the same tree. Flowers differentiate from axillary buds of current-year lateral shoots in early July of the year before seed development (32). When receptive to
pollination, the seed cones appear purple, erect, and 8 to 16 cm (3 to 6 in) tall on the upper surfaces of 1-year-old branches in the upper parts of tree crowns. Just before pollination, the pollen cones appear red, pendent, and usually abundant on the lower surfaces of the branches somewhat lower on the crowns than the seed cones.
Cone buds burst the following May, and pollination occurs about 2 weeks later-before vegetative bud burst. The pollen does not
germinate and begin forming its pollen tube until 4 to 5 weeks later, resulting in a 6-week delay between pollination and fertilization (7,33).
Initiation of phenological events varies with latitude, altitude, aspect, weather, and snowpack and is apparently related to mean soil and air temperatures. For example, pollination may occur in mid-May at 900 in (2,960 ft) in central Washington but is delayed until mid-June at 1600 in (5,250 ft) and until late May in southern British Columbia (7,32,33).
Seeds are fully mature in late August, and dissemination begins in mid-September- one of the earliest dispersal times for Pacific Northwest conifers. Initiation of dispersal is apparently
independent of altitude or latitude (7); most seeds are shed by the end of October but may be shed until the following April (21,33).
Seed Production and Dissemination- Cone production begins at years 20 to 30 (33,37). Good seed years vary from region to region; a good seed crop generally occurs every 3 years (8).
Pacific silver fir is not considered a good seed producer; this condition is attributed to frequent years of low pollen, the extended period between pollination and fertilization, and archegonial abortion producing empty seeds (33). Percentage of sound seed varies, with reports of 6.7 to 35 percent and 51 percent
in one location (4). Germinative capacity varies widely from 3 to 70 percent- but averages 20 to 30 percent. Cleaned seeds range from 17,200 to 45,860/kg (7,800 to 20,800/lb) (37).
The seeds are heavier than seeds of most Pacific Northwest conifers except noble fir. Seeds each contain a single wing but often fall from the upright cone axis by pairs on ovuliferous scales, as the bracts contort and tear themselves from the cone-a process that does not require wind. When the seeds are dispersed by the wind, they do not carry far; unsound seeds are carried farther than sound seeds. In one study, only 9 percent of the sound seeds were found more than 114 in (375 ft) from the stand edge, compared with 41 percent at the stand edge and 34 percent more than 38 m (125 ft) (4).
Seedling Development- Pacific silver fir germinates in the spring after overwintering under snow. Germination is epigeal (37).
Seedlings germinating on snow because of early snowfall or late seed fall are generally short lived. Germination can occur on a variety of media: on litter humps and in moist depressions in the subalpine zone; on edges of melting snowpack in subalpine meadows; and in litter, rotten wood, moss, organic soils, mineral soils, and fresh volcanic tephra (2,11,25). Survival is better on mineral seedbeds than on organic seedbeds. Early mortality of seedlings is attributable more to germination on snow, adverse climatic effects, and competing vegetation than to disease (18).
Cool, moist habitats are best for germination, but full sunlight produces maximum subsequent growth. Seedlings can also grow under dense shade; seedlings 8 to 12 years old and about 10 cm (4 in) tall can frequently be found beneath older, closed forest
canopies. Seedlings that survive continue to grow very slowly, existing as advance regeneration that can be 65 to 110 years old and only 45 to 200 cm tall (18 to 80 in). When existing as advance regeneration, Pacific silver fir has flat-topped crowns caused by slow height growth relative to lateral branch growth.
Seedlings are sturdy and erect and resist being flattened by litter and heavy, wet snow. Survival of Pacific silver fir as advance regeneration at middle elevations, where western hemlock is primarily found in openings, is attributed partly to its ability to resist being buried by litter after snowmelt (40). At the highest elevations, Pacific silver fir is found primarily in openings and less frequently beneath the canopy (38). Stems of seedlings growing on
slopes often have a "pistol-butted" sweep, caused by heavy snow creeping downhill.
Vegetative Reproduction- Although Pacific silver fir can produce epicormic or adventitious sprouts, it does not regenerate by stump sprouting. Upturning of lower branches after tops of young trees are cut may resemble sprouting.
Sapling and Pole Stages to Maturity
Growth and Yield- There is a broad range of height growth rates of Pacific silver fir because of the wide variation of climates with elevation and latitude. Site index values (at 100 years) in southern British Columbia range from 12 to 46 m (40 to 150 ft) (26) and have been negatively correlated with elevation in Washington (16). In subalpine tree clumps at higher elevations, Pacific silver firs reach heights of 18 to 24 m (60 to 80 ft).
The largest Pacific silver fir tree known was in the Olympic National Park, WA. It was 256 cm (101 in) in d.b.h. and 74.7 m (245 ft) tall. Trees 55 to 61 m (180 to 200 ft) tall and more than 60 cm (24 in) in d.b.h. are common in old-growth stands. Trees 500 to 550 years old have been found on Vancouver Island and in the North Cascades National Park, WA. Maximum age reported is 590 years (48).
Early height growth from seeds is generally considered very slow;
9 or more years are usually required to reach breast height.
Juvenile height growth ranges from 10 to 40 cm (4 to 16 in) per year, depending on length of the growing season (50). Planted seedlings also grow slowly, with height increments of 3 to 15 cm (I to 6 in) for the first few years after planting (47). On productive sites at low elevations, Pacific silver fir is capable of much greater rates, averaging 90 cm (35 in) per year above breast height on some 30-year-old trees (16). Growth of released advance
regeneration is more rapid than early growth from seeds (20,49).
After an initial lag following overstory removal (as by avalanche, windstorm, or clearcutting), growth rates of 50 cm (20 in) or more per year can occur (49). When released from suppression, advance regeneration trees change from flat-topped to more conical crowns (41).
Pacific silver fir occasionally shows an abnormal height growth pattern, in which various sapling and pole-size trees curtail height
growth for at least 1 year while adjacent trees grow normally.
Causes of this phenomenon are not known.
Height-age and site index curves for Pacific silver fir have recently been constructed (23); however, little information on yield of second-growth stands is available. Data from sample plots on a variety of sites (table 1) indicate that large volumes can be expected from Pacific silver fir in pure stands or mixed with hemlocks. Close spacing and lack of taper are partly responsible for high volumes found in pure, even-aged stands of Pacific silver fir.
Table 1-Volume yield of second-growth stands in Washington and British Columbia, dominated by Pacific silver fir, based on sample plot data.
Plot location and
elevation
Proportion of Pacific
silver fir¹ Age Density Volume
pct yr trees/
ha m³/ha Washington:
King County, 975 m
100 47 1,850 980
Whatcom County, 760 m
95 70 2,879 875
Vancouver Island, BC (28):
Santa Maria
Lake, 533 m 85 100 1,361 1593
Labor Day
Lake, 922 m 65 125 1,016 1505
Haley Lake,
1204 m 64 108 1,011 950
Haley Lake,
1119 m 59 92 1,302 1197
Sarah Lake,
116 m 53 111 420 1220
pct yr trees/
acre ft³/acre Washington:
King County, 3,200 ft
100 47 749 14,004
Whatcom County, 2,500 ft
95 70 1,165 12,504
Vancouver Island, BC (28):
Santa Maria
Lake, 1,750 ft 85 100 551 22,764
Labor Day
Lake, 3,025 ft 65 125 411 21,506
Haley Lake,
3,950 ft 64 108 409 13,576
Haley Lake,
3,670 ft 59 92 527 17,105
Sarah Lake,
380 ft 53 111 170 17,434
¹Based on the total nymber of trees in sample plots.
Volume in old-growth stands is extremely variable, depending on the mix of species and degree of stand deterioration. One densely stocked plot at 1100 m (3,600 ft) in the north Cascades had 1813 m³/ha (25,895 ft³/acre), 83 percent Pacific silver fir by volume. An older, more open stand in the same area had 840 m³/ha (12,000 ft³/
acre).
Stands at upper elevations (predominantly Pacific silver fir) in western Washington carry large amounts of leaf biomass- 18 to 25 t/ha (8 to 11 tons/acre); total standing biomass ranges up to 500 t/
ha (223 tons/acre) in mature and older forests. Leaf area indexes of 14 have been reported (14). A large proportion of the net primary production is below ground in subalpine stands; this is apparently a characteristic of the cool sites and low nutrient mobilization rates
rather than the species itself. Values of net primary production in two upper elevation Pacific silver fir stands in western Washington were determined (15). In the 23-year-old stand, total net primary production was 18 000 kg/ha (16,060 lb/acre); in the 180-year-old stand it was 17 000 kg/ha (15,170 lb/acre). Of this, the above- ground portion was 6500 kg/ha (5,800 lb/acre) and 4500 kg/ha (4,010 lb/acre) for the two stands, respectively. Woody growth made up 65 percent of this amount in the younger stand, and 50 percent in the older stand. The below-ground portion was 11 500 kg/ha (10,260 lb/acre) and 12 500 kg/ha (11,150 lb/acre) for the two stands, respectively. Small conifer roots and mycorrhizae made up 65 percent of this amount in the younger stand and 73 percent in the older stand.
Rooting Habit- Pacific silver fir seedlings have roots that more closely resemble a true taproot system than do western hemlock seedlings (38), and the roots can penetrate more compact soils than can the roots of western redcedar, Sitka spruce, and western
hemlock (27). Seedlings can develop adventitious roots where volcanic tephra covers the original soil surface (1). Advance regeneration has, small root-to-shoot ratios, and the roots are predominantly in the organic layers. Mature Pacific silver fir can have a relatively flat, shallow, platelike root system on poorly drained or shallow soils or in areas where there is nutrient immobilization in the forest floor (15). On soils where
podzolization develops and organic matter accumulates, feeding roots become concentrated in organic horizons as a stand ages.
Peak growth of seedling roots occurs when shoots are least active.
Activity is high in early spring and late autumn even in cold soils.
Roots can also be active during the winter when soil temperatures are just above freezing; however, water conductance is
dramatically reduced after seedlings are preconditioned to cold temperatures (39). At upper elevations in both young and mature stands, a large proportion of annual biomass production is in the root systems (15). Roots are intensely mycorrhizal at upper elevations, and Cenococcum graniforme is a major mycorrhizal symbiont (45).
Reaction to Competition- Pacific silver fir can grow in a variety of stand development conditions. It can seed onto outwash after glacial retreat (35), seed into burned areas, develop from advance regeneration after removal of the overstory, and grow slowly from a suppressed tree into an overstory tree in more uneven-aged
stands where disturbances are minor.
Advance regeneration may have a cone-shaped crown or can become flat topped, with lateral branch growth greatly exceeding height growth. After extensive removal of the overstory, some (but not all) advance regeneration can accelerate in diameter and height growth and form a new forest (20).
Even-aged, pure, or mixed stands vary in stocking but can have more than 2,470 stems per hectare (1,000/acre). When crowns close during the sapling and pole stages, understory vegetation is almost completely eliminated by shade, causing an open forest floor. Lower limbs become shaded and die, creating branchfree boles. This condition may last 200 years (31).
Eventually the overstory crowns abrade and let more light into the understory, allowing development of shrubs and advance
regeneration. This may occur after one to three centuries-probably depending on site quality, spacing, and disturbance history-and has been observed to last to age 500 years (31). Individual overstory trees eventually die and advance regeneration grows slowly upward, creating a multi-aged, old-growth forest with a major component of Pacific silver fir that will be self-perpetuating, barring a major disturbance. Pacific silver fir is referred to as the climax species at mid-elevations of its range (9) because of its ability to survive in the shade and to emerge in all-aged stands.
Because of its slow early height growth, associated species such as western hemlock, Douglas-fir, and noble fir initially overtop
Pacific silver fir when grown in the open. After the initial overtopping, on many sites Pacific silver fir appears to outgrow and become taller than western hemlock after 100 years (19). On cool, moist sites at the upper extremes of the range of Douglas-fir, Pacific silver fir can stratify above Douglas-fir as well (40). Noble fir appears to maintain a height advantage over Pacific silver fir indefinitely on all sites where both species grow.
Pacific silver fir is one of the most shade-tolerant trees in the Northwest. There is confusion regarding its relative shade
tolerance compared with western hemlock. It has been described as equal, greater, and less shade tolerant than hemlock (26,40). It can most accurately be classed as very tolerant of shade.
Most silvicultural treatments of Pacific silver fir have dealt with
regeneration and early stocking levels after old-growth stands were logged. Regeneration practices vary from clearcutting followed by burning and planting to clearcutting with reliance on natural
advance and postlogging regeneration. Each practice successfully obtains regeneration for certain sites and management regimes.
Early stocking control-thinning sapling and pole-size trees to 495 to 740/ha (200 to 300/acre)- is practiced to increase growth rates of individual trees. Trees left in pole-size stands after thinning markedly increase in diameter growth and apparently respond to fertilization. Possible commercial thinning regimes, rotation ages, and regeneration plans for managed stands (where advance
regeneration may not be prevalent) are primarily in the planning stages.
Young, post-harvest stands can develop densely from advance regeneration. These stands may require thinning to maintain diameter growth, to keep from buckling in heavy snow or wind, and to ensure advance regeneration before the next harvest.
Damaging Agents- Pacific silver fir is easily killed by fire because of its shallow rooting habit and thin bark. It has lower resistance to windthrow than Douglas-fir, western hemlock, or western redcedar. It is susceptible to windthrow after heavy partial cuts (9), on the borders of clearcuts or partial cuts, and even in closed canopy stands during strong winds. Resistance to breakage from snow and damage by frost is moderate. The foliage of Abies amabilis and other true firs is more easily damaged by volcanic tephra than is the foliage of associated conifers (22). Several types of animal damage have been reported: heavy browsing by
Roosevelt elk (34), bark stripping by bears in pole-size stands, clipping of terminal buds by grouse and rodents (13), and cutting of cones and cone buds by squirrels.
Pacific silver fir is susceptible to many types of insect damage.
Seed chalcids (Megastigmus pinus and M. lasiocarpae) and cone maggots (Earomyia abietum) have been known to infest a high proportion of cones during good seed years (17). Western hemlock looper (Lambdina fiscellaria lugubrosa) and western blackheaded budworm (Acleris gloverana) are serious defoliators of mixed Pacific silver fir and western hemlock stands in British Columbia.
Many other loopers are of minor importance; two species that cause periodic outbreaks the greenstriped forest looper
(Melanolophia imitata) and saddleback looper (Ectropis crepuscularia). The western spruce budworm (Choristoneura
occidentalis) also feeds on Pacific silver fir in pure and mixed stands.
The silver fir beetle (Pseudohylesinus sericeus) and fir root bark beetle (P. granulatus) can be very destructive together and in combination with the root rotting fungi Armillaria mellea, Heterobasidion annosum, Phellinus weiri, and Poria subacida.
The last major outbreak of silver fir beetles lasted from 1947 to 1955; it killed 2.5 million m³ (88 million ft³) of timber in
Washington (12).
An imported pest, the balsam woolly adelgid (Adelges piceae), is the most devastating killer of Pacific silver fir. Attacks on the crown by this insect result in swelling or "gouting" of branch nodes, loss of needles, and reduced growth for many years; attacks on the stem usually cause a tree to die within 3 years. Trees of all ages and vigor are susceptible, although some individuals seem to have natural resistance. In southern Washington, damage has been heavy on high-quality sites at low elevations, such as benches and valley bottoms (28). In British Columbia, heaviest damage is on similar sites below 610 in (2,000 ft). Pacific silver firs growing with subalpine firs at high elevations are relatively immune and suffer only temporary gouting. Spread of the aphid has been slow since the major outbreak of 1950-57, but infested areas remain a problem. No effective direct control methods have been found for forest stands.
Pacific silver fir is a secondary host for hemlock dwarf mistletoe (Arceuthobium tsugense) and can be infected in mixed stands containing western or mountain hemlock. A. abietinum also attacks Pacific silver fir and western hemlock; it is more common in
central Oregon in the Cascade Range. Needle casts
(Lophodermium uncinatum, Phaeocryptopus nudus, Virgella robusta) and rusts (Uredinopsis spp.) are common on reproduction in some localities in British Columbia.
Thinning studies on the west coast of Vancouver Island indicated that Pacific silver fir is more susceptible to Heterobasidion
annosum root and butt rots than are western hemlock, Douglas-fir, or Sitka spruce. Airborne infection of Pacific silver fir stumps was not seasonal as in other species, and infection rates were high throughout the year (29). Pacific silver fir is also one of the Northwest conifers most susceptible to laminated root rot (Phellinus weiri) (27) and shoestring rot (Armillaria mellea).
Overmature Pacific silver firs are highly prone to heart rot, primarily by the Indian paint fungus (Echinodontium tinctorium) and the bleeding conk fungus (Haematostereum sanguinolentum).
In British Columbia, Pacific silver firs were free of decay to age 75; then incidence increased with age to 11 percent at 275 years, 40 percent at 375 years, and 100 percent in trees more than 400 years (6). Released advance regeneration scarred by logging is rarely infected by heart rot fungi. In one instance, E. tinctorium was nearly absent in young stands 30 years after release, even though adjacent unlogged stands were heavily infected. Lack of suitable branch stubs for entry by fungi and rapid closing of wounds because of accelerated growth are believed to prevent infection (20).
Deterioration is rapid after logging, windthrow, or death caused by insects or diseases. Within 5 years of death, loss in cubic volume can be from 50 to 100 percent. Primary decay fungi on dead wood are Fomitopsis pinicola, Ganoderma applanatum, Hirschioporus abietinus, and Poria subacida.
Special Uses
Pacific silver fir is marketed with western hemlock and is typically used for construction framing, subflooring, and sheathing. It is commonly used for construction plywood even though it is not as strong as Douglas-fir. Because of its light color and lack of odor, gum, and resin, Pacific silver fir is well suited for container veneer and plywood. It is occasionally used for interior finish and is suitable for poles. Good yields of strong pulp can be produced by both mechanical and chemical processes. It is a minor Christmas tree species, and its boughs are occasionally used for decorative greenery.
Because Pacific silver fir is common on midslopes of the Cascade Range, it is a large component of many municipal watersheds, wilderness areas, and recreation areas. Its beauty and ability to withstand or respond to human impact make it a suitable species for multiple-use management.
Genetics
Despite its extensive range, Pacific silver fir is not a highly
variable species. Cortical oleoresin analyses of sample trees from northern California to the Alaska border revealed no chemical variants, and variation among populations was similar to that within populations (51). Similar results were obtained from analyses of bark blister and leaf and twig oils.
No artificial hybrids of Pacific silver fir and any other species have been described. It does not hybridize with any of its true fir
associates even though pollen shedding and cone receptivity periods may overlap in some localities (7). Some morphological intermediates of Pacific silver fir and subalpine fir have been described, but these proved not to be hybrids (36).
The only known cultivated variety of Pacific silver fir is Abies amabilis var. compacta, a dwarf form that has current branches 2 to 3 cm (0.8 to 1.2 in) long.
Literature Cited
1. Antos, Joseph A., and Donald B. Zobel. 1986. Seedling establishment in forests affected by tephra from Mount St.
Helens. American Journal of Botany 73(4): 495-499.
2. Brooke, Robert C., E. B. Peterson, and V. J. Krajina. 1970.
The subalpine mountain hemlock zone. Ecology of Western North America 2(2):153-349.
3. Cameron, Ian Raymond. 1979. Foliar analysis of young amabilis fir: a comparison of well-grown and poorly grown trees. Thesis (B.S.), University of British Columbia,
Vancouver, BC. 25 p.
4. Carkin, Richard E., Jerry F. Franklin, Jack Booth, and Clark E. Smith. 1978. Seeding habits of upper-slope tree species. IV. Seed flight of noble fir and Pacific silver fir.
USDA Forest Service, Research Note PNW-312. Pacific Northwest Forest and Range Experiment Station, Portland, OR. 10 p.
5. Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Society of American Foresters, Washington, DC. 148 p.
6. Fowells, H. A., comp. 1965. Silvics of forest trees of the United States. U.S. Department of Agriculture, Agriculture Handbook 271. Washington, DC. 762 p.
7. Franklin, Jerry F., and Gary A. Ritchie. 1970. Phenology of cone and shoot development of noble fir and some
associated true firs. Forest Science 16(3):356-364.
8. Franklin, Jerry F., Richard Carkin, and Jack Booth. 1974.
Seeding habits of upper-slope tree species. 1. A 12-year record of cone production. USDA Forest Service, Research Note PNW-213. Pacific Northwest Forest and Range
Experiment Station, Portland, OR. 12 p.
9. Franklin, Jerry F., and C. T. Dyrness. 1973. Natural vegetation of Oregon and Washington. USDA Forest Service, General Technical Report PNW-8. Pacific
Northwest Forest and Range Experiment Station, Portland, OR. 417 p.
10. Franklin, Jerry F., and Francis R. Herman. 1973. True fir- mountain hemlock. In Silvicultural systems for the major forest types of the United States. p. 13-15. U.S. Department of Agriculture, Agriculture Handbook 445. Washington, DC.
11. Frenzen, Peter M., and Jerry F. Franklin. 1985.
Establishment of conifers from seed on tephra deposited by the 1980 eruptions of Mount St. Helens, Washington.
American Midland Naturalist 114:84-97.
12. Furniss, R. L., and V. M. Carolin. 1977. Western forest insects. U.S. Department of Agriculture, Miscellaneous Publication 1339. Washington, DC. 654 p.
13. Gessel, Stanley P., and Gordon H. Orions. 1967. Rodent damage to fertilized Pacific silver fir in western
Washington. Ecology 48:694-697.
14. Grier, C. C., and S. W. Running. 1977. Leaf area of mature northwestern coniferous forests: relation to site water balance. Ecology 58:893-899.
15. Grier, C. C., K. A. Vogt, M. R. Keyes, and R. L. Edmonds.
1981. Biomass distribution and above- and below-ground production in young and mature Abies amabilis ecosystems of the Washington Cascades. Canadian Journal of Forest Research 11:155-167.
16. Harrington, Constance A., and Marshall D. Murray. 1983.
Patterns of height growth in western true firs. In
Proceedings of the Biology and Management of True Fir in the Pacific Northwest Symposium. Contribution 45. p. 209- 214. C. D. Oliver and R. M. Kenady, eds. University of Washington College of Forest Resources, Institute of Forest Resources, Seattle.
17. Hedlin, A. F. 1974. Cone and seed insects of British Columbia. Environment Canada, Canadian Forestry Service, Information Report BC-X-90. Pacific Forest Research Centre, Victoria, BC. 63 p.
18. Hepting, George H. 1971. Diseases of forest and shade trees of the United States. U.S. Department of Agriculture, Agriculture Handbook 386. Washington, DC. 658 p.
19. Herman, Francis R. 1967. Growth comparisons of upper- slope conifers in the Cascade Range. Northwest Science 41 (l):51-52.
20. Herring, L. J., and D. E. Etheridge. 1976. Advance amabilis fir regeneration in the Vancouver Forest District. British Columbia Forest Service/Canadian Forestry Service, Joint Report 5. Pacific Forest Research Centre, Victoria, BC. 23 p.
21. Hetherington, J. C. 1965. The dissemination, germination and survival of seed on the west coast of Vancouver Island from western hemlock and associated species. British Columbia Forest Service, Research Note 39. Victoria, BC.
22 p.
22. Hinckley, Thomas M., Hiromi Imoto, Lee S. Lacker, Y.
Morikawa, K. A. Vogt, C. C. Grier, M. R. Keyes, R. 0.
Teskey, and V. Seymour. 1984. Impact of tephra deposition on growth in conifers: the year of the eruption. Canadian Journal of Forest Research 14:731-739.
23. Hoyer, Gerald E., and Francis R. Herman. 1989. Height- age and site index curves for Pacific silver fir in the Pacific Northwest. USDA Forest Service, Research Paper PNW- 418. Pacific Northwest Research Station, Portland, OR. 33 p.
24. Johnson, D. W., D. W. Cole, C. S. Bledsoe, K. Cromack, R.
L. Edmonds, S. P. Gessel, C. C. Grier, B. N. Richards, and K. A. Vogt. 1981. Nutrient cycling in forests of the Pacific Northwest. In Analysis of coniferous forest ecosystems in the Western United States. p. 186-232. R. L. Edmonds, ed.
Hutchinson and Ross, Stroudsburg, PA.
25. Kotar, John. 1972. Ecology of Abies amabilis in relation to its altitudinal distribution and in contrast to its common associate Tsuga heterophylla. Thesis (Ph.D.), University of Washington, Seattle. 171 p.
26. Krajina, V. J. 1969. Ecology of forest trees in British Columbia. Ecology of Western North America 2(l):1-146.
27. Minore, Don. 1979. Comparative autecological attributes of northwestern tree species: a literature review. USDA Forest Service, General Technical Report PNW-87. Pacific
Northwest Forest and Range Experiment Station, Portland, OR. 72 p.
28. Mitchell, R. G. 1966. Infestation characteristics of the
balsam woolly aphid. USDA Forest Service, Research Paper PNW-35. Pacific Northwest Forest and Range Experiment Station, Portland, OR. 18 p.
29. Morrison, D. J., and A. L. S. Johnson. 1970. Seasonal variation of stump infection by Fomes annosus in coastal British Columbia. Forestry Chronicle 46(3):200-202.
30. Murray, Marshall D., and Daniel L. Treat. 1980. Pacific silver fir in the Coast Range of southwestern Washington.
Northwest Science 54:119-120.
31. Oliver, Chadwick Dearing, A. B. Adams, and Robert J.
Zasoski. 1985. Disturbance patterns and forest development in a recently glaciated valley in the northwestern Cascade Range of Washington, U.S.A. Canadian Journal of Forest Research 15:221-232.
32. Owens, J. H., and M. Molder. 1977. Vegetative bud development and cone differentiation in Abies amabilis.
Canadian Journal of Botany 55:992-1009.
33. Owens, J. H., and M. Molder. 1977. Sexual reproduction of Abies amabilis. Canadian Journal of Botany 55:2253-2667.
34. Packee, Edmond Charles. 1976. An ecological approach toward yield optimization through species allocation.
Thesis (Ph.D.), University of Minnesota, St. Paul. 740 p.
35. Packee, E. C., C. D. Oliver, and P. D. Crawford. 1983.
Ecology of Pacific silver fir. In Proceedings of the biology and management of true fir in the Pacific Northwest
Symposium. Contribution 45. p. 19-34. C. D. Oliver and R.
M. Kenady, eds. University of Washington College of Forest Resources, Institute of Forest Resources, Seattle.
36. Parker, W. H., G. E. Bradfield, J. Maza, and S.-C. Liu.
1979. Analysis of variation in leaf and twig characteristics of Abies lasiocarpa and Abies amabilis from north-coastal British Columbia. Canadian Journal of Botany 57:1354- 1366.
37. Schopmeyer, C. S., tech. coord. 1974. Seeds of woody plants in the United States. U.S. Department of Agriculture, Agriculture Handbook 450. Washington, DC. 883 p.
38. Scott, D. R. M., J. N. Long, and J. Kotar. 1976.
Comparative ecological behavior of western hemlock in the Washington Cascades. In Proceedings, western hemlock management conference. Contribution 34. p. 26-33.
William A. Atkinson and Robert J. Zasoski, eds. University of Washington, College of Forest Resources, Institute of Forest Resources, Seattle. 317 p.
39. Teskey, Robert 0., Thomas M. Hinckley, and Charles C.
Grier. 1984. Temperature-induced change in the water relations of Abies amabilis (Dougl.) Forbes. Plant Physiology 74: 77-80.
40. Thornburgh, Dale Alden. 1969. Dynamics of the true fir- hemlock forests of the west slope of the Washington
Cascade Range. Thesis (Ph.D.), University of Washington, Seattle. 210 p.
41. Tucker, Gabriel F., Thomas M. Hinckley, Jerry Leverenz, and Shimei Jiang. 1987. Adjustment to foliar morphology in the acclimation of understory Pacific silver fir following clear cutting. Forest Ecology and Management 21:249-268.
42. Turner, J., and M. J. Singer. 1976. Nutrient distribution and cycling in a subalpine coniferous forest ecosystem. Journal of Applied Ecology 13:295-30 1.
43. Ugolini, K C., R. Minden, H. Dawson, and J. Zachara.
1977. An example of soil processes in the Abies amabilis zone of central Cascades, Washington. Soil Science 124 (5):291-302.
44. Vitousek, P., J. R. Gosz, C. C. Grier, J. M. Melillo, W. A.
Reiners, and R. L. Todd. 1979. Nitrate losses from disturbed ecosystems. Science 204:469-474.
45. Vogt, Kristiina A., Robert L. Edmonds, and Charles C.
Grier. 1981. Seasonal changes in biomass and vertical distribution of mycorrhizal and fibrous-textured conifer fine roots in 23 and 180-year old subalpine Abies amabilis stands. Canadian Journal of Forest Research 11:223-229.
46. Vogt, Kristiina A., R. Dahlgren, F. Ugolini, D. Zabowski, E. E. Moore, and R. J. Zasoski. 1987. Aluminum, Fe, Ca, Mg, K, Mn, Cu, Zn and P in above- and below-ground biomass. 1. Abies amabilis and Tsuga mertensiana.
Biogeochemistry 4:277-294.
47. Walters, J., and P. G. Haddock. 1966. Juvenile height
growth of eight coniferous species on five Douglas-fir sites.
University of British Columbia Faculty of Forestry, Research Paper 75. Vancouver. 16 p.
48. Waring, R. H., and J. F. Franklin. 1979. Evergreen coniferous forests of the Pacific Northwest. Science 204:1380-1386.
49. Williams, Carroll B., Jr. 1968. Juvenile height growth of four upper-slope conifers in Washington and northern Oregon Cascade Range. USDA Forest Service, Research Paper PNW-70. Pacific Northwest Forest and Range Experiment Station, Portland, OR. 13 p.
50. Williams, Carroll B., Jr. 1968. Seasonal height growth of
upper slope conifers. USDA Forest Service, Research Paper PNW-62. Pacific Northwest Forest and Range Experiment Station, Portland, OR. 7 p.
51. Zavarin, E., K. Snajberk, and W. B. Critchfield. 1979.
Monoterpene variability of Abies amabilis cortical oleoresin. Biochemical Systematics 1:87-93.
52. Zobel, Donald B., Arthur McKee, Glenn M. Hawk, and C.
T. Dyrness. 1976. Relationships of environment to
composition, structure, and diversity of forest communities of the central western Cascades of Oregon. Ecological Monographs 46:135-156.
Abies balsamea (L.) Mill.
Balsam Fir
Pinaceae -- Pine family Robert M. Frank
Balsam fir (Abies balsamea) is one of the more important conifers in the northern United States and in Canada. Within its range it may also be referred to as balsam, Canadian balsam, eastern fir, and bracted balsam fir. It is a small to medium-sized tree used primarily for pulp and light frame construction, and it is one of the most popular Christmas trees. Wildlife rely extensively on this tree for food and shelter.
Habitat
Native Range
In Canada, balsam fir extends from Newfoundland and Labrador west through the more northerly portions of Quebec and Ontario, in scattered stands through north-central Manitoba and
Saskatchewan to the Peace River Valley in northwestern Alberta, then south for approximately 640 km (400 mi) to central Alberta, and east and south to southern Manitoba.
In the United States, the range of balsam fir extends from extreme northern Minnesota west of Lake-of-the-Woods southeast to Iowa;
east to central Wisconsin and central Michigan into New York and central Pennsylvania; then northeastward from Connecticut to the other New England States. The species is also present locally in the mountains of Virginia and West Virginia (23,30).
Balsam fir grows from sea level to within 15 to 23 m (50 to 75 ft) below the 1917 m (6,288 ft) summit of Mount Washington in the White Mountains of New Hampshire. At this elevation prostrate balsam fir is found in sheltered areas (1).
- The native range of balsam fir.
Climate
Balsam fir grows best in the eastern part of its range in
southeastern Canada and the Northeastern United States. This area is characterized by cool temperatures and abundant moisture.
Growth is optimum in areas with a mean temperature of 2° to 4° C (35° to 40° F), a January average ranging from -18° to -12° C (0°
to 10° F), a July mean temperature ranging from 16° to 18° C (60°
to 65° F), and mean annual precipitation ranging from 760 to 1100 mm (30 to 43 in) (1).
The mean annual temperature within the range of balsam fir varies from -4° to 7° C (25° to 45° F). Mean annual precipitation records
show as much as 1400 mm (55 in) to as little as 390 mm (15 in).
The amount of growing season precipitation is from 150 to 620 mm (6 to 25 in) (1). There are 80 to 180 frost-free days and about 110 days for optimum growth (1).
Soils and Topography
Balsam fir grows on a wide range of inorganic and organic soils originating from glaciation and generally falling within the acid Spodosol, Inceptisol, and Histosol soil orders. These are
characterized by a thick mor humus and a well-defined A
2
horizon, usually gray in appearance because of leaching, and commonly caused by abundant rainfall, cool climate, and
coniferous cover. Many of the glacial till soils in New England are shallow and have a compact layer about 46 cm (18 in) below the surface (11).
Soil moisture was the most important predictor of site index in a study in Newfoundland. Soil nutrient status and topography, in that order, were of lesser importance. Glacial tills, often shallow, cover much of the area (27).
Balsam fir has been reported as growing on soils of a wide range of acidity. In the northern Lake States it is most common on cool, wet-mesic sites with pH values between 5.1 to 6.0 (19). Optimum growth occurs on soils where the pH of the upper organic layers is between 6.5 and 7.0 (1). On gravelly sands and in peat swamps, growth is comparatively slow (41).
Associated Forest Cover
Tree species associated with balsam fir in the boreal region of Canada are black spruce (Picea mariana), white spruce (Picea glauca), paper birch (Betula papyrifera), and quaking aspen (Populus tremuloides). In the more southerly northern forest region, additional associates include bigtooth aspen (Populus grandidentata), yellow birch (Betula alleghaniensis), American beech (Fagus grandifolia), red maple (Acer rubrum), sugar maple (Acer saccharum), eastern hemlock (Tsuga canadensis), eastern white pine (Pinus strobus), tamarack (Larix laricina), black ash (Fraxinus nigra), and northern white-cedar (Thuja occidentalis).
Red spruce (Picea rubens) is an important associate in New Brunswick and Maine. Occasional associates are balsam poplar
(Populus balsamifera), gray birch (Betula populifolia), red pine (Pinus resinosa), jack pine (Pinus banksiana), and American elm (Ulmus americana) (10).
Pure stands of balsam fir or stands in which balsam fir is the major component of growing stock make up the forest cover type
Balsam Fir (Society of American Foresters Type 5) (10). Balsam fir is also a major component in two other eastern forest cover types: Red Spruce-Balsam Fir (Type 33) and Paper Birch-Red Spruce-Balsam Fir (Type 35). It is an associated species in 22 eastern forest cover types and in 4 western forest cover types.
Common shrubs associated with balsam fir include beaked hazel (Corylus cornuta), mountain maple (Acer spicatum), Labrador-tea (Ledum groenlandicum), Canada yew (Taxus canadensis), red raspberry (Rubus idaeus var. strigosus), sheep-laurel (Kalmia angustifolia), and hobblebush (Viburnum lantanoides) (10,41).
Among the herbaceous plants commonly found under balsam fir are twinflower (Linnaea borealis), bunchberry (Cornus
canadensis), starflower (Trientalis borealis), creeping snowberry (Gaultheria hispidula), sedges (Carex spp.), common woodsorrel (Oxalis montana), bluebead lily or cornlily (Clintonia borealis), painted trillium (Trillium undulatum), cinnamon fern (Osmunda cinnamomea), sweetscented bedstraw (Galium triflorum), Canada mayflower (Maianthemum canadense), and spinulose woodfern (Dryopteris spinulosa).
Certain associations of shrubs, herbs, and mosses indicate forest site quality (41). The four main indicator associations, designated as Hylocomium/ Hypnum, Cornus/Maianthemum, Oxalis/Cornus, and Viburnum/Oxalis indicate, in the order listed, increasing productivity of site and increasing proportions of shrubs and hardwood trees in natural stands. Only the Hylocomium/Hypnum sites are likely to be occupied by pure balsam fir.
Life History
Reproduction and Early Growth
Flowering and Fruiting- Exposure to light influences flowering in balsam fir. In New Brunswick, female strobili were observed on 83 percent of dominant, 59 percent of codominant, and 6 percent
of intermediate trees. None were found on suppressed trees (41).
Balsam fir is monoecious. In spring, 1 year before pollination, male (staminate) and female (ovulate or pistillate) strobili differentiate from flower buds. The strobili are microscopically recognizable at this time. Male strobili usually are distinguishable before the female strobili because they initially develop more rapidly. Flower buds usually open in late May or early June before vegetative buds (41) but have been reported as flowering as early as late April (42).
Male strobili, yellowish-red and tinged with purple, develop in the axils of leaves along the undersides of the 1-year-old twigs,
usually in dense clusters. Their position in the crown is mostly within 5 m (15 ft) of the top and is almost always below the female strobili. Female strobili are purplish and are found singly or in small groups, confined to the top 1.5 m (5 ft) of the crown.
They are located on the upper side of the twig and, like the male strobili, develop on the previous year's twig. Flower production is best on the outer end of branches (41,42). At maturity, male flowers are about 3 mm (0.1 in) long; female flowers are about 25 mm (1.0 in) long (1).
Pollen grains are yellow; when developed, their average diameter is 90 µ (0.00354 in). In one series of observations in Ontario, fertilization occurred on June 25 (1). The mature fruit is an erect cone 5 to 10 cm (2 to 4 in) long with short, round, irregularly notched scales and pointed tips. There are thin, closely
overlapping fan-shaped scales near the center of the cone. The cone matures and ripens during the first fall in late August and early September. The scales and shorter bracts drop away with the seeds, leaving the central axis, which can persist for many years.
Seed Production and Dissemination- Regular seed production probably begins after 20 to 30 years. Cone development has been reported for trees 15 years of age and younger and only 2 m (6.6 ft) tall. Good seed crops occur at intervals of 2 to 4 years, with some seed production usually occurring during intervening years (1). On the average, 35 L (bushel) containing 1,000 to 2,000 cones weighs approximately 16 kg (35 lb) and yields 1000 to 1200 g (35 to 42 oz) of cleaned seeds. The number of cleaned seeds per
kilogram (2.2 lb) ranges from 66,000 to 208,000 and averages 131,000. These are about 134 seeds per cone (42). The seed yield of balsam fir ranged from 5.6 to 20.2 kg/ha (5 to 18 lb/acre) during
several good seed years in Ontario (1). Over a 37-year period, annual seed production in this area averaged 1,950 seeds per square meter (181/ft²) (15).
The period of balsam fir seedfall is long and dissemination
distances vary. Seedfall begins late in August, peaks in September and October, and continues into November. Some seeds fall
throughout the winter and into early spring. Most of the seeds are spread by wind-some to great distances over frozen snow-and some are spread by rodents. Although seeds may disseminate from 100 m (330 ft) to more than 160 m (525 ft), effective distances are 25 m to 60 m (80 to 200 ft) (1,11,28). Many seeds falling with the cone scales land close to the base of the tree.
Balsam fir seeds have dormant embryos and should be stratified in moist sand at about 50 C (410 F) for at least 30 days before
planting. Germination is epigeal (42).
Seedling Development- Within the range of suitable temperatures, moisture is more important than light for
germination. In fact, light intensities of only 10 percent of full sunlight result in successful germination (1). The low capacity of planted balsam fir seeds to germinate may be attributed in part to seed injury during the cleaning process. The age of the tree may also contribute to the viability of seeds.
A study in Michigan (41) showed that germination was highest for a 41-year-old tree (68 percent), varied for trees 30 years old (8 to 57 percent), and was lowest for trees 155 years old (10 percent).
Testing of 32 commercial seed lots showed average germination of about 26 percent with a range of 4 to 62 percent (42). Once the seed reaches the ground, its viability diminishes quickly and is gone within 1 year (13). It has been suggested, however, that in cold swamps viability of some seeds is retained for 2 to 3 years (1).
Most germination occurs from late May to early July. Survival the first winter is questionable if germination occurs after mid-July (1). If enough moisture is available, almost any seedbed type is satisfactory, but mineral soil-neither too sandy nor too heavy-with some shade is best. Litter and humus are poor seedbeds, especially if moisture is inadequate or -light is excessive. Competition, often severe, makes heavy sod the poorest seedbed (11).
A thick layer of duff exceeding about 8 cm (3 in) is less favorable
for balsam fir but even worse for the slower growing associated spruces. Balsam fir seedlings may have a heavy central root, much like a taproot, that extends to the bottom of the humus layer and then splits into several laterals. In general, balsam fir roots grow more rapidly and penetrate deeper than red spruce roots. Where seasonal root elongation of young balsam fir growing in humus averaged 10.6 cm (4.2 in), red spruce was 7.6 cm (3.0 in), and white spruce 9.0 cm (3.5 in), or 39 percent and 18 percent less, respectively (1).
Because the surface of thick duff usually dries out, there may be some delayed germination as late as August. Few seedlings
become established, however. The closer seeds lie to mineral soil, the greater the initial establishment of seedlings.
Seedlings starting in the open may sustain heavy mortality when surface temperatures exceed 46° to 54° C (115° to 130° F) or when there is drought or frost heaving. Seedlings may also be smothered or crushed by litter, ice, snow, and hardwood leaves.
Losses after the first year usually are minor. As seedlings develop, light at intensities of at least 50 percent of full sunlight are
necessary for optimum growth (11,41). Damage caused by late spring frost to new foliage of young seedlings is seldom severe.
Balsam fir seedlings about 15 cm (6 in) tall can be considered to be established (11), especially if secondary branching has
occurred. Early growth is then determined largely by the amount and character of dominant competition. Bracken, raspberry, and hardwood sprouts-especially the maples-are the chief competitors on heavily cutover lands in the Northeast. These species may increase dramatically when the original basal area is reduced by 50 percent or more and may dominate the site for 10 to 25 years (2). Unless there has been some soil disturbance, there will be little regeneration of balsam fir and spruce immediately following logging (45). Both balsam fir and the spruces can survive many years of suppression and still respond to release (11,41). The space required for the continual development and establishment of new seedlings probably exceeds that created by the removal of
individual trees. To ensure successful regeneration relatively small groups of trees should be removed initially (12).
Vegetative Reproduction- Layering is not an important means of regeneration except for prostrate balsam fir growing in the more northern and mountainous locations such as Isle Royale in Lake
Superior, and the White Mountains of New Hampshire. Layering also occurs in open swamps and deep mossy areas and under white pine and jack pine overstories. Trees of any age apparently may layer. Second generations, vegetatively produced, develop when connecting tissues decay and separate (1).
Balsam fir apparently grafts easily (41). In a study in New York, greenhouse grafts were 85 percent successful and field grafts were 80 percent successful. One attempt to air-layer balsam fir was unsuccessful (1). Balsam fir Christmas trees are stump cultured from lateral branches or adventitious shoots.
Sapling and Pole Stages to Maturity
Growth and Yield- Balsam fir at maturity is small to medium size, depending on location and growing conditions. In general, heights range from 12 to 18 m (40 to 60 ft); diameters range from 30 to 46 cm. (12 to 18 in) at breast height (41). Where growth is optimum, as in the Green River watershed in New Brunswick, some trees can reach 27 m (90 ft) in height and 75 cm. (30 in) in d.
b.h. The reported record d.b.h. for balsam fir is 86 cm (34 in).
Maximum age is about 200 years (1). How large or how fast balsam fir grows, or how much a stand of balsam fir will yield is related to site factors such as biotic, climatic, and soil conditions, and to age. The condition of the tree or stand and the composition and structure of the stand also influence growth.
Diameter growth was related to vigor and crown length-to-height ratio in a study in Maine. Balsam fir with high vigor and a ratio of at least 0.7- the proportion of live-crown length to total tree height averaged 6.1 cm (2.4 in) of growth in d.b.h. in 10 years. Less vigorous trees with smaller crown-length ratios ranged downward to an average of 1.0 cm (0.4 in) of growth in 10 years. Vigorous trees with room to grow attain a d.b.h. of at least 25 cm (10 in) in about 50 years (41). In uneven-aged stands of several density classes in Maine, balsam fir grew faster in diameter than spruce and hemlock (35).
Data obtained from stem analysis of balsam fir growing on sites of varying quality in northern Maine has shown height growth curves to be polymorphic (fig. 1). Height growth varies with site quality.
From these curves the average site index of a stand can be
estimated (16). Monomorphic or harmonized site index curves for balsam fir are also available (17).
Figure 1-Polymorphic site index curves (base age 50 years at breast height) for balsam fir in northern Maine, as derived from stem data (16).
Balsam fir is a strong contender for space in stands in which it grows. A 20-year record of stands containing balsam fir in the Penobscot Experimental Forest in Maine showed that the periodic annual volume ingrowth of the species, as a proportion of total volume ingrowth, greatly exceeded its representation in the original stands (12). Because of its many natural enemies,
however, volume mortality of balsam fir also greatly exceeds its original representation in these stands.
Balsam fir accounted for 35 percent of the average annual net growth in predominantly softwood stands and 32 percent in mixed stands that were extensively managed. These stands were growing at annual rates of 3.5 m³/ha (49.3 ft³/acre) and 2.9 m³/ha (41.1 ft³/
acre), respectively (31).
Yields in total cubic-foot volume, including stump and top, of all
trees larger than 1.5 cm (0.6 in), in d.b.h. are given in table 1.
These yields are based on sample plots in even-aged spruce-fir stands, mostly on old fields. They tend to exaggerate the yields that might be expected from the irregular stands that develop after harvesting (41).
Table 1- Total tree volume (exclusive of roots) of balsam fir greater than 1.5 cm (0.6 in) in d.b.h. by age and site index (41).
Site index¹
12.2 m or 40 ft
15.2 m or 50 ft
18.3 m or 60 ft
21.3 m or 70 ft Age
yr m³/ha
20 6 8 9 12
30 50 67 85 102
40 136 182 229 276
50 204 274 344 414
60 245 329 413 497
70 267 360 452 543
80 286 384 481 579
90 300 403 506 609
yr ft³/acre
20 80 110 135 165
30 720 960 1,210 1,455
40 1,940 2,600 3,270 3,940
50 2,190 3,920 4,920 5,910
60 3,500 4,700 5,900 7,100
70 3,820 5,140 6,450 7,760
80 4,080 5,480 6,870 8,270
90 4,290 5,760 7,230 8,700
¹Base age 50 years when age is measured at d.b.h.- total tree age is estimated to be 65 years at that time.
Simulating the management and growth of forest stands
containing balsam fir is possible because of advances in computer
technology. A matrix model, FIBER (36), has been developed for stands in the Northeast. Even-aged and multi-aged stands,
containing balsam fir, spruce, northern hardwoods, and other associated species, can be programmed to simulate a range of silvicultural treatments.
In a ranking with both hardwoods and softwoods from around the world, balsam fir is highest with a total above-ground ovendry biomass at age 50 of 184 t/ha (82 tons/acre). Annual increment or annual net primary production averages 10.3 t/ha (4.6 tons/acre) (20). In New Brunswick (3), dry-matter production of balsam fir in pure stands increased dramatically with increases in stand densities of from 1,730 stems per hectare (700/acre) to 12,350/ha (5,000/acre). At an average age from release of 43 years, total above-ground biomass was 96 t/ha (43 tons/acre) for the least dense stand and 143 t/ha (64 tons/acre) for the most dense stand.
Rooting Habit- Balsam fir root systems are mostly confined to the duff layer and to the upper few centimeters of mineral soil (11). Windfall potential is high. Damage from wind is especially likely when the shallow root systems are loosened by heavy rainfall and gusty winds and where timber removals from stands not previously thinned have been poorly conducted. These usually older, dense stands are susceptible probably because root
development has been poor.
Root penetration on deep or shallow soils extends to 60 to 75 cm (24 to 30 in) and has been reported to a depth of 137 cm (54 in) in sandy soils in northern Ontario. Lateral roots of balsam fir are usually strongly developed and extend horizontally in all directions to 1.5 m (5 ft) or more (1).
Root breakage and other root damage caused by swaying trees may not be as severe as is commonly thought. Most investigators agree, however, that some root breakage probably occurs because of frostheaving and swaying. During epidemics of spruce
budworm (Choristoneura fumiferana), rootlet mortality can reach 75 percent after 3 consecutive years of defoliation (1).
Balsam fir root grafts are probably common and have been
reported frequently. Abrasion of the bark of roots of swaying trees on lowland soils and interroot compatibility and growth pressure on upland soils apparently account for the majority of root grafts.
Infection may spread through grafted roots to damage other
balsam fir trees (1).
Reaction to Competition- Balsam fir has a strong ability to become established and grow under the shade of larger trees (7,11). It is classified as very tolerant. Because relative tolerance of species may vary with soil fertility, climate, and age, balsam fir is rated as both more and less shade tolerant than red spruce, and more tolerant than either black or white spruce (41). Intraspecific competition is evident in many sapling and small pole-size stands of pure balsam fir. As these stands mature, dominance usually is expressed. Competition is severe in dense fir thickets, however, and growth rates of individual trees suffer greatly. Other major competition is from the shade-tolerant hardwoods.
In New England, balsam fir is considered a subclimax type, except that it may be a climax species in the zone below timberline. It tends to become climax in Quebec and in the Lake States (41).
Damaging Agents- Many agents act to hinder the growth of balsam fir. Insects and diseases may be devastating. Flammable needles, often close to the ground, shallow root systems, and thin resinous bark make balsam fir susceptible to severe damage and mortality from fire. Susceptibility to wind damage is especially high in old unmanaged stands growing on wet shallow soils.
Various species of mice, voles, and birds consume balsam fir seed;
birds and squirrels nip buds; and black bears girdle mature trees.
Balsam fir has several insect enemies, the most important by far being the spruce budworm. Despite its name, the spruce budworm prefers fir over spruce; it is most likely to cause heavy damage and mortality in stands that contain mature fir, or that have a dense stocking of fir or a high proportion of fir in relation to other species. Vast budworm outbreaks in eastern North America, perhaps as many as 11 since 1704, have killed tens of millions of cubic meters (hundreds of millions of ft³) of balsam fir (6).
Defoliation causes extensive root mortality. Evidence of budworm attack such as deformation, buried leaders, and decay can be seen 40 or more years later (1). Detailed articles about this important insect pest, with suggestions to alleviate damage, have been written (7,32) and a comprehensive bibliography assembled (25).
A classification system for tree vigor and budworm resistance was developed as a guide for selecting spruce and fir trees to remove or retain so as to make spruce-fir stands less vulnerable to spruce
