Index of Species Information

SPECIES:  Picea mariana

Introductory

SPECIES: Picea mariana
AUTHORSHIP AND CITATION : Uchytil, Ronald J. 1991. Picea mariana. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ []. ABBREVIATION : PICMAR SYNONYMS : Picea mariana var. brevifolia (Peck) SCS PLANT CODE : PIMA COMMON NAMES : black spruce bog spruce swamp spruce shortleaf black spruce TAXONOMY : The genus Picea consists of about 30 species of evergreen trees found in cool, temperate regions of the northern hemisphere. Seven species of Picea, including black spruce, are native to North America. The currently accepted scientific name of black spruce is Picea mariana (Mill.) B.S.P. [41]. Natural hybridization between species of Picea is common. Natural hybrids between black and red spruce (P. rubens) are common where the ranges of these two species overlap in Nova Scotia, New Brunswick, and Quebec [65]. Although rare, natural hybrids between black and white spruce (P. glauca) have been found in Minnesota and other areas [65]. LIFE FORM : Tree, Shrub FEDERAL LEGAL STATUS : No special status OTHER STATUS : NO-ENTRY


DISTRIBUTION AND OCCURRENCE

SPECIES: Picea mariana
GENERAL DISTRIBUTION : Black spruce is a wide-ranging and abundant tree.  It is distributed transcontinentally across northern North America.  It grows from Newfoundland and northern Quebec, west across northern Canada to the west coast of Alaska, south to central British Columbia, south and east to central Minnesota, and east to Rhode Island and Massachusetts [41]. Black spruce occurs in isolated patches along the southern portion of its range in southern Wisconsin, southern Michigan, Pennsylvania, and New Jersey [65]. ECOSYSTEMS :    FRES10  White - red - jack pine    FRES11  Spruce - fir    FRES18  Maple - beech - birch    FRES19  Aspen - birch    FRES23  Fir - spruce STATES :      AK  CT  ME  MA  MI  MN  NH  NJ  NY  PA      RI  VT  WI  AB  BC  LB  MB  NB  NF  NT      NS  ON  PE  PQ  SK  YT BLM PHYSIOGRAPHIC REGIONS : NO-ENTRY KUCHLER PLANT ASSOCIATIONS :    K093  Great Lakes spruce - fir forest    K094  Conifer bog    K095  Great Lakes pine forest    K096  Northeastern spruce - fir forest SAF COVER TYPES :      1  Jack pine      5  Balsam fir     12  Black spruce     13  Black spruce - tamarack     16  Aspen     18  Paper birch     32  Red spruce     33  Red spruce - balsam fir     35  Paper birch - red spruce - balsam fir     37  Northern white cedar     38  Tamarack     39  Black ash - American elm - red maple    107  White spruce    201  White spruce    202  White spruce - paper birch    203  Balsam poplar    204  Black spruce    217  Aspen    251  White spruce - aspen    252  Paper birch    253  Black spruce - white spruce    254  Black spruce - paper birch SRM (RANGELAND) COVER TYPES : NO-ENTRY HABITAT TYPES AND PLANT COMMUNITIES : Climax black spruce forests are widespread across boreal North America. Six generalized climax types have been outlined [22].  These are:  (1)  Black spruce-feather moss - These are well-stocked to dense spruce stands with a well-developed carpet of feather mosses (Pleurozium schreberi, Hylocomium splendens, Ptilium crista-castrensis).  This type is most common at the southern and central portion of black spruce's range.  (2)  Black spruce-lichen - These are open woodlands with a well-developed carpet of reindeer lichens (Cladina spp.).  This type occurs along the northern portion of black spruce's range in the forest-tundra transition.  It remains an open woodland due to the unfavorable climate.  (3)  Black spruce-dwarf shrub - These are closed black spruce stands with a well-developed ericaceous dwarf shrub layer, and forest floor dominated by mosses and reindeer lichens.  This type occurs in the central and southern boreal forests.   (4)  Black spruce-sphagnum - this type is made up of open to closed pure black spruce stands on organic or wet mineral soils with well-developed ericaceous dwarf shrub cover and sphagnum mosses (Sphagnum spp.) dominating the forest floor.  This type occurs throughout the range of black spruce.  (5)  Black spruce-speckled alder (Alnus rugosa) - These are pure or mixed stands on areas where the water table is near the surface during the growing season.  Stands have well-developed tall shrub and herbaceous layers.  (6)  Black spruce-sedge - These are very open stands of stunted trees on wet sites with the ground dominated by sedges and grasses and well-developed moss layers (but little or no sphagnum mosses).  This type is widely distributed throughout boreal regions. Published classifications listing black spruce as an indicator or dominant part of the vegetation in community types (cts) or ecosystem associations (eas) are presented below: Area                        Classification     Authority AK                          general veg. cts   Viereck & Dyrness 1980 interior AK                 postfire cts       Foote 1983 MN: Boundary Waters      Conoe Area             general veg. cts   Ohman & Ream 1971 AB                          general veg. cts   Moss 1955 w-c AB                      forest cts         Corns 1983 w-c AB                      forest eas         Corns & Annas 1986 BC: Prince Rupert Forest      Region, Interior      Cedar-Hemlock Zone     general veg. eas   Haeussler & others 1984     Prince Rupert Forest      Region, Subboreal      Spruce Zone            general veg. eas   Pojar & others 1984 ON                          forest eas         Jones & others 1983

MANAGEMENT CONSIDERATIONS

SPECIES: Picea mariana
WOOD PRODUCTS VALUE : The principal commercial value of black spruce is pulpwood.  It is the most important pulpwood species in Canada, and is commercially important in the Lake States.  It is also used occasionally for lumber and a variety of other specialty items.  The wood is relatively light-weight but strong [65]. IMPORTANCE TO LIVESTOCK AND WILDLIFE : Browse:  Livestock and wild ungulates rarely eat black spruce.  Moose occasionally browse saplings, but white-tailed deer eat it only under starvation conditions [27].  Spruce grouse feed entirely on spruce needles during winter.  In Alaska, spruce grouse subsist on a diet of spruce needles from early November through March [21].  Black spruce is a major food of snowshoe hares, especially in winter.  One study found that consumption of black spruce by hares in interior Alaska varied seasonally as follows [69]:                 Dec-March   April    May    June-Sept   Oct-Nov                      (percent composition in diet) needles           38.5      27.6     12.4     12.3       26.0 bark and twigs    17.0      10.0      2.7      1.9        7.8 Seed:  Numerous seed-eating birds and small mammals feed on black spruce seed.  Red squirrels consume seed from harvested cones [42].  Mice, voles, shrews, and chipmunks consume seeds off the ground.  Chickadees, nuthatches, crossbills, grosbeaks, and the pine siskin extract seeds from open spruce cones and eat seeds off the ground [31,38]. PALATABILITY : The palatability of black spruce to big game and livestock is low to nil. NUTRITIONAL VALUE : Data from a nutritional study of black spruce needles collected in the winter on the Kenai Peninsula of Alaska are presented below [21]:             (percent chemical composition and caloric content)                             range           mean   protein                   4.4 - 6.5          5.7 fat                       5.5 - 7.1          6.2 crude fiber              21.7 - 23.5        22.47 ash                       1.9 - 2.8          2.33 Kilogram calories/100 g   502 - 517        508.9 In this study black spruce had a higher fat and caloric content than white spruce, but a lower ash content. Black spruce seeds are not as nutritious as white spruce seeds.  In Alaska, black spruce seeds averaged 6,053 cal/g, about 9 percent less than white spruce seeds [11].  COVER VALUE : Black spruce provides good cover for moose.  It often grows in dense stands and on moist substrates, conditions which provide cool bedding areas for moose [3].  Black spruce also provides good cover for spruce grouse [37].  In the Lake States, spruce grouse are dependent upon black spruce stands for much of their habitat needs.  The ruby-crowned kinglet, magnolia warbler, Cape May warbler, and ovenbird commonly nest in black spruce [38]. VALUE FOR REHABILITATION OF DISTURBED SITES : Black spruce is recommended for revegetating disturbed sites in boreal regions.  It may be useful for revegetating seismic lines, borrow pits, abandoned roads, and construction and well sites [10].  In southeastern Canada, Maine, and Minnesota, black spruce naturally invades well-drained raised surfaces in abandoned mined peatlands [23].  It can be established on disturbed sites by direct seeding or by transplanting nursery-grown seedlings. Special procedures have been developed for removing black spruce seed from the semi-serotinous cones [55].  Seeds retain their viability for several years when stored in sealed containers in a cool, dry environment [55].  Seeds require no stratification prior to sowing. They should be sown soon after snowmelt [10].  On peatland sites, seedling establishment is best when surface organic layers are exposed by burning or machine scarification.  On upland sites, exposing mineral soils before sowing is essential [38]. On well-drained soils 8- to 12-inch-tall (20-43 cm) bareroot transplants show good growth and survival when planted directly into organic layers [4].  Thus, site preparation which removes organic layers should not be undertaken when transplanting black spruce on uplands.  Transplant survival and growth are generally better following summer than spring outplanting [4].  In northeastern Alberta, overwinter survival of container-grown and transplanted black spruce seedlings was satisfactory on amended oil sand tailings [24]. Black spruce can be readily propagated by root cuttings [4]. OTHER USES AND VALUES : Black spruce is still harvested for Christmas trees, but recently the amount harvested from natural stands has declined [65].  In the past, specialty items made from black spruce included healing salves from the gum, antiscorbutic and diuretic beverages from twigs and needles, and rope from the roots [55]. OTHER MANAGEMENT CONSIDERATIONS : Timber harvest:  Clearcutting in strips or patches is generally considered to be the best silvicultural system for managing black spruce [38,65].  Most sites are broadcast burned and seeded naturally from nearby uncut stands [6].  Direct seeding has been used on large clearcuts in Minnesota.  On these cuts, seeding rates were 4 ounces (112 grams) per acre (approx. 100,000 seeds) to achieve 60 percent stocking, but 2 to 3 ounces (56-84 grams) were adequate on well-prepared sites [37].  On brushy sites, aerial spraying herbicides has been used to release black spruce [38]. Pests and diseases:  Eastern dwarf mistletoe (Arceuthobium pusillum) is the most serious disease of black spruce in the Lake States and eastern Canada.  It is less frequent in the West, and completely absent in northwestern Canada and Alaska.  Infection results in reduced vigor, witches brooms, deformed trees, and death.  Control is possible through silvicultural management [27,65].  Black spruce is susceptible to numerous needle rusts and fungi which result in defoliation and reduced vigor.  These diseases usually remain at low levels but may become epidemic [65].  Wind breakage is caused by butt and heart rots which are common in 70- to 100-year-old stands on upland sites and 100- to 130-year-old stands on organic sites [27,37].  The spruce budworm defoliates black spruce; however, black spruce is less susceptible than white spruce, red spruce, or balsam fir (Abies balsamea).  Black spruce trees most likely to be attacked are those growing with balsam fir and white spruce [27].  Numerous other insects attack black spruce but only occasionally cause serious damage [27,65]. Flooding:  Black spruce is susceptible to damage from flooding and disruptions in normal groundwater movements.  Trees have been killed over large areas where newly constructed roads impede water movements and where beavers dam drainage ditches or small streams [27].

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Picea mariana
GENERAL BOTANICAL CHARACTERISTICS : Black spruce is a native, coniferous, slow-growing, small upright tree or dwarf shrub.  Trees have a straight bole with little taper, and a narrow, pointed crown made up of short, compact, drooping branches with upturned ends [35].  Throughout much of its range, trees average 30 to 50 feet (9-15 m) in height and 6 to 10 inches (15-25 cm) in diameter at maturity [35].  In Alaska, black spruce is occasionally found as a medium-sized tree up to 60 feet (18 m) tall and 9 inches (23 cm) in diameter, but it is usually only 15 to 30 feet (4.5-9 m) tall and 3 to 6 inches (7.6-15.2 cm) in diameter [66].  Growth is quite variable depending upon site conditions.  In swamps in northeastern Minnesota, black spruce showed progressively slower growth rates from the border toward the center of swamps.  Eighty-year-old trees at a swamp border were, on average, 60 feet (18 m) tall, but only 120 feet (37 m) away at the center of the swamp trees were only 20 feet (6 m) tall [40]. Needles are 0.5-inch-long (1.2 cm), stiff, four-sided, dark bluish green [35].  The bark is thin, scaly, and grayish brown.  The root system is shallow and wide spreading.  Black spruce is very susceptible to windthrow except in the densest stands.  Most roots are found in the upper 8 inches (20 cm) of the organic soil horizons [65].  Cones occur in dense clusters in the upper part of the crown.  They are 0.6- to 1.25-inch-long (1.5-3.2 cm), nearly round or egg shaped, dull gray or blackish, and remain on the tree for several years [66]. In the extreme northern portion of its range, trees may be only 10 to 20 feet (3-6 m) tall and 1 to 2 inches (2.5-5 cm) in diameter when 100 to 200 years old [27].  In these extreme environments, needles and cones may be only one-half of their normal size [35].  Black spruce may form krummholz in the far north; here plant height equals the average snow coverage [20]. RAUNKIAER LIFE FORM : Phanerophyte REGENERATION PROCESSES : Cone and seed production:  Black spruce has the smallest seeds of North American spruces, averaging 404,000 per pound (890,000/kg) [55].  Trees can begin producing seed when as young as 10 years old but generally do not produce seed in quantity until they are 30 years old or older [65]. Some seed is produced every year, and bumper crops are produced about every 4 years [65].  Since seed crops seldom fail and the semi-serotinous cones release seeds over a period of several years, stands that are 40 years old or older nearly always have a continuous supply of seeds.  Annual seedfall in mature black spruce stands has been reported at [29,65]:      200,000 seeds/acre (494,000/ha) in Minnesota      990,000-1,692,000 seeds/acre (2.45-4.2 million/ha) in Ontario      404,000-1,900,000 seeds/acre (1.0-4.9 million/ha) in ne Ontario      240,000-528,000 seeds/acre (590,000-1,300,000/ha) near Inuvik, NWT      344,000 seeds/acre (850,000/ha) in central Alaska Dispersal:  Black spruce cones are semi-serotinous.  They remain partially closed and disperse seed over a period of several years.  In Minnesota, cones release about 50 percent of their seeds within 1 year after ripening, and about 85 percent within 5 years [68].  In northeastern Ontario, cones contained about one-half of their seeds after 5 years [29]; however, another study in Ontario found that after 3 years, cones retained only about 2 percent of their seeds [65].  Some of this variation is probably related to weather, as cones tend to open in warm, dry weather but remain closed in cold, wet weather [29]. Dispersal occurs throughout the year but is greatest in the winter and spring and lowest in the fall [65].  In northeastern Ontario, 58 percent of annual seedfall is dispersed in March, April, and May [29].  In Minnesota, annual seedfall was: 9 percent in August, 19 percent in September, 38 percent from October through April, 13 percent in May, 14 percent in June, and 7 percent in July [27].  Most seed is dispersed within about 264 feet (80 m) of a source [36]. Viability:  Germinative capacity of recently ripened seed is high, about 88 percent [55].  Viability decreases with age.  In northeastern Ontario viability of filled seed averaged 53 percent for 1- to 5-year-old seed, 20 percent for 6- to 10-year-old seed, and 5 percent for 11- to 15-year-old seed [29]. Germination and seedling establishment:  Black spruce seeds will germinate and establish on numerous substrates if the seedbed remains moist but not saturated, and free of competing vegetation [37]. Seedling establishment is best on mineral soils, sphagnum mosses, and rotten wood [16,65].  Seeds readily germinate on sphagnum mosses, probably because they are continually moist; however, seedlings are often overtopped and engulfed by the fast-growing sphagnums [27]. Feather mosses provide a poor seedbed because they have a tendency to dry out, but black spruce can establish in feather moss during wet years. Growth:  Seedlings are shade tolerant, but growth is fastest in full sunlight [37].  Seedlings rarely grow more than 1 inch (2.5 cm) in their first growing season.  Three-year-old seedlings are commonly 3 to 5 inches tall [27].  Roots of 1st-year seedlings may penetrate to 2 inches (5 cm) on upland soils, but when growing in mosses roots rarely reach depths of 1.5 inches (3.8 cm) after two growing seasons [27]. Vegetative reproduction:  Layering occurs when black spruce's lower branches become covered with mosses or litter. It is particularly common in swamps, bogs, and muskegs.  At the northern limit of trees across Alaska and northern Canada, black spruce reproduces almost entirely through layering [19].  Seeds may be produced, but few if any are viable.  SITE CHARACTERISTICS : Black spruce grows on both lowland and upland sites.  At the southern portion of its range it is found primarily on wet organic soils, but farther north its abundance on uplands increases.  In the Lake States and in New England, black spruce is most abundant in peat bogs and swamps, but is also common on transitional sites between peatlands and uplands.  In these areas it is rare on uplands, except in isolated areas of northern Minnesota and the Upper Peninsula of Michigan [36].  In Alaska, black spruce occupies poorly drained areas, such as cold wet flats, muskegs, and bogs, but is also common on north-facing slopes within 5 miles (8 km) of major rivers, and on upland slopes of all exposures more than 5 miles away from major rivers where white spruce is absent [25,66].  It often dominates sites in Alaska that are underlain by permafrost. Stand characteristics and associated trees:  Because fires occur at frequent intervals in black spruce forests, most stands are even-aged [see Plant Adaptations to Fire].  Black spruce commonly grows in pure stands on organic soils and in mixed stands on mineral soils [65].  On loamy or clayey moist uplands throughout the boreal region, associates include white spruce, quaking aspen (Populus tremuloides), balsam fir, paper birch (Betula papyrifera), and tamarack (Larix laricina) [27].  On organic sites in the Lake States and New England, black spruce mainly grows in pure stands, but it is also found in mixed conifer swamps with tamarack, northern white-cedar (Thuja occidentalis), balsam fir, and eastern white pine (Pinus strobus) [17,36].  Associated trees on mineral soil sites in this region include quaking aspen, paper birch, white spruce, and jack pine (Pinus banksiana) [36].  Jack pine is an especially common associate on dry, sandy and rocky sites [38].  Other common associates in the Lake States, especially in transitional areas between organic soil lowlands and mineral soil uplands, include black ash (Fraxinus nigra), red maple (Acer rubrum), American elm (Ulmus americana), balsam poplar (Populus balsamifera), eastern white pine, and red pine (Pinus resinosa) [36].  In northern New England and southeastern Canada, black spruce is sometimes associated with red spruce [38].  In western Canada, it may be found with lodgepole pine (Pinus contorta), subalpine fir (Abies lasiocarpa), and white spruce [27]. Understory:  A conspicuous characteristic of black spruce stands is a nearly continuous ground cover of feather mosses, sphagnum mosses, and/or reindeer lichens.  Reindeer lichens tend to dominate the ground cover in northern open black spruce woodlands.  Associated shrubs in bogs and swamps include Labrador-tea (Ledum groenlandicum), leatherleaf (Chamaedaphne calyculata), kalmia (Kalmia spp.), downy andromeda (Andromeda glaucophylia), bog blueberry (Vaccinium uliginosum), mountain cranberry (V. vitis-idaea), shrub birches (Betula glandulosa, B. pumila), and creeping snowberry (Gaultheria hispidula).  In the Lake States, speckled alder and red-osier dogwood (Cornus sericea) are the principal shrubs in some black spruce swamps.  Upland shrubs in the East include mountain maple (Acer spicatum), beaked hazel (Corylus cornuta), alders (Alnus spp.), and red raspberry (Rubus idaeus) [27,36,65]. Forest floor:  Stands in Alaska typically have a thick organic mat. Live moss-organic matter may be up to 20 inches (50 cm) thick [60]. Forest floor temperatures are typically lower and moisture content higher in black spruce forests than in white spruce, paper birch, quaking aspen, or balsam fir forests [59]. Soils and landforms:  Black spruce is tolerant of nutrient-poor soils. It is commonly found on poorly drained acidic peatlands [17,20].  On peatlands in Minnesota, black spruce grows best on dark brown to blackish, moderately decomposed peat that contains much partially decomposed wood [27].  Poor growth occurs on muskegs with thick accumulations of poorly decomposed yellowish-brown sphagnum peat.  In the northeastern United States, black spruce commonly grows on peat soils that are deeper than 12 inches (30 cm) [6].  On the Laurentian Shield in Minnesota, black spruce is frequently found on 10 feet (3 m) of peat, and sometimes on peat 60 feet (18 m) deep [27].  On mineral soil sites in northern Minnesota and adjacent Ontario, black spruce occurs on gravelly and bouldery loams and shallow soils over bedrock [27].  Throughout much of Canada, upland black spruce stands tend to occur on moist to somewhat wet clay loams and clays on long gentle slopes and lowlands [27].  In New Brunswick, Nova Scotia, and parts of Quebec, it occurs on sandy and gravelly outwash plains, river terraces, eskers, and related landforms [27].  In Alaska, black spruce stands underlain by permafrost tend to have shallow, mineral soil profiles [59].  Permafrost tables under black spruce stands in Alaska are often as shallow as 12 inches (30 cm) [18]. Elevation:  Black spruce is a tree of northern interior lowlands. Throughout its range it is generally found at elevations between 500 and 2,500 feet (152-762 m) [27]. SUCCESSIONAL STATUS : Black spruce is considered a climax species over most of its range. However, some ecologists question whether black spruce forests truly attain climax because fires in this forest type usually occur at 50- to 150-year intervals, while "stable" conditions may not be attained for several hundred years [61]. The frequent fire return interval in black spruce forests perpetuates numerous seral communities.  Throughout boreal North America, paper birch and quaking aspen are seral hardwoods that frequently invade burns in black spruce types [61].  Black spruce typically seeds in promptly after fire, and with the continued absence of fire, will eventually dominate the hardwoods.  Throughout much of Alaska, aspen and paper birch often dominate seral stands until they begin to break up at about 90 years, at which time black spruce attains dominance [25].  Since fires occur at 100-year or more frequent intervals, seral communities codominated by aspen and black spruce or paper birch and black spruce are common and widespread throughout Alaska. In southeastern Canada and the northeastern United States, balsam fir and northern white-cedar are more shade tolerant than black spruce and tend to replace it on "productive" sites [6].  Black spruce is a pioneer that invades the sedge mat in filled-lake bogs, but it may be preceded slightly by tamarack.  In time black spruce and tamarack may form a stable forest cover type in swamps.  However, as the peat soil is gradually elevated by the accumulation of organic matter, and the fertility of the site improves, balsam fir and northern white-cedar will eventually replace black spruce and tamarack [27,40]. Black spruce tends to replace jack pine and lodgepole pine on relatively dry sites in western Canada [27]. SEASONAL DEVELOPMENT : Black spruce flowers in late May or early June in the southern portion of its range and 1 to 2 weeks later in the northern portion.  Female conelets develop rapidly and contain mature seeds by about 3 months after pollination (late August or early September).  The cones release seeds gradually over a period of years [65]. Beginning and ending of height growth is generally as follows [27]:          Area       Height growth begins        Height growth ends      Lake States        June 8-20                  August 1-10         Maine      late May-early June          mid to late August        Alberta           June 1                     August 2

FIRE ECOLOGY

SPECIES: Picea mariana
FIRE ECOLOGY OR ADAPTATIONS : Plant adaptations to fire:  Black spruce produces seed at an early age, produces good seed crops regularly, and has persistent, semi-serotinous cones that release seed slowly over a period of years.  Thus, trees older than 30 years virtually always contain large amounts of seed. Following fire this large seed supply is released onto burned areas, allowing rapid seedling establishment.  Black spruce seeds are usually not destroyed by fire because the cones are located in the upper part of the crown where they are least likely to burn.  Thus, even when trees are killed by fire, cones usually retain viable seed.  Furthermore, the cones are small and occur in tightly compacted clusters, so that some seeds usually remain viable even after intense crown fires [71]. Immediately following fire large quantities of seeds are released.  In fact, striking recently fire-killed black spruce trees with an axe causes seeds to fall from scorched cones [40].  Within 60 days of a fire in an upland black spruce stand in Newfoundland which had an average tree height of 40 feet (12 m) and basal area of 188 square feet, 1,500,000 seeds per acre (3,705,000/ha) fell [68]. Delayed seedfall and delayed germination are additional postfire adaptations which ensure that some seed is always available to germinate and establish during postfire years with favorable growing conditions [57].  Although large amounts of seed do fall within the 1st postfire year, small amounts of seed will continue to be released for several years after fire.  Seedfall continued for 8 years following fire in a 70-year-old black spruce stand in interior Alaska [61].  Not all seed released immediately after fire germinates during the 1st postfire year. In New Brunswick, only 19 percent of black spruce seed artificially sown on burned areas germinated in the 1st postfire year, while 25 percent germinated in the 2nd postfire year [57]. Fire regime:  Wildfires are frequent and extensive in black spruce forests and usually prevent the development of uneven-aged stands [65]. Throughout much of the boreal region of Canada, spruce stands burn at 50- to 150-year intervals [34].  In interior Alaska, most black spruce stands burn before reaching 100 years in age [25].  Open black spruce woodlands (also called subarctic woodlands, open boreal forests, or lichen woodlands) in the Northwest Territories and in northern Quebec have fire intervals of 100 years or less [9,44,50].  Moving away from the relatively dry continental boreal forests toward the Atlantic seaboard, fire intervals become longer.  The longest fire-free intervals for spruce stands probably occur in southern Labrador, where the fire rotation for black spruce forests is estimated at 500 years [26].  Black spruce stands occurring in bogs and muskegs experience longer fire-free intervals than those in nearby upland stands do, and sometimes become uneven-aged [65]. POSTFIRE REGENERATION STRATEGY :    crown-stored residual colonizer; long-viability seed in on-site cones

FIRE EFFECTS

SPECIES: Picea mariana
IMMEDIATE FIRE EFFECT ON PLANT : Black spruce is easily killed by fire because it has thin bark and shallow roots.  Trees are often killed even by low-intensity surface fires.  Crowning is common in black spruce stands because low-growing, lichen-draped branches are easily ignited by ground fires.  Crown fires typically result in extensive mortality. In interior Alaska, most fires in black spruce stands are a combination of ground and crown fires that usually kill all black spruce [25]. Hanson [32] found that all black spruce trees were killed following a low-intensity surface burn (the top 2 to 4 inches [5-10 cm] of the 6 to 14 inch [15-35 cm] organic mat was consumed) in an open black spruce-tamarack community in interior Alaska.  This site contained 81 to 162 trees per acre (200-400/ha) that ranged from 40 to 178 years old and 1.5 to 3 inches (4-7 cm) in diameter. DISCUSSION AND QUALIFICATION OF FIRE EFFECT : NO-ENTRY PLANT RESPONSE TO FIRE : Closed boreal forests:  Following fire, fire-killed black spruce trees release large quantities of seeds over a period of 1 to 5 years, resulting in abundant seedling establishment.  Numerous authors report that in boreal forests black spruce seeds in promptly following fire. [25,42,50,63,68].  In interior Alaska, Foote [25] observed an average of 17,954 black spruce seedlings per acre (44,346/ha) on black spruce sites which had burned 1 to 5 years earlier.  By 50 years after fire, black spruce stands had naturally thinned to 2,595 stems per acre (6,402/ha); trees in these stands averaged 2.1 inches (5.4 cm) d.b.h. and were 16.4 to 23 feet (5-7 m) tall. Open woodlands:  In open black spruce woodlands in the Northwest Territories, black spruce seed production peaks when stand age reaches 100 to 200 years.  Fires occurring within this time frame have little effect on black spruce, as it quickly regenerates from seed.  Burning prepares good seedbeds by removing duff and competing vegetation, and by altering the thermal regime of the soil, which favors germination [9,10].  In open woodlands in northern Quebec, black spruce tends to regenerate quickly after fire, regaining or exceeding prefire density within 30years [56].  Moving northward from open woodlands to arctic treeline, the likelihood of successful black spruce seedling establishment following fire progressively diminishes. Forest-tundra ecotone:  In the forest-tundra ecotone north of open spruce woodlands in the Northwest Territories, black spruce seed production is poor, and generally little or no seed is available for postfire regeneration.  Where sparse seed production does occur, short-term climatic changes over a period of only 1 to 10 years could exhaust the seed population before a fire, or prevent seed germination after a fire.  Near arctic treeline in the Northwest Territories, black spruce stands do not regenerate following fire [9,10].  At treeline in northern Quebec, fires destroy or severely reduce black spruce and cause a shift toward arctic tundra.  Here, black spruce seedlings are only occasionally found after fire and are usually in depressions at the edge of burned areas where nearby living trees contain viable seeds [50]. DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : Following fire, black spruce establishes best where severe burning exposes mineral soils on upland sites or moist peat on lowland sites [40,72].  Unburned or partially burned sphagnum mosses are also good seedbeds, but unburned or partially burned feather mosses are poor seedbeds [2].  In southern Ontario, feather mosses are not wholly consumed by fire, but rotting logs under the feather mosses are often exposed and provide excellent seedbeds [45]. Experimental prescribed fires in a black spruce/feather moss stand in interior Alaska burned at varying fire severities, creating a mosaic pattern similar to that created by wildfire. Moisture content of the forest floor was critical in determining fire severity. Black spruce was expected to regenerate succesfully after these fires [64]. See the Research Project Summary of this study for further information. After an experimental burn on black spruce/feather moss sites in interior Alaska, naturally and artificially sown seeds germinated only where fire had removed part or all of the organic matter.  No seedlings were found on unburned surfaces or on scorched or charred feather mosses.  In general, exposed mineral soils provided the best seedbeds. Although seedlings established in areas where the organic layer was partially consumed, none survived past 3 years.  However, on sites where mineral soil was exposed, seedling frequency was 35 percent after 1 year, and 81 percent after 3 years, as a result of continued natural seedfall [72].  Following broadcast burning on black spruce/feather moss cut-overs (area thinned from 2,180 to 800 trees per acre [5,387-1,977/ha]) in southeastern Manitoba, black spruce seedling establishment and survival were better on moderate-severity than on light-severity burns.  Five years after burning, stocking was 94 percent in areas where burning depth averaged 4 to 7 inches (10-18 cm), 70 percent in areas where burning depth averaged 2 to 3 inches (5-8 cm), and 35 percent in unburned areas [15]. See the Research Project Summary of this study for further information. The Wickersham Dome Fire near Fairbanks, Alaska, burned 15,600 acres (6,300 ha) of mainly black spruce stands ranging in age from 50 to 125 years.  For 3 years after this fire, seedling establishment was quite variable in both lightly burned areas (<50 percent of ground surface blackened, litter depth reduced an average of 2.25 inches [5.7 cm], and 40 percent of ground vegetation alive 1 year after fire) and heavily burned areas (>90 percent of ground surface blackened, litter depth reduced an average of 4 inches [10.3 cm], and nearly all ground vegetation consumed).  In one heavily burned area, seedling establishment was slow, with only 20 percent of plots containing seedlings 3 years after the fire for a total of 1,113 seedlings per acre (2,750/ha).  Conversely, another heavily burned area contained 8,500 seedlings per acre (21,000/ha) 3 years after the fire.  In lightly burned areas, unburned and partially burned sphagnum mosses provided a good seedbed for black spruce so that by 3 years after the fire there were 16,200 seedlings per acre (40,000/ha) [62]. Black spruce seeds in quickly after fire on relatively dry uplands where it occurs with jack, red, or lodgepole pine.  However, the pines also seed in aggressively and quickly overtop black spruce.  A 35-year-old burn in northern Minnesota was composed mostly of jack pine and black spruce.  The jack pine were predominantly 33 to 34 years old and 4 to 6 inches (10-15 cm) in diameter, while the black spruce were 28 to 32 years old and 1 to 3 inches (2.5-3 cm) in diameter [33].  Black spruce is very shade tolerant and can survive in this suppressed condition for more than 100 years [33] and, in the absence of fire, will eventually replace the pines [8,65]. In southern Labrador, black spruce seedling establishment following fire is slow and progressive over a period of 70 to 100 years, resulting in uneven-aged stands.  Within spruce stands in this coastal climate, fires generally consume very little organic matter and leave only charred humus.  For the first 20 years after fire, seedling establishment is sporadic and largely restricted to depressions, the edges of water courses, and exposed mineral soils [26]. FIRE MANAGEMENT CONSIDERATIONS : Fire behavior:  In Alaska, Lutz [42] observed that burning in spruce stands tends to be more intense on ridges than in valleys, and that slopes with south or west exposures commonly have more mineral soil exposed after fire than slopes with north or east exposures.  On rocky slopes or ridges, fires are often unusually severe. The forest floor under most black spruce stands is made up of a thick organic mat [18].  Most fires do not consume the entire forest floor, but produce a mosaic of small patches of exposed mineral soil intermixed within larger areas of partially consumed organic material [25].  Late summer fires, however, sometimes consume the entire organic layer and expose extensive areas of mineral soil [61].  Burning black spruce stands in Alaska results in increased soil and forest floor temperatures and nutrient cycling rates.  This results in a warmer, more productive site for 10 to 20 years after fire [59]. Broadcast burning following timber harvest:  After clearcutting black spruce on organic sites in the Lake States, slash is often broadcast burned to aid natural regeneration.  Burning is generally recommended if there is heavy slash, a feather moss carpet, or abundant tall shrubs, grasses, or sedges [37].  For natural regeneration to be successful, an adequate seed supply is necessary, and fuels, including slash, litter, mosses, and peat, need to be sufficiently dry to allow for reasonably severe burns [15].  Aksamit and Irving [2] studied black spruce regeneration on numerous broadcast burned clearcuts in northern Minnesota.  They found that where the understory was dominated by sphagnum mosses before cutting, black spruce regenerated well regardless of the burning treatment.  In fact, adequate regeneration was obtained even without burning.  On feather-moss-dominated sites, prescribed burning was necessary to promote black spruce regeneration.  For burns to be effective on feather moss sites, they should be conducted when 100- and 1000-hour fuel moisture is less than 25 percent.  However, burning under these conditions may lead to fire control and mop up problems, and higher costs.  Where speckled alder dominates the understory before logging, natural regeneration of black spruce after broadcast burning is quite variable.  Low-intensity burns seem to favor black spruce regeneration, and more severe burns tend to favor other tall shrubs which compete fiercely with spruce seedlings.  Johnston [37] has outlined broadcast burning techniques for lowland black spruce in the Lake States. Eastern dwarf mistletoe control:  Prescribed burning can be used to eradicate eastern dwarf mistletoe in stands of black spruce.  For mistletoe control to be effective, burning must result in 100 percent black spruce mortality.  To ensure complete mortality, live trees can be cut to provide slash where understories are sparse, and/or diesel oil can be sprayed on slash when surface fuels are too thin or wet [74]. Frequent fires:  Black spruce normally seeds in aggressively following fire, but it can be eliminated from an area if a second fire occurs before these young trees reach seed-producing age [1].  Black spruce regenerated quickly following a 1923 fire in northern Ontario, but 8 years after a second fire in 1929 passed through the area, no black spruce seedlings were found [46].

REFERENCES

SPECIES: Picea mariana
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