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You are here >1Up Info > Wildlife, Animals, and Plants > Plant Species > Shrub > Species: Picea mariana | Black Spruce
 

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FIRE EFFECTS

SPECIES: Picea mariana | Black Spruce
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]. After an experimental burn on black spruce/feather moss sites in interior Alaska, naturally and artifically 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 [15]. 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. 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].

Related categories for Species: Picea mariana | Black Spruce

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Information Courtesy: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. Fire Effects Information System

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