| Black spruce | |
|---|---|
 | |
| Stand of black spruce nearInuvik,Northwest Territories, Canada | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Gymnospermae |
| Division: | Pinophyta |
| Class: | Pinopsida |
| Order: | Pinales |
| Family: | Pinaceae |
| Genus: | Picea |
| Species: | P. mariana |
| Binomial name | |
| Picea mariana (Mill.) Britton, Sterns & Poggenburg | |
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| Synonyms[2] | |
Synonymy
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Picea mariana, theblack spruce, is a North Americanspecies ofspruce tree in thepine family. It is widespread across Canada, found in all 10 provinces and all 3territories. It is the official tree ofNewfoundland and Labrador and is that province's most abundant tree. Its range extends into northern parts of the United States: inAlaska, theGreat Lakes region, and the upperNortheast. It is a frequent part of thebiome known astaiga or boreal forest.[3][4][5][6][7]
The Latinspecific epithetmariana means "of the Virgin Mary".[8]
P. mariana is a slow-growing, small uprightevergreenconiferoustree (rarely ashrub), having a straight trunk with little taper, a scruffy habit, and a narrow, pointed crown of short, compact, drooping branches with upturned tips. Through much of its range it averages 5–15 m (15–50 ft) tall with a trunk 15–50 cm (6–20 in) diameter at maturity, though occasional specimens can reach 30 m (98 ft) tall and 60 cm (24 in) diameter. Thebark is thin, scaly, and greyish brown. Theleaves are needle-like, 6–15 mm (1⁄4–9⁄16 in) long, stiff, four-sided, dark bluish green on the upper sides, palerglaucous green below. Thecones are the smallest of all of the spruces,1.5–4 cm (1⁄2–1+1⁄2 in) long and1–2 cm (1⁄2–3⁄4 in) broad, spindle-shaped to nearly round, dark purple ripening red-brown, produced in dense clusters in the upper crown, opening at maturity but persisting for several years.[3][4]
Naturalhybridization occurs regularly with the closely relatedP. rubens (red spruce) and very rarely withP. glauca (white spruce).[3] It differs fromP. glauca in having a dense cover of small hairs on the bark of young branch tips, an often darker reddish-brown bark, shorter needles, smaller and rounder cones, and a preference for wetter lowland areas. Numerous differences in details of its needle andpollen morphology also exist but require careful microscopic examination to detect. From truefirs, such asAbies balsamea (balsam fir), it differs in having pendulous cones, persistent woody leaf-bases, and four-angled needles, arranged all round the shoots.
Due to the large difference betweenheartwood andsapwood moisture content, it is easy to distinguish these two wood characteristics inultrasound images,[9] which are widely used as anondestructive technique to assess the internal condition of the tree and avoid useless log breakdown. Oldertaxonomic synonyms includeA. mariana,P. brevifolia, orP. nigra.
Growth varies with site quality. In swamp andmuskeg it shows progressively slower growth rates from the edges toward the centre. The roots are shallow and wide spreading, resulting in susceptibility towindthrow. In the northern part of its range,ice pruned asymmetric black spruce are often seen with diminished foliage on the windward side.[10] Tilted trees colloquially called "drunken trees" are associated with thawing ofpermafrost.[3][11]
In the southern portion of its range it is found primarily on wet organic soils, but farther north its abundance on uplands increases. In theGreat Lakes region it is most abundant in peatbogs and swamps, also on transitional sites between peatlands and uplands. In these areas it is rare on uplands, except in isolated areas of northernMinnesota and theUpper Peninsula of Michigan.
Most stands are even-aged due to frequent fire intervals in black spruce forests. It commonly grows in pure stands on organic soils and in mixed stands on mineral soils. It is tolerant of nutrient-poor soils and is commonly found on poorly drained acidic peatlands. It is considered aclimax species over most of its range; however, some ecologists question whether black spruce forests truly attain climax because fires usually occur at 50 to 150 year intervals, while "stable" conditions may not be attained for several hundred years.[3] The frequent fire return interval, a naturalfire ecology, perpetuates numerous successional communities. Throughoutboreal North America,Betula papyrifera (paper birch) andPopulus tremuloides (quaking aspen) are successional hardwoods that frequently invade burns in black spruce. Black spruce typically seeds in promptly after fire and with the continued absence of fire eventually dominates the hardwoods.
Black spruce is apioneer that invades thesphagnum mat in filled-lake bogs, though often preceded slightly byLarix laricina (tamarack). Black spruce frequently out-competes shade-intolerant tamarack in the course of bog succession.[12] 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 (Thuja occidentalis) eventually replace black spruce and tamarack. On drier sites following fires, black spruce can take over stands of faster growingjack pine (Pinus banksiana) by virtue of its ability to grow in partially shaded conditions which inhibit pine seedlings.[13] But black spruce seedlings are intolerant to the low light and low moisture conditions under mature spruce stands. Balsam fir and northern white cedar, both more understory-tolerant species with deepertaproots, survive and eventually succeed the spruce in the absence of fire.[14]
Thespruce budworm, amoth larva, causes defoliation which kills trees if it occurs several years in a row, though black spruce is less susceptible than white spruce or balsam fir. Trees most at risk are those growing along with balsam fir and white spruce.[15]
Numerouscultivars have been selected for use in parks and gardens. The cultivarP. mariana 'Nana' is a dwarf form which has gained theRoyal Horticultural Society'sAward of Garden Merit.[16][17] Picea mariana is known to hybridize with Serbian spruce,Picea omorika. The hybrid isPicea machala, and hybrids withSitka spruce are known as well.[citation needed]
Black spruce is theprovincial tree ofNewfoundland and Labrador. The timber is of low value due to the small size of the trees, but it is an important source ofpulpwood and the primary source of it in Canada.[18] Fast-foodchopsticks are often made from black spruce.[5] It is increasingly being used for makingcross laminated timber by companies such as Nordic Structures, which allows the high strength due to the tight growth rings to be assembled into larger timbers.[19] Along with red spruce, it has also been used to makespruce gum andspruce beer.[20]
Media related toPicea mariana at Wikimedia Commons
