Picea mariana

Picea mariana
Foliage and cones
Conservation status
Least Concern (IUCN 2.3)
Scientific classification
Kingdom:	Plantae
Division:	Pinophyta
Class:	Pinopsida
Order:	Pinales
Family:	Pinaceae
Genus:	Picea
Species:	P. mariana
Binomial name
Picea mariana (Mill.) Britton, Sterns & Poggenburg

Picea mariana (Black Spruce) is a species of spruce native to northern North America, from Newfoundland west to Alaska, and south to northern New York, Minnesota and central British Columbia. This area is also known as the taiga forest, in the Taiga and Boreal forests biome.

Description

Black Spruce at Lake Clark, Alaska.

Picea mariana is a slow-growing, small upright evergreen coniferous tree (rarely a shrub), 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 tall with a trunk 15-50 cm diameter at maturity, though occasional specimens can reach 30 m tall and 60 cm diameter. The bark is thin, scaly, and grayish brown. The leaves are needle-like, 6-15 mm long, stiff, four-sided, dark bluish green on the upper sides, paler glaucous green below. The cones are the smallest of all of the spruces, 1.5-4 cm long and 1–2 cm 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.

Natural hybridization occurs regularly with the closely related Picea rubens (Red Spruce), and very rarely with Picea glauca (White Spruce).

It differs from Picea glauca (White Spruce) 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 and pollen morphology also exist but require careful microscopic examination. From true firs, such as Abies balsamea (Balsam Fir), it differs in having pendulous cones, persistent woody leaf-bases, and four-angled needles, arranged all round the shoots.

Older taxonomic synonyms include Abies mariana, Picea brevifolia, Picea nigra.

Ecology

Growth varies with site quality. In swamp and muskeg it shows progressively slower growth rates from the edges toward the centre. The roots are shallow and wide spreading with fallen trees are colloquially called "drunken trees", and are often associated with thawing of permafrost. In the northern part of its range, ice pruned asymmetric Black Spruce are often seen, with diminished foliage on the windward side.

In the southern portion of range it is found primarily on wet organic soils, but farther north its abundance on uplands increases. In the Great Lakes States it is most abundant in peat bogs and swamps, also 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.

Black Spruce taiga, Copper River, Alaska.

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 a climax species over most of its range. However, some ecologists question whether Black Spruce forests truly attain climax because fires usually occur at 50-150 year intervals, while "stable" conditions may not be attained for several hundred years.

The frequent fire return interval, a natural fire ecology, perpetuates numerous successional communities. Throughout boreal North America, Paper Birch Betula papyrifera and Quaking Aspen Populus tremuloides 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, will eventually dominate the hardwoods.

It is a pioneer that invades the sedge mat in filled-lake bogs, though often preceded slightly by Tamarack Larch, Larix laricina, with which it may in time form a stable forest cover 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 Eastern Arborvitae Thuja occidentalis will eventually replace Black Spruce and Tamarack.

The larvae of the Spruce Budworm moth cause defoliation and if it occurs several years in a row will lead to death, though Black Spruce is less susceptible than White Spruce or Balsam Fir. Trees most at risk are those growing with Balsam Fir and White Spruce.

Uses and symbolism

Black Spruce is the Provincial tree of Newfoundland and Labrador.

The wood is of low value due to the small size of the trees, but is used for pulp and paper making.