Black Spruce
|
|
| Black Spruce Conservation status: Secure | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Missing image Picea_mariana.jpg Image:Picea mariana.jpg Black Spruce at Lake Clark, Alaska | ||||||||||||||
| Scientific classification | ||||||||||||||
|
The Black Spruce (Picea mariana) is a common coniferous tree in North America, ranging from Newfoundland west to Alaska, and south to northern New York, Minnesota and central British Columbia. Old synonyms include Abies mariana, Picea brevifolia, Picea nigra.
It is a slow-growing, small upright tree or shrub, having a straight trunk with little taper, and a narrow, pointed crown of short, compact, drooping branches with upturned tips. Through much of its range it averages 10-15 m (30'-50') tall with 15-25 cm (6"-10") diameter trunks at maturity, though occasional specimens can reach 24 m tall and 50 cm diameter. Growth varies with site conditions. In swamps it shows progressively slower growth rates from the edges toward the centre. The roots are shallow and wide spreading with most in the upper 20 cm (8") of organic soil. It is very susceptible to windthrow except in the densest stands.
The bark is thin, scaly, and grayish brown. The leaves are needle-like, 8-12mm (½") long, stiff, four-sided, dark bluish green. The cones are the smallest of any spruce, 2-4 cm long (0.6"-1.25"), spindle-shaped to nearly round, dark purple ripening red-brown, in dense clusters in the upper crown, opening at maturity but persisting for several years.
Natural hybridization between species of spruce is usually rare, but does occur regularly with the closely related Red Spruce Picea rubens.
It differs from White Spruce Picea glauca, in having shorter needles, smaller and rounder cones, and a preference for wetter lowland areas. From true firs, such as Balsam Fir Abies balsamea, it differs in having pendulous cones, persistent woody leaf-bases, and four-angled needles, scattered and pointing in every direction.
It grows in both lowland and upland sites. In the southern portion of range it is found primarily on wet organic soils, but farther north its abundance on uplands increases. In the Lake 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.
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 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.
Black Spruce is the Provincial tree of Newfoundland.
External links
- Gymnosperm Database: Picea mariana (http://www.botanik.uni-bonn.de/conifers/pi/pic/mariana.htm)
- Flora of North America: Picea mariana (http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=233500911)