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Linzhi Spruce
Picea linzhiensis
Black Spruce
Picea mariana
  (Mill.) Britton, Sterns & Poggenb.
Martínez's Spruce
Picea martinezii
  Owner:   C. Michael Hogan    

Black Spruce summer foliage in Håbo, Uppland. @ Håkan Andersson
Black Spruce
Picea mariana

C. Michael Hogan PhD
November 24, 2008

This slow growing narrowly conical upright conifer is native to Canada and the extreme northern USA. In the far northern part of its range, Black Spruce is noted for its dwarfing and its distinctive asymmetrical form sculpted by "ice pruning". Controlled by frequent wildfires, P. Mariana stands uncommonly achieve an uneven size distribution. Preferring soils that are peaty or rich in organic material, P. mariana is able to out-compete other tree species in many parts of its range, and is also dominant where rooting depth is limited over permafrost.



DISTRIBUTION AND FOREST TYPES

Black Spruce forest on the Hudson Bay Plain, Manitoba. @ C. Michael Hogan
The species is transcontinentally distributed from Alaska to Newfoundland and ranges north to Hudson Bay and south to Minnesota. In Alaska its range extends north to the south slopes of the Brooks Range, and as far west as the the upper Kobuk River and Elim on the Seward Peninsula; it is also found at the margin of the Cook Inlet and on the Kenai Peninsula as far as Naknek .along Bristol Bay. Also in Alaska it occurs in the Yukon River and Kuskokwim River Valleys as well as the Copper River Valley as far south as Tonsina. It is commonly found on muskegs and other boggy areas, often in the southern range as a pioneer. Chief forest types include Black Spruce/Feathermoss, Black Spruce/Sedge, Black Spruce/Speckled Alder and Black Spruce/Spaghnum Bog Forest.

The Black Spruce/Feathermoss climax forest occurs in the south to central range and exhibit moderately dense canopy featuring a forest floor of feathermosses (e.g. Hylocomium splendens, Pleurozium schreberi, Ptilium crista-castrensis). Black Spruce/Sedge forest manifests open stands of dwarfed trees on wet sites with the understory dominated by sedges, grasses and mosses (but not sphagnum) Black Spruce/Speckled Alder forests occur where groundwater is perched, at least during the summer. Black Spruce/Sphagnum Bog forests are found above humus rich or moist high mineral soils with extensive dwarf shrub and sphagnum mosses understory. Typically in the northerly part of its range Black Spruce forests are dwarfed and sparse, exhibiting severe "ice pruning". In these northern forests there are many lichen species that thrive on exposed boulders on the forest floor (e.g. Worm lichen, Finger lichen, Jewel lichen, Map lichen, Pixie cup, Sunburst lichen and Rock tripe)

Pollen core analysis indicates that P. mariana and P. glauca both invaded central Alberta as recently as the early Holcene, (Begon) with peak densities occurring about 3400 BC outstripping the populations of P. glauca, which thrives on high mineral mesic soils; it is likely that these peak densities of P. mariana correspond to a point in time where organic material had time to accumulate, this rich humus being the preferred soil for Black Spruce.
Black Spruce cone from Håbo, Uppland. @ Håkan Andersson



MORPHOLOGY
{This is an upright tree with a narrow crown attaining ten to 15 meters in height except for the northernmost part of its range, where growth is dwarfed from the shield geology, shallow permafrost and abbreviated growing season. Trunks of the Black Spruce are only about 15 to 40 cm in diameter, and lesser in the far north. The thin bark is somewhat scaly and brown, and twigs are hairy. Branches are very short, and dead branches are retained for many years. The short stiff evergreen needles are four-sided. The common name "Black Spruce" derives from the dark green foliage, and likely from the very dark contrast in snowy environments, where ice-pruning also accentuates the woodiness. (Ice pruning is the phenomenon, whereby windward branches are selectively pruned by wind driven snow and ice, preferentially defoliating the windward side leaves.)

The shallow root architecture is ideally adapted to thin soils atop shallow permafrost and rocky shield formations; for these reasons Black Spruce is a dominant tree in its northern range. Nevertheless, shallow rooting renders this species vulnerable to wind-throw. The monoecious flowers feature purple female flowers and red male structures, the latter turning yellow in the late summer. The cones are more diminutive than any other spruce, measuring 1.5 to three cm in length.(Viereck) These grayish black fruits are ovoid to spherical and are concentrated in the upper portion of the crown.



ECOLOGY
Ice pruned Black Spruce, Churchill. @ C. Michael Hogan
P. mariana stands characteristically are the lowest in biological productivity of Boreal forests, (Barbour) likely due to the species tolerance for soils poor in nutrients; however, Black Spruce, like most Boreal conifers, is very efficient in utilization of available nitrogen compared to deciduous species, especially in nutrient limited environments..(Reichle)

When bogs reach a eutrophic climax and create a sedge mat, Larix laricina and P. mariana typically are first invaders; after more thorough Black Spruce establishment, the soil fertility may advance, with Abies balsamea and Thuja occidentalis generally replacing the pioneers On the Great Slave and Keller Lake plains, an early colonization stage is sometimes a raised polygonal permafrost bog with isolated Black Spruce in windswept krumholz forms.

Fire incidence promotes frequently recurring successional communities. Hardwoods Betula papyrifera and Populus tremuloides are pioneer invaders to burns of Black Spruce. Since P.mariana seeds rapidly subsequent to a forest burn, it will typically advance to a dominant position over the successional hardwoods.

In the far northern range of Black Spruce an interesting but abbreviated palette of mammals subsist; for example, in the late fall I have observed Ursus maritimus migrating to the forming ice pack (Hogan) and arctic fox. A limited number of birds occur in association with the far northern Black Spruce forests. In the western Hudson Bay Plain, I observed the Gray Jay, Gyrfalcon, Willow Ptarmigan and Corvus corax; easterly in Labrador others report the Rock Ptarmigan, Snow Bunting and Wheatear. (Boston) Spruce budworm larvae can defoliate P. mariana, leading to tree death if these events recur in several successive years
Dwarfed Black Spruce savanna on the Hudson Bay Plain



CONSERVATION
Special consideration may be warranted for recent burned Black Spruce forests, since these regimes are associated with high bird biodiversity.(Burton) Furthermore, old growth Black Spruce forests merit protection, since they offer unusually high densities of Rangifer tarandus, which species is threatened in some local areas. Efforts need to be taken to prevent habitat fragmentation since some of the large mammalian species (e.g. Ursus Maritimus and Rangifer tarandus) depend on considerable migration distances; moreover, continuity of habitat in the harsh north is highly desirable to promote Rescue Effect for many species of plants and animals. These needs are amplified due to threats of climate change, and resulting enhanced demands on faunal migration.



REFERENCES
Michael Begon and Alastair H. Fitter (1993) Advances in Ecological Research: Volume 24,
Academic Press, 410 pages ISBN 0120139243
* Leslie A. Viereck, Elbert L. Little, Jr., Elbert uther Little, George W. Argus (2007)
Alaska Trees and Shrubs, University of Alaska Press, 370 pages ISBN 1889963860
* Michael G. Barbour and William Dwight Billings (2000) North American Terrestrial Vegetation, Second edition, Cambridge University Press, 708 pages ISBN 0521559863
* David E. Reichle (1981) Dynamic Properties of Forest Ecosystems, Published by CUP Archive, 683 pages ISBN 0521225086
* C.Michael Hogan (2008) Polar Bear: Ursus maritimus, GlobalTwitcher, ed. Nicklas Stromberg
* Boston Society of Natural History (1907) Proceedings of the Boston Society of Natural History
* Philip Joseph Burton and W. L. Adamowicz (2003) Towards Sustainable Management of the Boreal Forest, NRC Research Press, 1039 pages ISBN 0660187620



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