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Biology of Black Spruce - Part 2

 

 

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Black Spruce

Biology of the Black Spruce - Part 2

By Johnny Caryopsis (Click links for more images.)

Classification

Here is the formal taxonomic classification of the black spruce.

Kingdom: Plantae
Division: Spermatophyta
Subdivision: Gymnospermae
Class: Coniferinae
Family: Pinaceae
Genus: Picea
Species: mariana

Name Derivation

The scientific name for black spruce works out like this:

"Picea" derives from the Latin word "pix" which means pitch. Pitch is a dark coloured resinous substance that was once used to caulk seams in wooden ships. In this case, the pitch refers to the resins that exuded from spruce and pine trees, although real pitch was derived from coal tars.

"mariana" derives from the New Latin word "marianus", meaning "from Mary, the mother of Jesus". (Interesting that this species was until recently the dominant Christmas trees in Manitoba!) The black spruce was first described in the early 1700's as the "Maryland Spruce", hence the "mariana" appellation, though it does not occur there. Remember, common and scientific nomenclature can often be quite a muddle!

The current common names of this species include black spruce, swamp spruce and bog spruce. The latter two names make sense as they relate to the habitat of the species, but I wasn't able to track down how the common name of "black" spruce derives.

Habitat and Range

Black spruce is essentially a "Canadian" species; that is, the bulk of it's North American range is in Canada. It is found in a few northeastern states in the US, as well as in Alaska. In Manitoba, this species occurs throughout the province except in the extreme north east, beyond the tree-line, and in the extreme south west, in the dry prairie region.

Typical habitat of black spruce and white spruce.

In the southern parts of its range the black spruce is usually found in habitats that have wet organic soils, such as peat bogs. Though they grow in places with very moist soil, they do not tolerate having their roots under water for long. It is common to see stands of dead black spruce where beavers have flooded adjacent bog lands. Black spruce can tolerate a variety of poor soil conditions, even growing on scarcely covered bare rocks. Further north it becomes more and more dominant on these kinds of conditions. In Manitoba it is one of only 2 or 3 tree species left at the tree-line that separates the last of the boreal forest from the arctic tundra. In the far north much of the black spruce's habitat is underlain by permafrost. It's thought that the tree's shallow rooting habit plays a role in it's dominance at these high latitudes. The roots of black spruce tend to spread out from the main trunk in a ring just at or below the soil surface, or right on top of the rocks in some case. They form a flattened circle about the tree, so the trunk is supported like a post sitting on a plate.

Black spruce stand in lowland.

Life Cycle

Every black spruce tree has grown from a tiny, winged seed (it would take 900 seeds to make 1 gm) that was released from its parent's cone, fluttered to earth and happened to find the right conditions to germinate and grow. Under good growing conditions it may have reached 2-4 m in height by age 10, and 12 m by age 40 (tree growth rates are highly variable and dependent on many conditions). Black spruce can grow to reach heights up to 20 m and are thought to live as long as 280 years, though few are thought to reach this age, owing to the prevalence of forest fires and logging in the boreal forest.

The dominant feature in the life cycle of the black spruce, and all other coniferous trees, is the cone. A cone, which may also be called a "strobilus", consists of a central axis which is surrounded by tightly packed, thick scales. There are male cones which produce pollen and female cones with egg cells where the seeds will ultimately develop. Both kinds of cones are found together on individual trees of most conifers, including the black spruce; that is, they are monecious. Female cones of black spruce are produced mainly in the upper crown of the tree (the top 1 or 2 m), with the male cones developing in the branches just below these.

Cones develop to the bud stage in the year prior to their use in reproduction. In the following spring, the small male cones (about 1.5 x 0.5 cm) swell and open in late May through early June, releasing yellow pollen grains on the wind. The female cones (about 2 x 1 cm) open at the same time and are pollinated by the wind borne pollen. The arrangement of male and female cones on individual trees, with female cones higher up, helps to promote cross-pollination from trees some distance away. After releasing pollen, the male cones shrivel and drop off. The female cones remain on the tree and the seeds mature about 3 months after being fertilized. The female cones grow to be 2.5 x 1.5 cm by the time the seeds are ripe. The winged seeds are released starting in late August and are dispersed for short distances by the wind.

The cones of black spruce don't open fully and can remain on the tree for several years, so seeds from a single cone may not fall for more than a year after they were formed. The seeds can remain viable for many years. Overall seed production will vary greatly from year to year in any given region, but will tend to be very high once every 3-6 years. These infrequent bursts of seed production are common among most trees. It is an adaptation to ensure that, every once in a while, seed production far exceeds what the array of seed predators (squirrels, mice, birds, etc.) can eat. By "flooding the market" the trees ensure that some seeds will get a chance to grow and ultimately replace the parent trees.

Vegetative Reproduction

Black spruce occasionally reproduce asexually by a process called "layering". Lower branches that are pressed down onto the ground may eventually form roots and the outermost branch tips will begin to grow upward to start a new trunk. In this way a single tree may eventually become a small grove of trunks. This process occurs mainly in sparse stands of spruce growing in poor soils, and is most common towards the northern end of the species range, at the tree line.

Ecological Significance

Manitoba doesn't have that many species of trees to begin with (only 24, or thereabouts), so all our trees are vital for the role they play in creating forests. Over much of the central and northern part of our province, the black spruce is one of the most dominant tree species, so it is a major player in the creation of forest habitat for many other plant and animal species. It is the dominant tree species in lowlands throughout the boreal forest, providing food and shelter for animals such as the red squirrel (that eats the seeds from the cones), fisher and marten (that eat red squirrels), and birds like the boreal owl (which hunts for voles and shrews among the dense spruce groves) and the spruce grouse (which feeds on the buds of various conifers in winter). Because the seeds of black spruce often remain in the cones, they are an important food source for birds such as pine siskin, crossbills and pine grosbeak. Black spruce also forms important habitat for one of Manitoba's rarest species, the woodland caribou.

Dangers and Diseases

Fire is a major factor in all forest types in Manitoba. The periodic droughts that afflict all parts of our province leave our forests open to wildfires. In the boreal forests, fire (most often from lightning strikes) is a regular player on the ecological stage and the plant and animal species that occur there are adapted to the drastic changes that fire brings. For tree species this means shorter overall life spans and emphasis on adaptations to quickly repopulate burned areas. Black spruce are easily damaged or killed by fire, but are well adapted to prosper in post-fire conditions. Fire helps to open remaining cones. Young seedlings do well in the open seed-bed prepared by the fire's removal of the existing vegetation.

During the early 1990's fire consumed more black spruce annually than did commercial logging, about 5 million cubic metres burned compared to about 3 million cubic metres harvested. But it should be remembered that forestry consumes trees at a fairly consistent rate, while fire losses vary wildly from year to year. (Source: Forestry Branch, Manitoba DNR, 5-Year Report to the Legislature 1997.)

Snow can have a major impact on the health and survival of a black spruce tree. A major drawback of being "evergreen", is that snow will accumulate on the needle covered branches. Over the course of a winter, a tree may end up carrying hundreds of kilograms of snow on its branches. That's enough weight to break branches. Strong winds can snap off the snow laden tops of trees. The weight of the snow can start a tree leaning, and a black spruce whose trunk has gone off vertical is doomed. In future winters the snow will pile up unevenly and put more and more force on the tree, eventually knocking it over.

Snow accumulation on a White Spruce.

Black spruce, like any plant, is subject to a variety of damaging pests and diseases. These can include:

Human Uses

Black spruce trees are harvested mainly for the pulp and paper industry (it is the most important pulp wood species in Canada), but occasionally for lumber (the yellowish coloured wood is both light weight and strong) and fuel wood (fire wood), and for use as Christmas trees. Keith Knowles with Forestry Branch, Manitoba Natural Resources, estimated that black spruce makes up about 20% of the current Christmas tree market in this province. As a kid, I don't remember seeing much other than black spruce trees on lots in Winnipeg, but in latter decades Christmas tree farming has made different tree species available at prices to rival the wild harvested spruces, and black spruce seem to be harder to find in tree lots these days.

Here's some more information I got from Keith, from Forestry's most recent 5-Year Report to the Legislature (1997), on the economic significance of the black spruce.

A Last Word

Black spruce will always hold a special place in my heart, since it was central to so many of my Christmases past. But it is also one of Manitoba's most important trees for tomorrow. It is a dominant species and the basis for wildlife habitat over much of our boreal forest region. Harvesting this tree provides jobs and helps support rural economies throughout our province. The ecological and economical importance of black spruce makes this a vital species for us all.

Thanks for learning about this Black Spruce trees! Bye for now!

Here's some more winter articles you might enjoy:

Ruffed Grouse | Winterkill! | Makin' Tracks!

Acknowledgments

The information in this article was drawn from a variety of sources, including the following:

Biology of Plants, 2nd Edition. 1976. By P.H. Raven, R.F. Evert and H. Curtis. Worth Publishers Inc., New York. ISBN 0-87901-054-1

Budd's Flora of the Canadian Prairie Provinces. Revised by J. Looman and K. F. Best. 1987. Research Branch, Agriculture Canada Publication 1662.

Keith Knowles, with Forestry Branch, Manitoba Natural Resources provided some information from the Manitoba Forestry - 5 Year Report to the Legislature (1997).

Dan Bulloch, with Forestry Branch, Manitoba Natural Resources, provided some information and reviewed this article for accuracy.

St. Paul Field Office - Forest Resources Management and Forest Health Protection, USDA Forest Service, State and Private Forestry - Web site: http://willow.ncfes.umn.edu/ (An excellent source for forest information on the Web.)

Here are some other publications with useful information about the black spruce and other trees in Canada.

Identification Guide to the Trees of Canada. 1989. By J. Lauriault. National Museum of Natural Sciences. Pub. by Fitzhenry and Whiteside, Markham, Ont. ISBN 0-88902-654-9

Native Trees of Canada. 1990. By R.C. Hosie. Published by Fitzhenry and Whiteside Ltd. and Supply and Services Canada. ISBN 0-88902-572-4

Plants of the Western Boreal Forest and Aspen Parkland. 1995. By D. Johnson, L. Kershaw, A. MacKinnon and J. Pojar. Lone Pine Publishing, Edmonton, Alta. ISBN 1-55105058-7
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