Biology of the Black Spruce The black spruce (Picea mariana) is one of 8 species of coniferous or evergreen trees that are native to Manitoba. This group of plants belong to a larger group called the "Gymnosperms". These are plants that have true seeds (as opposed to the spores, used by so-called "lower plants"), but the seeds are exposed on the surface of the seed-bearing structure. The most familiar seed-bearing structure, though not the only kind in this group, is the "cone", from which the group draws one of its other common names, the "conifers" (cone-bearers). The word gymnosperm is derived from two Greek words: "gymnos", meaning naked or lightly clad, and "sperm", a seed. So, the gymnosperms are the "naked-seeded" plants. The bulk of plants that we regularly encounter, most flowers, trees and shrubs, are from the other group of plants that have true seeds, the Angiosperms. "Angio" is from the Greek "ang or angos" referring to a jar or container. The angiosperms are the "enclosed-seeded" plants. The other common name of this group of plants is "evergreens". The term evergreen derives from the habit of these plants not to shed their leaves (needles) at one particular time, as do deciduous plants. The needles of evergreens are just thick, waxy, needle-shaped leaves. Individual needles stay on the tree branch for more than one year, although each is eventually shed and replaced with new needles. Needles are shed continuously, though not all at once, as in deciduous trees that drop their leaves for the winter. One exception, however, is the tamarack (Larix laricina) which drops its soft needles each fall. It is a "deciduous evergreen". Tamaracks turn colour and drop their needles like a deciduous tree in autumn. Tamarack tree and needles in autumn. But what are the benefits of being evergreen? Needles, as opposed to the flattened, fleshy leaves of deciduous species, are well adapted for water conservation, thus giving evergreens an advantage over deciduous trees in conditions where soils are poor or non-existent (bare rocks and sand) and there is low water holding capacity. Deciduous trees need lots of water in the spring to "inflate" their newly emerging leafs. Evergreens can take advantage of water whenever it is available. And by having their leaves already formed in the spring they can start photosynthesizing earlier than deciduous plants, and can continue to produce food after other trees have lost their leaves, if favourable conditions persist later into the fall. In northern latitudes, high altitudes and areas with poor soil, evergreens often become the dominant tree species. Description The black spruce tends to be a medium sized tree growing to about 20 m in height and usually less than 50 cm trunk diameter. It has short needles (1-2 cm) that are densely packed around the branch tips. They are a dull blue-green colour, giving the overall tree a dark blue-green appearance. In Manitoba, black spruce may be confused with two other conifers, white spruce (Picea glauca) and balsam fir (Abies balsamea). Balsam fir may be distinguished from both spruces by its flattened arrangement of needles, its smooth, resin spotted bark and its upward pointing cones which break apart when mature. The spruces have needles surrounding the branchlets, scaly bark on their trunks and have downward hanging cones which persist long after the seeds have matured. Trunk of a black spruce. To tell a black spruce from a white spruce, examine the small branchlets, the cones and the habitat. Black spruce has tiny reddish hairs on the outermost branchlets and short needles (to 1.5 cm); white spruce has no hairs and has longer needles (to 2.5 cm). Black spruce cones are smaller (to a maximum of 3 cm) and rounder than white spruce cones (to 5 cm long). And finally, black spruce usually grows in low lying areas (bogs or edges of wetlands), whereas white spruce prefers upland sites. Black spruce will often grow in association with other moisture preferring species like tamarack, white cedar (Thuja occidentalis) and paper birch (Betula papyrifera), while white spruce is more often found with jack pine (Pinus banksiana), balsam fir and aspen (Populus tremuloides). Comparison of black and white spruce twigs and cones. (Black: to the bottom and left, white: to the top and right.) In urban areas, spruce trees are often used in landscaping, however, black spruce is rarely found as a planted species. Most urban spruce are either the native white spruce or the introduced species: Colorado blue spruce (Picea pungens), from western North America, or the Norway spruce (Picea abies), from Europe. When it grows in dense stands, in bogs or other low lying areas, a black spruce often loses most of its lower branches. These die as they become increasingly shaded by neighbouring trees. Often the top of the tree will appear densely branched, with the rest appearing rather spindly. Intense cone-clipping by red squirrels (the cone bearing branch tips are cut off and collected from the ground) is thought to play a role in pruning these uppermost branches of black spruce, promoting branching close to the main trunk and creating this dense growth. Red squirrel, here snacking on seeds from a jack pine cone. When it grows in more open conditions, black spruce is one of the classic "cone shaped" evergreen trees. (That's cone, as in the geometric shape, not the scaly seed-bearing structure.) Many spruce (Genus: Picea) and fir (Genus: Abies) trees, and some pines (Genus: Pinus) exhibit a very regular and symmetrical growth form that results in them appearing conical in shape. In silhouette they look like a narrow isosceles triangle with the apex pointing up. When most people think of a "pine" tree, this is the shape they think of, but most pines don't actually end up this shape. They tend to be less regular in their growth form, with upward pointing branch tips and often have twisted or branching trunks. It is actually the spruce and fir trees that most often exhibit the regular "pine" tree shape. (Sorry to be such a "nudge", but you know I'm a stickler for details like this.) The conical shape of many evergreens results from the simplicity of the way they grow. Most have one central, unbranching stem, or trunk, that grows straight up. Branches arise from the stem in whorls (actually, closely arranged alternate pairs), with several pointing outwards from the same point on the stem, at regular intervals. These grow out horizontally, perpendicular to the trunk, or at a slight upward angle. As the branches grow out from the stem, they tend to divide or branch only in the horizontal plane. (Only in the case where the top of the tree is damaged or broken off, will the tips of a branch start to grow up. One or more may eventually become the new trunk of the tree.) So, each set of branches encircling the trunk grows out like an ever expanding ring. The older the branches (the first to be sent out near the ground), the wider the ring, and as you proceed up the trunk the progressively younger branches have had less time to grow and spread. The overall effect is a symmetrical cone shaped tree. 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. Forest of black spruce. 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 jack pine. Black spruce, like any plant, is subject to a variety of damaging pests and diseases. These can include: Dwarf mistletoe (Arceuthobium pusillum), a parasitic plant that causes growth deformities and may lead to the death of trees. Various fungi, mainly "rusts" (Genus: Chrysomyxa) can infect and damage all stages of the tree from seedling to mature tree, even affecting seed production. Spruce budworm (Choristoneura fumiferana), the caterpillar of a small moth, eats the needles of this and other coniferous trees. Black spruce is not the favourite food of the budworm (they prefer balsam fir and white spruce), but in large infestations it can defoliate trees, resulting in slowed growth or even death. Snowshoe hares (Lepus americanus) can damage seedlings and sapling trees. Although they are not a preferred food item for the hares, in years when the hare populations are high, they will eat almost anything, including the tender buds and branches of young black spruce. 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. "Black spruce comprises 31% of the available wood in Manitoba's annual allowable cut, making it the most abundant species in the province, by volume. Because of its long wood fibers, black spruce is the preferred species of Repap Manitoba for kraft paper and Pine Falls for newsprint." "Black spruce cover type dominates 5.8 million ha of Manitoba's Forest Zone. Intermediate-age trees comprise 127.9 million cubic metres in all cover types, mature 70.5 million cubic metres and over mature 10.1 million cubic metres." "Open zone Annual Allowance Cut (AAC) volume on provincial Crown Lands is 2.8 million cubic metres." (That's about 1.3% of the available black spruce wood per year, whereas fire consumes about 2.4% annually.) 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. 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