Vegetation Regions

Vegetation regions are geographical areas characterized by distinct plant communities. Community composition, determined primarily by climate (eg, temperature, precipitation, sunlight), may be affected by factors such as geology, soil composition and erosion, water drainage patterns and human interference. Each vegetation region supports a characteristic animal community which may affect its composition. The principal regions represented in Canada are as follows.

Arctic Tundra

The arctic tundra is the second-largest vegetation region in the country. It covers a greater range of latitude than any other yet is little understood because of its remoteness and sparse human population. The Arctic is treeless because of its low summer temperatures (a mean of less than 11° C in the warmest month) and short growing season (1.5-3.5 months). The transition from boreal forest to tundra, termed forest-tundra, consists of ribbons or islands of stunted black and white spruce trees in a sea of tundra vegetation. Only a few birch and trembling aspen reach this far north.

The major environmental factors which limit plant growth and distribution are cold soils with an active layer in summer of 20-60 cm above the permafrost; varying depth of winter snow; low levels of soil nutrients, especially nitrogen and phosphorus; and soils that can be very dry (on ridges) or very wet (in lowlands) in summer. The Arctic is often divided into the Low Arctic of the mainland and the High Arctic of the northern District of Keewatin and Arctic Archipelago.

Boreal Forest or Taiga

The Boreal Forest or Taiga encircles the Northern Hemisphere between the treeless Arctic Tundra and the more southerly midlatitude broad-leaved forest zones. In North America, the Taiga extends from the interior of Alaska and the eastern slopes of the Rocky Mountains to Newfoundland, making it the largest vegetation region in Canada. A separate area of boreal vegetation also occurs on Cape Breton Island, along the east coast of Nova Scotia and around the Bay of Fundy.

This vegetation region is dominated by plants that are capable of surviving cool, short summers and long, cold winters. Variations in vegetation occur within this large biome.

Pacific Coastal

The Pacific Coastal region, which ranges from nearly 48° N latitude to 55° N, may be divided into 4 distinct growing zones reflecting the great variation in temperature, length of growing season and average precipitation (650-3000 mm per year). Significant rainfall shadows, caused by mountain ranges on Vancouver Island and Haida Gwaii, can produce further climatic variation on the eastern flanks of the mountain ranges and in associated mainland coastal areas.

Vegetation of the outer coasts of island archipelagoes and the exposed coasts of the mainland is predominantly coniferous forest consisting of Douglas fir, western hemlock, yellow cypress, Sitka spruce, shore pine, western red cedar and occasionally western yew. The principal deciduous hardwoods are red alder and Scouler willow. Douglas fir is absent from Haida Gwaii.

The Georgia Strait area on the east coast of Vancouver Island and the adjacent mainland have a drier, Mediterranean climate. Here, coastal vegetation must persist through a hot, dry period lasting up to 8 weeks. The vegetation is characterized by a colourful spring flora with several annual herbaceous species. Arbutus, western flowering dogwood and Garry oak reach their northern limits in this region. Arbutus is the only native broad-leaved evergreen tree in Canada. Pacific dogwood is the provincial floral emblem of BC. Other forest species include Douglas fir, western hemlock, grand fir, bigleaf maple, western red cedar and bitter cherry.

The predominant undergrowth shrubs of the outer coastal forest are salal, salmonberry and several species of genusVaccinium (eg, bilberries and huckleberries). These shrubs, notably salal, often form impenetrable thickets on exposed headlands. In the drier inner coastal areas, thimbleberry, red elderberry, Nootka rose, ocean spray, snowberry, western sword fern and deer fern are common in the undergrowth.

Specialized plant communities are associated with the beaches. Most are cobble or shingle beaches with a prominent driftwood zone containing large logs of the forest tree species. Fine sand beaches occur, most commonly in the southern portion of the Canadian Pacific coast. Common plants in the driftwood zone are American wild dune grass, beach pea, giant vetch, common cleavers, bluejoint small reed grass, tufted hair grass, Pacific coastal strawberry and sea plantain.

The Pacific coastline is highly dissected by many fjordlike inlets. Salt marsh vegetation is found at the head of such inlets. Common plants of these marshes are various species of alkali grass, seaside arrow grass, pickleweed, springbank clover, salt-marsh starwort and sedges such as Carex lyngbyei and C. obnupta. Grasses found in these communities are spike bent grass, red fescue, tufted hair grass and meadow barley. Occasional but conspicuous flowering plants include Douglas's aster, western buttercup, entire-leaved gumweed and Apargidium boreale. Soft rushes form conspicuous herbaceous clumps in these marsh lands.

Author: ROY L. TAYLOR

Cordillera

Vegetation of the Canadian Cordillera is very diverse. It ranges from alpine tundra to coastal rainforest to grasslands and savanna forests. In fact, 5 of the 8 major Canadian forest zones are found in the Cordillera.

Mountain systems typically have complex vegetation due to climatic effects of elevation and mountains as barriers to air flow. The Canadian Cordillera is no exception. Parallel bands of mountain ranges perpendicular to the easterly flow of weather systems creates many windward and leeward variations in vegetation. The climate gradients with elevation and latitude add to the vegetation variation.

The vegetation of the Cordillera is divided into 14 zones. Each zone has a characteristic zonal vegetation, soil and macroclimate. The zones, also called biogeoclimatic zones, are often found as elevation bands in the mountain systems, covering a narrow horizontal distance, but can cover extensive areas in the intermontane plateau areas. The 14 zones can be grouped into 7 regions.

Prairie Zones

Prairie is a natural grassland found in semiarid to subhumid climates. Plants are perennials, mostly grasses, associated with sedges, forbs (nongrasslike herbaceous plants) and a few dwarf shrubs. Before European settlement, uninterrupted grassland occupied almost all of southern Manitoba, Saskatchewan and Alberta, from Winnipeg to Calgary and from the US border to Saskatoon and Edmonton as well as the valleys of southern interior BC.

Grassland also occurred in the belt between this open grassland and the transition zone between this open grassland and the boreal forest to the north, where recurrent fires interfered with the development of trembling aspen groves that were scattered within the grassland after settlement. After settlement, shrubs and trees developed in sandy areas (eg, Great Sand Hills, Sask, and Carberry Sand Hills, Man) within the otherwise open grassland.

The nature of grassland vegetation depends on climate and soil. Precipitation increases eastward from the Rocky Mountains; temperature decreases northward. Both factors are affected by increasing elevation in the foothills of Alberta, on the valley slopes of BC and in elevated locations across the southern Canadian prairies.

Canadian grasslands are classified into 4 zones related to differences in climate, which also alters the nature of soils.

East of the mountains, the most extensive type is Mixed Prairie, so named because of the mixture of grasses of short- and midheight. This type occurs in the driest area (southwestern Saskatchewan and southeastern Alberta), where the topsoil is brown in colour and the dominant grasses (common spear grass, western wheat grass and blue grama) are relatively drought-resistant. Mixed Prairie also extends throughout the adjacent dark-brown soil zone (to the east, north and west), where less drought-resistant species (short-awned porcupine grass and northern wheat grass) prevail.

Fescue prairie occupies black soils in Alberta and western Saskatchewan between mixed prairie and the boreal forest, giving way eastward to the Tall-grass Prairie (also called true prairie) of southern Manitoba. The principal grass of Fescue Prairie is rough fescue; in Tall-grass Prairie, bluestems and porcupine grass are most important.

The grassland in BC is related to that of the Palouse Prairie of the states of Washington and Idaho. Bluebunch wheat grass is dominant in semiarid valley floors (lower grassland), with floristic changes through an intermediate type (middle grassland) to a type in which rough fescue is abundant (upper grassland).

Mixed Prairie and Tall-grass Prairie extend southward to Texas, with considerable change in species composition; Fescue Prairie and BC grassland (Palouse Prairie) extend southward into the adjacent states of the US.

Eastern Temperate Forests

The most northern expression of the extensive temperate forests of southeastern North America, this region is dominated by deciduous, broad-leaved trees. In favourable southern climates, deciduous leaves are most efficient, but they are energy-consuming because they must be renewed annually. A shorter growing season and harsher climate favour replacement by less efficient but less energy-demanding needle-leaved evergreens. Therefore, the zone may be divided into the Southern Deciduous forests and the more northerly Deciduous-Evergreen forests.

Atlantic Coastal Region

The vegetation of this region reflects also the human activity of the area. It has a rugged character with a marked contrast between the somber coniferous forests and mounds of brightly coloured wildflowers along roadsides during summer and autumn. The vegetation is a mosaic of natural human-altered and human-made habitats that is a product of glacial history and human colonization. This region is in the boreal forest, which has a forest dominated by conifers (spruce, pine, larch and fir); has been recently deglaciated; and has a humid climate and low elevations where wetlands develop.

Coastal Marine Flora

A Coastal Marine Flora comprises spermatophytes (flowering plants) and thallophytes (nonvascular, spore-producing plants, eg, algae and lichens) that live in or at the edge of the sea. The highly indented Canadian coastline provides many habitats for marine plants, from sheltered estuaries and lagoons to rocky shores exposed to open ocean.

The composition of the flora varies with habitat. Some algae and lichens live just within reach of wave spray; other algae occur as deep as sufficient light for photosynthesis penetrates (about 75 m on the Atlantic coast and slightly less in more turbid Pacific waters). Intertidally, plants are distributed according to resistance to temperature extremes, desiccation, strong illumination, and wave impact, and according to their ability to compete with other species for space.

In northern and eastern Canada, the capacity of plants to withstand ice cover and abrasion is a determinant of their distribution. Paradoxically, sheltered and shallow coastal waters in Canada may attain summer temperatures of 28° C or higher, and may support more southerly warm-water species that can tolerate cold winters.

Low Arctic

The Low Arctic is characterized by nearly complete plant cover and abundant low and dwarf woody shrubs. Major plant communities include tall (2-3 m) shrub tundra of alder, scrub birch and willows, along rivers, streams, steep slopes and lakeshores; low (30-60 cm) shrub tundra of willow, dwarf birch, dwarf heath shrubs, numerous sedges and small herbaceous species and abundant lichens and mosses, on medium-drained slopes; tussock sedge, dwarf heath shrubs, mosses and lichens on poorly drained soils of low rolling hills; and various combinations of sedges, a few grasses and herbs, and abundant mosses in poorly drained soils of flatlands where shallow lakes and low-centre polygons may occur.

These latter areas are the summer habitat of many waterfowl. Hills of tussock sedge and low shrub tundras are the summer rangelands of barren ground caribou and the year-round home of lemming, ptarmigan, fox and wolf.

High Arctic

In the High Arctic, vegetation is sparser and the wildlife it supports is more limited because of colder summers (2-5° C warmest month), shorter growing season (1.5-2.5 months), and low precipitation (100-200 mm). In lowlands, limited areas of sedge-moss tundras occur, decreasing in extent north of 74° N.

About 50% of the land cover consists of scattered clumps of dwarf prostrate shrubs (1-3 cm high) of willow and mountain avens, with small cushion plants (species of draba, saxifrage, chickweed, poppy), and abundant lichens and mosses; or areas of lichens, mosses, scattered clumps of grasses and rushes, and cushion plants. These lands (polar semideserts) can support small scattered herds of muskox and Peary's caribou, with waterfowl in lowland lakes.

At higher elevations (above 100 m) in the southern and central islands and at lower elevations in the more northerly islands, the abundance of surface stones of desert pavements, frost-shattered bedrock and small pockets of frost-churned fine soil result in truly barren land (polar deserts). Here flowering plants and mosses grow only where large snowbanks provide meltwater. Elsewhere, tiny scattered flowering plants grow with essentially no lichens or mosses.

Author: L.C. BLISS

Southern Subzones

The southern third is dominated by tall (15-25 m), semi-closed (40-60% cover) canopied forests composed of both pure and mixed stands of deciduous and coniferous trees. Aspen, balsam poplar and white spruce forests are common on upland sites in the western half; white and black spruce, balsam fir, aspen and paper birch are common east of Manitoba. In the area adjacent to the eastern temperate forest, red and eastern white pine, sugar and red maple and yellow birch also occur. Jack pine is a common species on coarse-textured, well-drained soils.

The middle portion of the Taiga has a greater abundance of coniferous trees than the southern third because of its colder climate. Upland sites are dominated by black and white spruce, jack pine and balsam fir. Warmer and drier sites are vegetated by aspen and paper birch.

The vegetation below forest canopies in the southern and middle portions of the Taiga is often composed of a mixture of herbs and deciduous shrubs. Cool site and older forest stands develop a carpet of feathermosses and have reduced abundances of other understory plants. In contrast, dry sites with open-growing (less than 30% cover) pines have a ground cover dominated by bearberry, blueberry and lichens. The climate and vegetation promote the development of Luvisolic soils on fine- to medium-textured sites; Podzols and Brunisols are common on coarse substrates.

Subarctic

The northern third to half of the Taiga, or Subarctic, has a shorter and colder climate than more southerly portions. These conditions result in open-growing stands of stunted (5-7 m tall) coniferous trees. Black spruce and balsam fir are the most common tree, but white spruce and paper birch do occur on warm dry sites. Between the dwarfed trees often occur shrubs such as dwarf birch and Labrador tea or mats of lichens and mosses. Brunisolic and Podzolic soils are commonly associated with upland sites. This portion of the Taiga is transitional to Arctic Tundra. Moose, black bear, snowshoe hare and in the northern portion, caribou are characteristic wildlife species of the Taiga.

Wetlands

Throughout the Taiga poorly and very poorly drained areas occur (probably at least 25% of total area), or wetland, filled with organic deposits (peatlands). These ecosystems are called fens or bogs depending upon whether they respectively are nutrient-rich or poor. Species such as black spruce, larch, eastern red cedar (eastern and southern portion only), willows, Labrador tea, bog rosemary, cloudberry, sedges, sphagnum and mosses are typical members of wetland communities.

Permafrost is commonly associated with peatlands, particularly the northern half of the Taiga. Major marshes, or wetlands without peat, can also be found in the Taiga. These include areas such as the large Peace-Athabasca delta in Wood Buffalo National Park. Sedges, horsetails and spike rushes are common plants in these areas.

Fires

Evidence of past fires is almost everywhere in the Taiga and many plants have mechanisms for surviving these catastrophic events. For example, many boreal plants can reproduce after disturbance by sprouting from understory stems including trees (aspen) and shrubs (saskatoon, willows, bearberry, rose) as well as some herbs. Some species have seeds which are easily dispersed by wind (birch, fireweed), while others have serotinus (ie, remaining closed) cones that protect seeds and open only after heating (jack pine, black spruce).

Natural processes allow the replacement of post-fire plant communities such as aspen and jack pine by more shade-tolerant trees (white and black spruce, balsam fir) when the interval between fires is long (eg, more than 150 years). This secondary succession can potentially result in climax vegetation.

Author: W.L. STRONG

Alpine Region

The Alpine region contains only the Alpine Tundra zone. This is a region of tundralike communities found at elevations above the treeline in mountain regions. It is a widespread zone in the Canadian Cordillera ranging through the Yukon, Mackenzie District of the NWT, BC and Alberta. The growing season is brief and frost can occur any time of year. Vegetation consists of mainly grasses, sedges, dwarf willows, mosses, lichens and other low woody and herbaceous plants. Lush herbaceous meadows can be found on moist areas at low elevations.

Pacific Coastal Subalpine Forest Region

This region contains only the Mountain Hemlock zone, which occurs at intermediate elevations in the Coast-Cascade and Vancouver Island mountains of BC. The area receives heavy snow cover and the soils do not freeze due to the thick insulating blanket of snow. Mountain hemlock, Pacific silver fir and yellow cypress are the characteristic tree species. Common understory plants include blueberries, copperbush, mountain heathers, rosy twisted stalk, oak fern and pipe cleaner moss. At the upper elevations of the zone a parkland area of conifers and meadows or heaths usually occurs.

Interior Cordilleran Subalpine Forest Region

This is the subalpine region further inland from the coast. In this region, the ground usually freezes before the snow falls. Two zones are recognized. The first, the Engelmann Spruce-Subalpine Fir zone, occurs commonly in BC and Alberta. Typical tree species include Engelmann spruce, subalpine fir, lodgepole and whitebark pines and subalpine larch. Common understory plants are white-flowered rhododendron, false azalea, black huckleberry, Sitka alder, oak fern, mountain arnica and leafy liverwort.

The second zone, the Spruce-Willow-Birch, is found in northern BC and Alberta (Cariboo Mountains), the Yukon and Mackenzie District of the NWT. White spruce is common throughout and subalpine fir is common in BC and the southern Yukon. Lodgepole pine occurs on disturbed or dry sites and black spruce is frequent at lower elevations. Common shrubs are willows and scrub birch. Common herbs are Altai fescue, Labrador lousewort and arctic lupine. Step moss is also abundant. Shrub-dominated vegetation is very common at upper elevations and in wide valleys influenced by cold air drainage.

Boreal Montane Forest Region

This region comprises 3 zones. All are characterized by a strongly continental climate (ie, warm summers and severe winters) and are found at montane elevations (ie, below the subalpine), commonly on intermontane plateaus. The first is the Boreal White and Black Spruce zone. This is equivalent to the boreal coniferous forest of much of the rest of Canada, but in the Cordillera it is the zone found in the mountain valleys of Alberta, northern BC, Yukon and the NWT, where it is generally on better drained soils. Permafrost is uncommon in BC and Alberta Cordillera but is more frequent northward.

Forests are primarily mixes of white and black spruce, lodgepole pine, balsam poplar, paper birch and trembling aspen. Common understory plants include mountain and green alders, highbush cranberry, wild rose, Canadian buffaloberry, fireweed, Canada reed grass, lingonberry, twinflower and feathermosses.

The Sub-Boreal Spruce zone is found in BC in the central plateau between the Coast and Cariboo-Rocky Mountains. It has slightly cooler summers due to more cloud cover and shorter lengths of days and less severe winters with more snow than the Boreal White and Black Spruce zone. The forests are dominated by hybrid white spruce (Engelmann x white), subalpine fir, lodgepole pine, Douglas fir, black spruce and black cottonwood with some trembling aspen and paper birch forests, particularly where there are lots of fires.

Common shrubs are black huckleberry, Sitka alder, birch-leaved spirea, falsebox, black twinberry, thimbleberry and devil's club. Lily species, such as false Solomon's seal, twisted stalk, fairybells and Queen's cup are common in the understory along with oak fern, foamflowers, palmate coltsfoot and feathermosses.

The third zone is the Sub-Boreal Pine-Spruce. It is found in the Chilcotin Plateau area of central BC. The climate of this high plateau is similar to the Boreal White and Black Spruce zone with severe winters and warm, dry summers. Pine forests dominate the landscape due to common fires. Hybrid white spruce is also common and there is frequent trembling aspen and black spruce. Common understory plants are Canadian buffaloberry, juniper, dwarf blueberry, pine grass, kinnikinnick, crowberry, red-stemmed feathermoss and many lichens.

Cordilleran Montane Temperate Forest Region

This region includes 3 zones. The first is the Interior Cedar-Hemlock zone. This zone is found in warm, moist to wet valleys throughout southeastern BC and on the leeward side of the Coast Mountains in northwestern BC. It is the wettest and most productive zone in the BC interior.

Western red cedar and western hemlock are the dominant tree species, but many others can also occur in this zone, including Douglas fir, lodgepole and western white pines, hybrid white spruce, subalpine fir, western larch, paper birch and trembling aspen. In areas with ample precipitation, western hemlock and red cedar forests as magnificent as the coastal rainforests are found. These forests are called ancient, as they are close to a thousand years old.

Understory plants vary quite a bit over the range of this zone but include red twinberry, falsebox and tall Oregon grape in the south, and black huckleberry and Sitka mountain ash in the north. Devil's club, oak fern, Queen's cup, rosy twisted stalk, skunk cabbage and feathermosses are common throughout.

The second zone is the Interior Douglas Fir. It is found at lower elevations on the eastern slopes of the Rocky Mountains in Alberta, intermediate elevations in southern BC mountains, and dominates the vegetation of the southern intermontane plateaus of BC. This is a warm, continental zone dominated by Douglas fir with several other trees species commonly present such as lodgepole and ponderosa pines, hybrid white spruce, western larch, paper birch, black cottonwood and trembling aspen. Western red cedar is found abundantly in wetter parts of the zone.

Pine grass is the dominant and characteristic plant of the understory. Other widespread plants are Rocky Mountain and common junipers, birch-leaved spirea, saskatoon, bluebunch wheat grass, kinnikinnick and twinflower. Grasslands dominated by bluebunch wheat grass, fescue, and in some instances needle grass are common in some parts of this zone. There are also many parkland areas with a mix of forest and grassland.

The Montane Spruce zone is found at elevations between the Interior Douglas Fir and Engelmann Spruce-Subalpine Fir zones throughout most of its range in southern BC and the east slopes of the Rocky Mountains but is also found above the Sub-Boreal Pine-Spruce zone in central BC. In many ways, the climate is similar to dry to moist parts of the Sub-Boreal Spruce zone: warm summers and cold, but not severe winters.

Lodgepole pine dominates the forest cover due to common wildfires. Engelmann and hybrid white spruce are usually in the understory and dominate stands that have escaped fires for some time. Plants such as falsebox, grouseberry, pine grass, twinflower, wintergreen and red-stemmed feathermoss are often found under the trees.

Cordilleran Cold Steppe and Savanna Region

This region includes dry climate zones where significant moisture deficits occur in the soils. There are 2 zones, both in BC. The first is the Bunchgrass zone. This is a grassland zone dominated by big sagebrush and bluebunch wheat grass. Other common species are rabbitbrush, pasture sage, june grass and prickly pear cactus. A surface crust of lichens and mosses between the clumps of grass indicates grasslands in excellent condition; these are infrequent due to grazing by cattle.

This is the warmest and driest zone in the Cordillera and is found primarily in the bottom of the deep valleys of the southern interior in an area of strong rain shadow from the Coast Mountains. The zone is the northernmost extension of the Columbia Basin grasslands of the US.

The Ponderosa Pine zone is found at elevations between the Bunchgrass zone and the Interior Douglas Fir zone in these dry parts of BC. Forests are dominated by ponderosa pine, with the most common understory plants being bluebunch wheat grass and fescues. Forests are both open, savannalike and closed. Bluebunch wheat grass grasslands are often intermixed with small patches of ponderosa pine forest. Other typical species are arrow-leaved balsamroot, yarrow and pussytoes. Douglas fir is found on wetter sites and where fires have been prevented. Forests on wetter sites can also be dominated by trembling aspen, cottonwood and paper or water birches.

Pacific Coastal Mesothermal Forest Region

This region consists of 2 zones characterized by a mild coastal climate. The first, and the drier of the 2, is the Coastal Douglas Fir zone. It is found mainly in the Pacific coastal region on Vancouver Island and is only a minor type in the Cordillera of the western mainland coast.

The vegetation is dominated by forests of Douglas fir although other common tree species are arbutus, western flowering dogwood, bigleaf maple, grand fir and western red cedar. The Garry oak meadow vegetation is very colourful in the spring with abundant wildfowers. Coniferous forests have an understory of Indian plum, ocean spray, western snowberry, dull Oregon grape, honeysuckles and salal.

The Coastal Western Hemlock zone is also commonly referred to as temperate rainforest. The climate is wet and warm and the forests of this zone are the most productive and majestic in Canada. It occurs all along the coast of BC and the valleys of the Coast Mountains. These rainforests are characterized by western hemlock, western red cedar, Pacific silver fir, Sitka spruce and Douglas fir. Other common tree species are yellow cypress, grand fir, red alder, black cottonwood and shore pine. The understory plants are varied and include Alaskan blueberry, red huckleberry, salmonberry, salal, devil's club, deer fern, sword fern, skunk cabbage and lanky moss.

Author: D. MEIDINGER

Species Composition

In the black soil zone, forest penetrates prairie where the local climate is moister and cooler than average (north-facing slopes, edges of sloughs and elevated areas), so that grassland and forest intermingle to form the aspen grove region within Fescue Prairie and Tall-grass Prairie. In BC, the margin between open grassland and forest is a savanna (grassland with scattered trees) with Douglas fir as the main tree.

The character of grassland varies locally with soil texture. In dune sand, various specialized grasses abound (eg, sand grass, sand dropseed and Indian rice grass). In saline flats, salt grass, alkali grass and wild barley dominate. Similarly, the wet slough environment results in a cover of various grass species (eg, slough grass, spangle top, bluegrasses), sedges, bulrushes and cattail. Usually, 2-3 grass species contribute 70% or more of the vegetation; the number of associated species varies widely, diversity increasing with moistness of habitat. Usually, 2-3 perennial grass species contribute 70% or more of the herbage; the number of associated species varies widely, diversity increasing with moistness of habitat. Although the amount of plant biomass produced in natural grassland is similar to that in annual cropland, half or more of it is of underground parts.

The growth pattern is very conservative, with leaves developing from April to October but each remaining in the canopy through only part of the growing season. As a result, the maximum herbage yield in midsummer is only one-third or less of the annual herbage production. The proportion of herbage that is consumed by animals (birds, mice, voles, invertebrates) is very small. Estimates indicate that livestock consume less than 10% of herbage production in moderately grazed grassland. The major part of the herbage becomes a protective layer of litter on the soil surface, which together with the underground plant parts (stems and roots) passes through the decomposer food chain through activities of micro-organisms (mostly fungi and bacteria) and invertebrates (particularly nematodes).

Disappearing Prairie

At the end of the 19th century, rangeland grazing by domesticated livestock was the principal agricultural use made of the prairies. The cultivated area increased rapidly 1900-30; today, about 55% of the area east of the mountains is under crop or summerfallow, representing 65% of cultivated land in Canada. The high fertility of prairie soils is depleted by tillage. Estimates indicate that a third to half of organic matter in cultivated prairie soils has been lost (see Soil Conversion). In natural grassland a much smaller proportion of the soil nutrients is in a form readily available for plant growth - or for loss by volatilization to the atmosphere or to the subsoil by leaching. The grassland that remains uncultivated is mostly unsuited as cropland because of steepness of slope, sandiness, stoniness, salinity, aridity or lack of drainage. Much of this is in community pastures or crown land leased by ranchers. Most of the vegetation has been altered by overgrazing; this results in a relative increase in certain species ("increasers," eg, blue grama grass, dwarf sedges and pasture sage) and a relative decrease in others ("decreasers," eg, spear grasses and wheat grasses). The Grasslands National Park reserve, Saskatchewan, was established to ensure survival of some native prairie.

Author: ROBERT T. COUPLAND

Southern Deciduous Forests

The summer green character is most prominent in extreme southern Ontario, where 80 different tree species grow naturally (now largely displaced by agriculture). Within this region, many dominance patterns occur because of local variations in soil moisture, soil type and microclimate. In drier environments of the Southern Deciduous forests, black, red and white oak predominate and shagbark hickory, hop hornbeam, beech, red maple and white pine are strong associates.

In mesic (moist) environments, sugar maple and beech dominate in association with red elm, black maple, black cherry, white ash and basswood. In wet lowlands and bottomlands, white elm and red and silver maple are major forest components, growing with black walnut, white and green ash, bitternut hickory, cottonwood, pin oak, box elder and black willow.

In Canada, many southern species occur only in this region (eg, flowering dogwood, chestnut and Hill's oaks, sweet pignut, pignut and kingnut hickories, sweet chestnut, red mulberry, sassafras, tuliptree, Kentucky coffee tree, hackberry, cucumber magnolia, sycamore, sour gum and honey locust). White pine and pencil cedar are associated evergreens in dry environments; hemlock is the only other significant conifer in moist forests. Left undisturbed, the trees in these forests grow to great size (40 m) and great age (500 years).

Deciduous-Evergreen Forests

These forests are often referred to as mixed forests; however, pure evergreen or deciduous types are also prevalent. Thus, in the broad triangle from Michipicoten to North Bay, Ont, and Ste-Agathe, Qué, with outliers west of Thunder Bay, at Lac Saint-Jean and in the Gaspé Peninsula, the drier sites support forests of jack pine, red or white pine in association with large-tooth aspen, red oak, beech, paper birch, trembling aspen and hemlock.

Moist forests are composed of sugar maple as an almost overriding dominant or in association with beech (south), basswood, hop hornbeam, yellow birch or hemlock. These terminal forests are remarkably similar to those on mesic sites southward. Wet environments support monodominant forests or admixtures of white elm, silver maple (southward), red maple (northward), white cedar or black willow. Associated species include green and black ashes and larch.

Northward, evergreen elements are more dominant. Stands of pine, white cedar, larch and, occasionally, black spruce become prominent parts of the forest scene. Successional forests are also frequent. Extensive stands, often of a single species (eg, trembling aspen, paper birch, jack, red or white pines), result from frequent fires. Trees are frequently short-lived and vulnerable to wind, disease and fungus attack. Except for white and red pine and maple, the forests seldom achieve great age or size.

Understory

In summer, deciduous forests are too shady for growth of significant ground cover; however, in spring, flowering plants with short reproductive cycles are abundant. These wildflowers provide welcome contrast to the monotony of winter snow and the sombre majesty of the mature forests, but far more spectacular is the brilliant display of colour before leaf-fall.

Author: PAUL F. MAYCOCK

Forests

The island of Newfoundland lies at the eastern limits of the Boreal Forest Region. The island's forests are dominated by conifers, particularly white and black spruce and balsam fir. The Maritime provinces have red spruce as the dominant species. Deciduous species are intermixed with birch and popular in Newfoundland and maple, beech and oak in the inland valleys of the maritimes. The diversity of species in the forest has been reduced by clearing and fires and unless they are maintained, the cleared or burnt-over areas are recolonized by stands of white spruce and balsam fir. Such relatively pure stands have been plagued by problems common to monoculture situations such as insect attacks, in this case by the spruce budworm.

Wetlands and Heaths

Wind, cool temperatures and abundant precipitation are characteristic of the maritime climate. Along sea coasts, forests are usually dwarfed and large areas of peatland and heath occur, particularly in Nova Scotia and Newfoundland. Peatlands are areas of poor drainage and low productivity dominated by sphagnum, sedges, heath shrubs, stunted black spruce and larch.

Heaths are found along the coasts, on hilltops and in other areas where forests have difficulty becoming established. They are areas of short, shrubby vegetation which are usually dominated by crowberry, bilberries, dwarf birches, junipers and other dwarf or prostrate shrubs.

There are some saltmarshes and freshwater marshes, particularly in the Bay of Fundy area.

Inland Areas

Forest growth improves in inland valleys and in many parts of New Brunswick because of better soils and more protected situations. However, the woodland flora is less rich than it is farther south. The growth of blueberries, an important crop of the region, is promoted by controlled burning which reduces competition from other species and keeps the blueberry plants pruned, thus ensuring young production growth.

Author: PETER J. SCOTT

Flowering Flora

In Canada, marine flowering plants may be dune and beach-dwellers adapted to a dry habitat (eg, sea rocket), saltmarsh species tolerant of periodic flooding by tides (eg, cordgrass) or truly marine and usually submerged sea "grasses" (eg, eelgrass and surf-grass).

Spore-producing Flora

Marine spore-producing plants are much more numerous, the most conspicuous and diverse being benthic (attached to substratum) algae. They range from microscopic single cells and plantlets to some of the tallest organisms known. Most are grouped into 3 main colour classes: red, brown and green. A fourth group, Cyanobacteria (or blue-green algae), is widespread and often abundant; however, it consists chiefly of microscopic forms and is usually poorly documented because of taxonomic difficulties.

Algal Flora

The richest Canadian marine algal flora occurs on the Pacific coast, where about 625 species are recognized (58% red, 23% brown, 18% green, 1% other) from BC and adjacent American shores. This profusion is due mainly to equable ocean temperatures and the upwelling of nutrient-rich water. The diversity is at times spectacular, as in the 17 genera of kelps, some of which may exceed 30 m in length.

In Atlantic Canada, with cold Arctic currents and severe winter conditions, a markedly different and less diverse algal flora of about 340 species occurs (37% red, 35% brown, 26% green, 2% other). With fewer species present, some can exist in greater number and densities and exposed Atlantic shores usually show striking vertical zonation of a few dominant algae. Production (conversion of inorganic carbon to plant tissue) in some of these dense seaweed communities exceeds that of many other marine and terrestrial ecosystems. About 128 species are common to both Atlantic and Pacific shores.

The Canadian Arctic, with low temperatures and limited sunlight, has a meagre algal flora of 170 species (32% red, 38% brown, 30% green). Arctic algae appear to be peculiarly adapted to photosynthesize with minimal light and temperature, although heterotrophy (by absorption and metabolism of organic substances dissolved in sea water) has been suggested as a means of subsistence. Incidence of annual species decreases at higher latitudes, and the intertidal flora is sparse or absent.

Author: C.J. BIRD