There is virtually no agriculture possible, but mineral exploration and exploitation have had some effect. Selwyn Lake Upland: This ecoregion is found in the extreme northeast. The relief is low, and the landscape is dominated by moraines and till plains. The area is drained by the Churchill and Nelson rivers. Tazin Lake Upland: An area of higher relief than the Selwyn Lake Uplands, where moraines are less well developed and the surface is often bare rock outcrops.
There are black spruce-jack pine forests with a more specious vegetation, reflecting the somewhat less harsh climate. The ecodistricts, differing in relief and soil development, are: Uranium City Upland and Territories Upland. Boreal Shield: This largest ecozone, which at Bedrock alternates with glacial tills; as in the Taiga, glaciation resulted in a rolling topography containing numerous lakes of various sizes.
The climax vegetation of much of the region is dense black spruce with moss ground cover. In more protected and open areas, there are birch and trembling and balsam poplar, as well as jack pine and tamarack. This more diverse vegetation supports a larger fauna than further north. Several species of the deer family as well as a number of carnivores such as wolf, marten and mink, are residents.
Bird such as ravens, barred owls and boreal chickadees are also to be found, while a large number of insectivorous birds are summer residents, raising their young on the numerous insects of the short summer. This region has been the site of extensive mining.
The landscape is a patchwork of glacial and waterborne deposition, with moraines, eskers and sand dunes resulting from erosion of the underlying sandstone. Churchill River Upland: Based on Precambrian crystalline bedrock, this is the eastern section of the ecoregion. It is the largest single ecoregion of the province; at The area has a thinner glacial deposit and less soil development than the softer rock of the Athabasca Plain.
The lack of erosion materials leads to the clear water of the lakes and their lower productivity. Boreal Plain: The Boreal Plain is an area of rolling plain based on sedimentary rock and covered by thick glacial deposits, interspersed by lakes and glacial kettles. The warmer climate of the ecozone, in relation to those further north, supports a greater variety of vegetation.
The forest is mixed hardwood and coniferous species that include white and black spruce, jack pine, aspen, white birch, and balsam poplar. Lowlands near water may have American elm, green ash, and willows and sedges, along with a variety of flowering plants. Bird species richness is also high, with a number of migrants breeding in the area.
Human activities in the region include forest-based hunting, fishing, trapping, and logging. The distribution of biomes is determined by environmental conditions, which must be appropriate to support the dominant species. Moisture and temperature are usually the most important environmental influences on the distribution of terrestrial biomes Figure 8. The distribution of various types of wetlands within terrestrial biomes is mostly influenced by the amount and permanence of surface water and the availability of nutrients.
Marine biomes are most strongly influenced by water depth and upwellings, which affect the amounts of light and nutrients that are available to support primary productivity. Distribution of the Major Terrestrial Biomes. Note that the spatial complexity is greatest in regions with mountainous terrain, such as the western Americas and southern Asia.
Source: Modified from Odum Environmental Influences on the Distribution of Terrestrial Biomes. This diagram suggests the reasons why temperature and moisture are believed to be the most important environmental factors affecting the distributions of terrestrial biomes. As long as environmental conditions are suitable for its development, a particular biomes may occur in widely divergent regions, even on different continents. Although widely separate regions of a biome may be dominated by different species, their life forms are typically convergent.
In other words, the different species are comparable in their form and function, because the regimes of natural selection occurring in similar environments result in parallel or convergent evolutionary responses. Therefore, biomes are defined primarily by the structure and function of their ecosystem, but not necessarily their species composition.
This context is illustrated by the boreal forest, an extensive biome that occurs in northern regions of Canada, Alaska, and Eurasia. The boreal forest occurs in regions with a cold and long winter, short but warm summer, and generally moist soil. This biome is situated between the more northern tundra, and temperate forest or prairie to the south. The dominant vegetation of boreal forest is typically coniferous trees, especially species of fir, larch, pine, or spruce.
However, the particular species vary from region to region, and angiosperm hardwood trees may also be present. Over much of northern Canada the boreal coniferous forest is dominated by stands of black spruce Picea mariana.
However, in some regions, stands of white spruce Picea glauca , jack pine Pinus banksiana , balsam fir Abies balsamea , or tamarack Larix laricina are dominant. In the boreal forest of northern Europe, Siberia, and northern parts of Japan, Korea, and China, there are other species of coniferous trees.
In some cases, there may be stands dominated by hardwood trees, such as trembling aspen Populus tremuloides in parts of northern Canada. However, all of these different forest types occurring on several continents are structurally and functionally convergent ecosystems within the same biome—the coniferous forest. We should also note that any particular biome is described on the basis of its dominant, most extensive kind of ecological communities.
For the boreal forest, this is usually stands of coniferous trees. However, biomes are not homogeneous, and they contain other kinds of less-widespread communities. For instance, parts of the boreal forest are dominated by persistent areas of shrubs such as species of alder, dwarf birch, and willow, and there may also be wetlands such as bogs and fens as well as distinctive communities associated with streams and rivers.
In addition, local areas may be subjected to occasional catastrophic disturbances, which may result in a landscape being composed of a mosaic of stands of various stages and ages of ecological recovery, called succession. In the case of boreal forest, disturbances are typically caused by wildfire or by epidemics of insects that kill trees see Chapter Natural biomes are characterized by their dominant ecological communities, which are composed of particular assemblages of plants, animals, and microorganisms.
There are also anthropogenic ecosystems that are strongly influenced by humans and their activities, such as cities and agricultural land. In fact, all of the modern biomes have been influenced by people to some degree—at the very least, all organisms in even the most remote places now contain trace contaminations of organochlorine chemicals such as DDT and PCBs that humans have manufactured and dispersed into the environment see Chapter Ecologists have used a number of systems to divide the biosphere into major biomes, one of which is illustrated in Figure 8.
The classification of global biomes described here is modified from a system proposed by the ecologist E. This is appropriate because biomes are widespread ecological units whose boundaries and species do not respect political boundaries. Tundra is a treeless biome that occurs in environments with a long, cold winter and a short, cool growing season.
There are two types of tundra: alpine and arctic. Alpine tundra occurs at higher elevations in mountainous regions, even in tropical countries. Arctic tundra occurs at high latitudes—that is, in northern regions of the Northern Hemisphere and southern parts of the Southern Hemisphere.
Most tundras are a meteorological desert because they receive sparse precipitation. Nevertheless, the soil may be moist or wet because the cold environment restricts the amount of evaporation that occurs, and frozen soil may prevent deep drainage of water. The coldest, most northerly, high-Arctic tundra is extremely unproductive and dominated by short, long-lived plants, generally growing less than cm above the surface. In the less-cold environments of the lower Arctic, well-drained tundra may be dominated by shrubs growing as tall as m, while wetter habitats support productive meadows of sedge, cottongrass, and grass.
Image 8. Tundra is a biome of short vegetation growing in climatically stressed environments of the Arctic and Antarctic and on mountaintops. This is a view of arctic tundra on northeastern Somerset Island. The initials E. Source: B. Boreal coniferous forest, or taiga, is an extensive biome of environments with a cold winter, short but warm growing season, and moist soil.
It is most extensive in the Northern Hemisphere. The boreal forest is dominated by coniferous trees, especially species of fir, larch, pine, and spruce. Some angiosperm trees may also be prominent, particularly aspen, birch, and poplar. Stands of boreal forest are poor in tree species, and may be dominated by only one or a few kinds. Most regions of boreal forest are subject to periodic disturbances, usually by wildfire, but sometimes by windstorms or insect epidemics.
The boreal coniferous forest taiga is extensive in northern regions of Canada, Alaska, and Eurasia. This photo shows a stand of black spruce with a carpet of feather mosses, in central Labrador. Montane forest occurs at sub-alpine altitudes on mountains in temperate latitudes. It is similar in structure to high-latitude boreal forest and is also dominated by conifers.
Temperate deciduous forest occurs in relatively moist, temperate climates with a short, moderately cold winter and warm summer. This biome is dominated by a mixture of hardwood tree species. Most of the trees have seasonally deciduous foliage, meaning their leaves are shed each autumn and then regrown in the springtime. This is an adaptation to surviving the drought and other stresses of winter.
Common trees of temperate deciduous forest in North America are species of ash, basswood, birch, cherry, chestnut, dogwood, elm, hickory, magnolia, maple, oak, sassafras, tulip-tree, and walnut. These trees occur in distinctive communities based on their preferences for particular qualities of soil moisture and fertility, soil and air temperature, and other environmental factors.
The temperate deciduous forest contains species of angiosperm trees, which drop their leaves in the autumn, plus some coniferous trees. This biome is widespread south of the boreal forest. This stand in Nova Scotia is dominated by birches, maples, and white spruce.
Temperate rainforest develops in a climate in which the winter is mild and precipitation abundant year-round. Because this climate is too moist to allow frequent wildfires, old-growth forest often develops. The old-growth forest is dominated by coniferous trees of mixed age and species composition, but some individual trees are extremely large and can be centuries old, sometimes even exceeding a thousand years.
Prominent tree species in temperate rainforest of the humid west coast of North America are Douglas-fir, hemlock, red cedar, redwood, Sitka spruce, and yellow cypress.
Under these conditions, soil moisture is adequate to prevent desert from developing, but insufficient to support forest. Temperate grassland is called prairie in North America and steppe in Eurasia, and this biome occupies vast regions in the interiors of both continents. Prairie is commonly divided into three types according to the height of the dominant vegetation: tall-grass, mixed-grass, and short-grass.
Tall-grass prairie is dominated by various grasses and herbaceous angiosperm plants, such as blazing stars and sunflowers, some as tall as m. Fire is an important factor that prevents tall-grass prairie from developing into an open forest. Tall-grass prairie is a critically endangered ecosystem because almost all of it has been converted into agricultural land.
Mixed-grass prairie occurs where there is less rainfall and the habitat is characterized by shorter species of grasses and herbaceous angiosperms. Short-grass prairie develops where precipitation is even less, and it can be subject to unpredictable, severe drought. Temperate grassland is widespread in the dry interior of North America and other continents, and is dominated by species of grasses and other herbaceous plants.
This view is of shortgrass prairie in Grasslands National Park in southern Saskatchewan. Chaparral develops in south-temperate environments with a so-called Mediterranean climate, with winter rains and summer drought.
Typical chaparral is characterized by dwarfed trees and shrubs with interspersed herbaceous vegetation. Periodic fires are characteristic. In North America, chaparral is best developed in coastal southern California.
Desert can be temperate or tropical, and it most commonly occurs in continental interiors or in the rain shadow of mountains.
The distribution of desert is determined by the amount of soil moisture, which in the temperate zones is generally associated with an annual precipitation of less than about 25 cm. The driest desert supports almost no plant productivity, but less-dry conditions may support communities of herbaceous and succulent plants, both annual and perennial.
Occasional moist places with springs of groundwater develop a relatively lush vegetation of shrubs or trees and are known as oases. Desert is a sparsely vegetated biome of extremely dry environments.
This view is of arid habitat in Peru, in a region where there is no detectable precipitation in some years. Tropical grassland and savannah occur in regions with as much as cm of annual rainfall, but a pronounced dry season. Savannah is dominated by grasses and herbaceous angiosperms, with scattered shrubs and tree-sized plants that provide an open canopy.
Some tropical grasslands and savannahs support large populations of big animals, including migratory ones. Grasslands occupy most of the eco-regions of the earth and they contain several grass species such as sedge, rush, and legumes such as clover and other herbs. The biodiversity of flora, fauna and ecosystems that characterise an ecoregion tends to be distinct from that of other ecoregions. In theory, biodiversity or conservation ecoregions are relatively large areas of land or water where the probability of encountering different species and communities at any given point remains relatively constant, within an acceptable range of variation largely undefined at this point.
Ecoregions are identified by analyzing the patterns and composition of biotic and abiotic phenomena that affect or reflect differences in ecosystem quality and integrity Omernik , These phenomena include geology, landforms, soils, vegetation, climate, land use, wildlife, and hydrology.
The community is a part of the ecosystem only, which consist of populations of different types of species together. What are the factors that determine an ecozone boundary? What is the main factor that separates the biomes? Which biome is most sustainable? Which biomes have the most species? Why do we need to manage biomes in a sustainable way? Which biomes are most affected by humans and why? Is it possible for a biome to change from one type to another?
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