Environmental Change Ch. 6.docx

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University of Toronto St. George
School of Environment
Simon Appolloni

Environmental Change Chapter 6- Ecosystems in the Environment - similar climactic conditions are repeated in different geographical areas and result in similar assemblages of biological organisms, known as biomes - Biomes are defined as having climactically and geographically similar conditions that result in certain communities of plants, animals, and soil organisms - Unlike ecozones, biomes are not defined by genetic, taxonomic or historical similarities - Each biome has a characteristic assemblage of plants and animals that have adapted and evolved to these climactic conditions - Near the poles, temperature is generally the overriding climate factor defining a biome, whereas in temperate and tropical regions, precipitation is more significant than temperature - Canada’s terrestrial land base has been classified into biomes using the Canadian Committee on Ecological Land Classification System as developed by Natural Resources Canada Tundra - Tundra occurs in the extreme northern latitudes where the snow melts seasonally - The southern hemisphere has no equivalent of the arctic tundra because it has no land in the corresponding latitudes - A similar ecosystem located in the higher elevations of mountains, above the tree line is called alpine tundra - Most tundra soils formed when glaciers began retreating after the last ice age, about 17,000 years ago - These soils are usually nutrient poor and have little detritus - Although the tundra’s surface soil that’s during summer, beneath it lies a layer of permafrost, permanently frozen ground that varies in depth and thickness - Tundra supports relatively few species that do occur there often exist in great numbers - Animals adapted to live year-round in the tundra include polar bears, lemmings, voles, weasels, arctic foxes, snowshoe hares, ptarmigan, snowy owls, and muskox - Tundra recovers slowly from even small disturbances - Oil and natural gas exploration and development and military use have caused damage to tundra likely to persist for hundreds of years Boreal Forest - Just south of the tundra is the boreal forest, or northern coniferous forest, which stretches across North America and Eurasia - There is no biokme comparable to the boreal foest in the southern hemisphere - Winters are extremely cold and severe, although not as harsh as those in the tundra - Boreal forest receives little precipitation and its soil is typically acidic and mineral poor, with a thick surface layer of partly decomposed pine and spruce needles - Where permafrost occurs, it is found deep under the surface - Conifers have many drought resistant adaptions, such as needle-like leaves whose minimal surface area prevents water loss by evaporation - Being evergreen, conifers resume photosynthesis as soon as warmer temperatures return - The animal life of the boreal forest consists of some larger species such as caribou, wolves, brown and black bears and moose - Currently, boreal forest is the world’s top source of industrial wood and wood fibre Temperate Rainforest - A coniferous temperate rainforest, known as coast forest in the CCELC system, occurs on the northwest coast of North America - Annual precipitation is high - The proximity of temperate rainforest to the coastline moderates its temperature so that the seasonal fluctuation is narrow; winters are mils and summers are cool - Temperate rainforest has relatively nutrient-poor soil, though its organic content may be high - The dominant vegetation in the North American temperate rainforest is large evergreen tress such as western hemlock, Douglas fir western red cedar Temperate Deciduous Forest - Hot summers and cold winters characterize the temperate deciduous forest - Typically, the soil of a temperate deciduous forest consists of a topsoil rich in oganic material and a deep clay-rich lower layer - The trees of the temperate deciduous forest form a dense canopy that overlies saplings and shrubs - They originally conatin a variety of large mammals, such as puma, wolves and bison, deer, and bears - Logging and land clearing for farms, tree plantations and cities destroyed much of the original temperate deciduous forest Temperate Grassland - Summers are hot, winters are cold and rainfall is often uncertain - Average annual precipitation ranges from 25-75 cm - Grassland soil has considerable organic material because the aboveground portions of many grasses die off each winter and contribute to the organic content of the soil - Moist temperate grasslands have largely disappeared from the Canadian prairies except in preserved locations in Manitoba - Trees grow sparsely except near rivers and streams, but grasses taller than a person grow in great profusion in the deep, rich soil - Periodic grazing, and wildfires have helped to maintain grasses as the dominant vegetation in grasslands - More than 90 percent of the North American grassland encountered by European settlers has been converted to farmland, and the remaining prairie is highly fragmented - Short grass prairies are temperate grasslands that receive less precipitation than moist temperate grasslands but more precipitation than deserts - Grasses that grow knew high or lower dominate short grass prairies - Mixed grass prairies are positioned between the tall and short grass prairies and are dependent on an intermediate precipitation regime - The mixed grass prairie is an important faunal boundary Tropical Rainforest - Tropical rainforest occurs where temperatures are warm throughout the year and precipitation occurs almost daily - Therefore, we do not find these biomes in the northern hemisphere - Due to their extremely important contribution to biodiversity and global carbon uptake, they deserve recognition in our discussion - These forests are found in places
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