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Biology 2F03.pdf

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McMaster University
Jurek Kolasa

Biology 2F03 Fundamental and Applied Ecology Chapter 2 Life on Land 21 LargeScale Patterns of Climatic VariationUneven heating of the earths spherical surface by the sun and the tilt of the earth on its axis combine to produce predictable latitudinal variation in climateTemperature precipitation and atmospheric circulation Because the earth is a sphere the suns rays are most concentratedwhere the sun is directly overhead which changes with seasonsoEarths axis is tilted approximately 235 away from the perpendicularstJune 21 during summer solstice the sun is directly overhead at theotropic of Cancer 235 N latitudestDecember 21 during winter solstice sun is directly overhead atotropic of Capricorn 235S latitudeSun is directly over the equator during the spring and autumnalrdstand September 23equinoxes On March 21 Heating of the earths surface and atmosphere drives circulation of theatmosphere and influences patterns of precipitationoAir moving from 30 latitude back to the equator completes a thermalloop which forms the Hadley celloPolar cell driven by ait movement associated with warming at 60latitude and cooling at the polesFerrel cells occurs at midlatitudes and is driven in part by the effectsPolar cellsof the Hadley and Prevailing winds do not move in a straight northsouth directionbecause of the Coriolis effect Climate diagrams Tool to explore the relationship between the distribution of terrestrialvegetation and climateSummarize climatic information including seasonal variation intemperature and precipitation length and intensity of wet and dryseasons and the portion of the year during which average minimumotemperature is above and below 0CWhen the temperature line lies above the precipitation line potentialevaporation rate exceeds precipitation dry periodsAlso include mean annual temperature precipitation and theelevation of each site above sea level22 Soil Foundations of Terrestrial BiomesSoil structure from the longterm interaction of climate organisms topography and parent mineral materialO horizons found in soils in which the plant material is primarily aquatic in natureLFH horizons found in more upland sitesSmall organic horizons are found in areas with little litter decomposition or high decomposition ratesDeep organic horizons are found in areas with substantial little inputs andor low decomposition ratesA horizon contains a mixture of mineral materials clay silt and sand as well as organic material derived from the organic horizon aboveB horizon contains the materials leached from above often resulting in a distinctive banding patternC horizon consisting of weathered parent material broken down through the actions of frost water microbial activity and deep penetrating rootsUnder the C horizon we fin unweathered parent material which is often bedrockPlants secrete numerous root exudates which along with the living roots and plant litter serve as substrates for bacterial fungal and animal speciesGrowth and activity of organisms provides stability to the mineral components of the soil allowing development and maintenance of complex canals of air spaces and cavities within the soilClimate affects the rate of weathering parent materials leaching of organic and inorganic substances erosion and decomposition of organic matter through direct weathering effects 23 Natural History and Geography of BiomesThe geographic distribution of terrestrial biomes correspond closely to variation in climate especially prevailing temperature and precipitationTundra Starting at the most northerly areas of vegetation we find an openlandscape of mosses lichens and dwarf willows dotted with smallponds and laced with clear streamsGeographyArtic tundra rings the top of the globe covering most of thelands north of the Artic CircleClimateTypically cold and dryShort summersPrecipitation varies from less than 200mm to a little over600mmPrecipitation exceeds evaporation summers are soggy and thetundra landscape is filled with ponds and streamsSoilsSoil building is slowRates of decomposition are low organic matter accumulates indeposits of peat and humusPermafrost permanently frozen layer of soil that remainsmonthsfrozen even during the summer Solifluciton slowly moves soils down slopesFreezing and thawing brings stones to the surface of the soilforming netlike or polygonal pattern on the surface of tundrasoilsBiologyDominated by perennial herbaceous plants grasses sedgesmosses and lichens warf willows and birches lowgrowingshrubsShort periods of warm weather suitable for plant growthpresent significant challenges to the residents of the tundraslow growing with nearly all of the biomass below groundshort with strong stems continuous photosynthesisCaribou reindeer musk ox bear wolves artic fox weasellemming ground squirrel ptarmigan and snowy owlHuman influencesIntense exploration and extraction of oil natural gas and avariety of minerals such as diamondsRapidly rising temperatures on the permafrost and rates ofdecompositionAs permafrost melts the rich organic material it containsbecomes available to soil microbes and insects fordecomposition potentially releasing enormous amounts of CO2 Boreal forest 11 of earths land areaGeographyConfined to the Northern HemisphereClimateWinters are usually longer than 6 months and summers are toshort to support temperate forestPrecipitation ranges from 200600mmBecause of low temperatures and long winters evaporationrates are low and drought is either infrequent or briefSoilsLow in fertility thin and acidicLow decomposition and low pH slow down decomposition ofplant litter and the rate of soil buildingBiologyEvergreen conifersSteep vertical gradient in light as one moves from the top of thecanopy to soil surfaceStrong vertical gradient in ambient temperatures as you movedown through the canopy and down to the soil surfaceBogs and fens dominated by moss species which havewaterlogged soils with islands of vascular plants centeredaround a few trees and shrubs
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