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Chapter 2

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Biology 2F03: Fundamental and Applied Ecology Chapter 2: Life on Land 2.1 Large-Scale Patterns of Climatic Variation - Uneven heating of the earth’s spherical surface by the sun and the tilt of the earth on its axis combine to produce predictable latitudinal variation in climate - Temperature, precipitation and atmospheric circulation:  Because the earth is a sphere, the sun’s rays are most concentrated where the sun is directly overhead which changes with seasons o  Earth’s axis is tilted approximately 23.5 away from the perpendicular  June 21 during summer solstice, the sun is directly overhead at the tropic of Cancer, 23.5 N latitude  December 21 during winter solstice, sun is directly overhead at o tropic of Capricorn, 23.5 S latitude  Sun is directly over the equator during the spring and autumnal equinoxes. On March 21 and September 23 rd  Heating of the earth’s surface and atmosphere drives circulation of the atmosphere and influences patterns of precipitation  Air moving from 30 latitude back to the equator completes a thermal loop, which forms the Hadley cell  Polar cell driven by ait movement associated with warming at 60 o latitude and cooling at the poles  Ferrel cells occurs at mid-latitudes, and is driven in part by the effects of the Hadley and Polar cells  Prevailing winds do not move in a straight north-south direction because of the Coriolis effect - Climate diagrams:  Tool to explore the relationship between the distribution of terrestrial vegetation and climate  Summarize climatic information, including: seasonal variation in temperature and precipitation, length and intensity of wet and dry seasons, and the portion of the year during which average minimum temperature is above and below 0 C o  When the temperature line lies above the precipitation line, potential evaporation rate exceeds precipitation (dry periods)  Also include mean annual temperature, precipitation and the elevation of each site above sea level 2.2 Soil: Foundations of Terrestrial Biomes - Soil structure from the long-term interaction of climate, organisms, topography, and parent mineral material - O horizons: found in soils in which the plant material is primarily aquatic in nature - LFH horizons: found in more upland sites - Small organic horizons are found in areas with little litter decomposition or high decomposition rates - Deep organic horizons are found in areas with substantial little inputs and/or low decomposition rates - A horizon: contains a mixture of mineral materials (clay, silt and sand), as well as organic material derived from the organic horizon above - B horizon: contains the materials leached from above, often resulting in a distinctive banding pattern - C horizon: consisting of weathered parent material, broken down through the actions of frost, water, microbial activity, and deep penetrating roots - Under the C horizon we fin unweathered parent material, which is often bedrock - Plants secrete numerous root exudates, which along with the living roots and plant litter, serve as substrates for bacterial, fungal, and animal species - Growth 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 soil - Climate affects the rate of weathering parent materials, leaching of organic and inorganic substances, erosion, and decomposition of organic matter through direct weathering effects 2.3 Natural History and Geography of Biomes - The geographic distribution of terrestrial biomes correspond closely to variation in climate, especially prevailing temperature and precipitation - Tundra:  Starting at the most northerly areas of vegetation, we find an open landscape of mosses, lichens, and dwarf willows, dotted with small ponds and laced with clear streams  Geography:  Artic tundra rings the top of the globe, covering most of the lands north of the Artic Circle  Climate:  Typically cold and dry  Short summers  Precipitation varies from less than 200mm to a little over 600mm  Precipitation exceeds evaporation: summers are soggy and the tundra landscape is filled with ponds and streams  Soils:  Soil building is slow  Rates of decomposition are low, organic matter accumulates in deposits of peat and humus  Permafrost: permanently frozen layer of soil that remains frozen even during the summer months  Solifluciton slowly moves soils down slopes  Freezing and thawing brings stones to the surface of the soil, forming netlike, or polygonal, pattern on the surface of tundra soils  Biology:  Dominated by perennial herbaceous plants: grasses, sedges, mosses, and lichens, warf willows and birches, low-growing shrubs  Short periods of warm weather suitable for plant growth present significant challenges to the residents of the tundra: slow growing with nearly all of the biomass below ground, short with strong stems, continuous photosynthesis  Caribou, reindeer, musk, ox, bear, wolves, artic fox, weasel, lemming, ground squirrel, ptarmigan and snowy owl  Human influences:  Intense exploration and extraction of oil, natural gas, and a variety of minerals such as diamonds  Rapidly rising temperatures on the permafrost and rates of decomposition  As permafrost melts, the rich organic material it contains becomes available to soil microbes and insects for decomposition, potentially releasing enormous amounts of CO 2 - Boreal forest:  11% of earth’s land area  Geography:  Confined to the Northern Hemisphere  Climate:  Winters are usually longer than 6 months, and summers are to short to support temperate forest  Precipitation ranges from 200-600mm  Because of low temperatures and long winters, evaporation rates are low, and drought is either infrequent or brief  Soils:  Low in fertility, thin, and acidic  Low decomposition and low pH slow down decomposition of plant litter and the rate of soil building  Biology:  Evergreen conifers  Steep vertical gradient in light as one moves from the top of the canopy to soil surface  Strong vertical gradient in ambient temperatures as you move down through the canopy and down to the soil surface  Bogs and fens dominated by moss species which have waterlogged soils with islands of vascular plants centered around a few trees and shrubs  Migratory caribou and reindeer, moose, woodland bison, wolves, black bears, grizzly bears brown bears, lynx, wolverines, snowshoe hare, porcupines and red squirrels  Human influences:  Hunting and trapping impact populations of many wildlife species  Cut for lumber and pulp and oil and gas exploration - Temperate forest:  Geography: o o  Found between 30 and 55 latitude  Climate:  Temperatures are not extreme and annual precipitation averages
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