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Terrestrial Ecosystems.docx

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McMaster University
Life Sciences
Luc Bernier

March 7 , 2013 Life Sci 2H03: Environmental Life Sciences Terrestrial Ecosystems Cycling of Elements Sustains the Function of the Biosphere - biosphere plays an important role in nutrient cycling Response of Biosphere to the Physical Climate System - distribution of temperature and precipitation determine, in a particular region:  total amount of organic matter (biomass)  dominant vegetation types  associated organisms - vegetation matches the shifts in the amount of moisture present - less than <25cm are desert - >100cm dense forest - most common vegetation alpine tundra, woodland and grassland Photosynthesis Cycling - ability to fix carbon dioxide using sunlight energy and to create biomass - 6CO +26H O> 2 H O 6 12 - transpiration: plants lose water to the atmosphere - carbon loss: by oxidation and decomposition - nutrients captured from the soil and incorporated in the biomass - disturbance of photosynthesis leads to disturbance in nutrient cycle - energy from sunlight is harvested - used for growth and cell respiration, oxygen by-product - excess matter is stored Succession - communities are in a constant state of disturbance - always adapting to changing conditions - leads to changes in type and distribution of plants - can happen on short time scales or longer time scales - e.g. Primary succession: first stages of colonization of a habitat, tends to be in areas that were covered by glaciers, as they are receding the rocks are devoid of any vegetation, colonization by masses that will break down the rocks and allow nutrient cycling to take place so that more complex plants can evolve, grass, shrubs then trees Secondary Succession - ecosystem has been disturbed - wildfire are the primary causes of secondary succession - grasses take hold and gradually return to a mature forest - time scale involved is fairly lengthy - could be after intense agriculture such as harvesting trees - tends to be faster then primary succession as we are not starting from mosses Major Processes Involved in the Control of Feedbacks in the Climate System - impacts growth and cycling of nutrients - with increase plant growth there’s greater potential for carbon storage reducing the length of the warming by decrease the amount of carbon dioxide in the atmosphere - more precipitation gives more plant growth - warming increases disturbances in the system and decreased ability to store carbon - also feedbacks in permafrost, increase warming, less permafrost and increase in CO 2 - human actions can increase disturbance - physical feedbacks: changes in precipitation affects plant growth and can decrease albedo - complex interactions where the rate of growth impacts the physical makeup of the system Positive Vegetation-Climate Feedback - tundra has higher albedo increasing the high-albedo surface reflect leading to cooling - increased precipitation: forest replaces grasslands resulting in increased transpiration of water vapour and additional local precipitation Photosynthesis and CO Chan2es - temperature influences: the rate of photosynthetic CO uptake 2 - optimal temperature usually varies broadly from one plant to another depending on the types of plants, local habitat and the availability of nutrients - varies with seasons - with increasing temperature the ability of plants to remove or transpire is increased,
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