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Unformatted text preview: s do (but phase changes may be important) C, N, & P cycles
• All tied to hydrologic cycle • Carbon cycle subsumes trophic webs
• N and P are the two elements most likely to limit plant productivity
• Key for pinkish figures from Begon et al.:
– Solid black lines = strong natural fluxes
– Solid red lines = strong human fluxes
– Dashed black lines = weaker natural fluxes 1 27/03/2013 C cycle
CO2 is the gaseous phase, much C in organisms (food chains), inactive
sedimentary pool of carbonates
Limiting steps involve balance between creation (by
photosynthesis) and respiration/combustion of organic matter Human intervention:
Combustion of fossil fuels, land conversion Stone Age demo: Danish palaeocologists cutting beech trees with stone axes Agricultural impacts on carbon: “Man makes grass”
• Humans deforest land
– As an aid to hunting (burning to open and maintain grasslands)
To provide land for agriculture (cutting and burning)
To remove agricultural “waste” (e.g., rice straw) In N. America, easternmost prairies would revert to forest without fire • An important phenomenon since the dawn of agriculture…
• …recently expanded to global scale.
• Carbon sequestered in trees is released by fire Burning of cut trees 9 10 Growing of pri...
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- Spring '13