Topic%204%20Forest%20Disturbance%20notes

Topic%204%20Forest%20Disturbance%20notes - Trees and Forest...

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Trees and Forest Forest Disturbance and Nutrient Cycling In California oak woodlands and savannah, individual oak trees create “islands of soil fertility” beneath their canopy. Organic carbon and nitrogen pools are about 50% higher than adjacent grasslands that are not influenced by the oak tree. Mechanisms responsible for enhance soil fertility and soil quality beneath the canopy include: Atmosphere: Accumulation of wet & dry deposition o Wet deposition o Dry deposition – gases & dust Biosphere: Deep roots prevent deep leaching of nutrients Steal nutrients from beyond canopy by extending their roots beyond the canopy Lichens on canopy and bark fix N Mycorrhizae enhance nutrient availability & chemical weathering Return organic matter & nutrients to soil – litterfall, throughfall and root inputs Geosphere: Enhanced chemical weathering o Carbonic acid (CO 2 ) o Organic acids o Chelates Increased cation exchange from soil organic matter Hydrosphere: Increased E.T. = Less leaching o 23% canopy interception o 7% increase in transpiration Lower bulk density Increased macropores Increased infiltration Less runoff Less erosion Removal of individual oak trees leads to a relatively quick loss of the islands of soil fertility. Most of the organic matter and nutrient losses occur in the upper soil horizons, those horizons most strongly affected by nutrient cycling processes of the oak trees. The loss of litterfall input to the soil surface probably has the greatest effect.
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Clearcutting Effects on Nutrient Cycling Clearcut harvesting often results in losses of excess nutrient to stream water as a critical component of the nutrient cycle, plant uptake, is greatly reduced in the first few years following clearcutting. In areas not affected by fog water inputs, the stream yield is increased following clearcutting due to a decrease in transpiration. Increased nutrients plus increased water results in increased nutrient losses by leaching. Important mechanisms:
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Topic%204%20Forest%20Disturbance%20notes - Trees and Forest...

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