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Primary Succession • Succession is the step by step process where one plant species establishes and is then out competed by another until the area reaches the climax community that can not be out competed. • Primary Succession starts from bare rock that becomes exposed due to glaciers, geologic uplift, and volcanoes. • Soil must be established first before plants can begin to inhabit an area which takes a long time. • In many areas Lichen is the pioneer species that first establishes on bare rocks and aids in erosion. Primary Succession Secondary Succession • Secondary succession takes place in an area that already has an ecosystem established but becomes disturbed by fire, flood, logging, agriculture or any other disturbance. • After the disturbance the system will again start moving toward the climax community. • The size and type of disturbance determines which stage of succession the system will start over from and how long it will take. Secondary Succession Mt. St. Helens • http://www.youtube.com/watch?v=pGImks oOwtU&feature=fvwrel • http://www.youtube.com/watch?v=xP2dre OI8gI • http://www.youtube.com/watch?v=UK-hvgP2uY Productivity • Productivity- the rate of growth or biomass increase in plants and animals. • Gross Primary Productivity (GPP)- is the total gain in energy or biomass per unit area per unit time before any gets used for respiration (R). • Net Primary Productivity (NPP)- is the energy/biomass that remains for the next trophic level. (NPP=GPP-R) Changes During Succession • The size of organisms increases • Simple food chains become more complex • Soil depth, humus, water retention, mineral content and cycling all increase. • Biodiversity increases in early stages but decreases as climax is reached • NPP and GPP increase in early stages and decrease as climax is reached • Production:Respiration ratio gets closer to 1 as climax is reached