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positive—more carbon is stored than released. NEP is also positive in lake and ocean sediments and bog and swamp soils where poor aeration limits the rate of cellular respiration.oFossil fuels, the oil, natural gas, and coal that powers our cars and generates much of our electricity, were created eons ago in ecosystems such as bogs, swamps, and ocean sediments with high NEP. Burning those fuels returns that long-stored carbon to the atmosphere as CO2. Disturbance and community changeoBIG IDEA: Ecological disturbances, such as fires, hurricanes, or the logging offorests, may result in the loss of many or all of the species in an ecological community. Environmental features that are left behind following a disturbance, such as soil and woody debris, are called ecological legacies. As species reestablish themselves, they alter the environment, often making it possible for other species to become established. This process of post-disturbance change in an ecological community is called succession. It often
leads to diverse and stable ecosystems such as the Pacific Northwest old-growth forests. The nature of successional change is influenced by the severity of the disturbance and the ecological legacies that the disturbance left behind. Succession may also influence the likelihood of future disturbances, producing disturbance cycles. The specific patterns of succession vary from place to place and from time to time, depending on factors such as variations in environmental conditions, climate change, and the character of surrounding ecological communities.oPrimary successionOccurs when disturbance removed all ecological legaciesprocess is initiated by pioneer species that facilitate growth of other speciesoccurs slowlyFacilitating species get outcompetedPlant community that can reproduce generation after generation establish a climax community (sometimes) As plant species become established and grow, they may alter the environment around them in ways that make it more habitable for other species. This process, called facilitation, is especially important in the early stages of succession.Facilitating species, such as Dryasand alder, eventually disappear because they are unable to compete effectively with their successors.The migration of plant species to a site depends on the proximity of seed sources and the ability of the plants to disperse their seeds. Early invading herbs and shrubs often have small wind-dispersed seeds and are abundant in nearby locations.The combination of migration, facilitation, and competition results in populations of different species replacing one another over time.Eventually, a community of plants that is able to reproduce generation after generation may become established; this is the climax community. In southern Alaska, the climax community is the group of species associated with a white spruce forest.oSecondary successionEcological change after a disturbance that leaves behind legacies such as soil, seeds or debris