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Ch. 5, Section 3: How Ecosystems Change Standards: SEV1a, b, d, e, SEV5c How Ecosystems Work
What is ecological succession? • A gradual process of change and replacement of some or all of the species in a community. • Can take 100’s or 1000’s of years. • Ends in a climax community
What is a climax community? • Final, stable community. • Generally remains the same if undisturbed • Type of climax community will vary depending on ecosystem • Climax community for a desert is different from tropical rainforest • Both primary & secondary succession end with a climax community.
What are the two types of succession? • PRIMARY • occurs on a surface where no ecosystem existed before • Ex: rocks, sand dune, new island • SECONDARY • Occurs on a surface where an ecosystem has previously existed. • Ex: after fire, volcano, flood, abandoned farm
What are the steps of primary succession? Typical primary succession of forest: • Rock is physically & chemically weathered & broken down to make soil. • Physical- frost wedging- frozen water expands & creates cracks • Chemical- pioneer species like lichens & moss can secrete acids to dissolve rock. • Thin soil can support grasses • As grasses die & decompose they contribute to soil layer and soil gets thicker. • As soil thickens it can support larger plant life like shrubs • First trees that grow are usually sun loving trees like pines • As pines grow tall they shade their saplings, saplings can’t get sun and die off. • Shade loving trees like deciduous trees (oak, hickory) grow under pines, eventually outgrowing and replacing pines.
What are the steps of secondary succession? • Soil is already established so it doesn’t have to be created. • Takes less time than primary • More common than primary succession • Pioneer species- grasses, weeds • Shrubs • Pine trees • Deciduous trees • 3 examples: • After a fire • After a field is abandoned • Pond becomes a forest
Fire & secondary succession • Some ecosystems rely on natural fires to maintain the ecosystem. • Ex: grasslands, chaparral • Fires are actually beneficial: • Jack pine trees need intense heat of fire to release seeds • Animals eat new, soft plants that sprout right after fire when soil is nutritious • Minor forest fires burn accumulation of brush & deadwood that would otherwise contribute to major fires.
old field secondary succession • Farmers field becomes a forest. • Pioneer species of grasses establish quickly due to rich soil.
Pond to forest succession • Ponds can fill in and become a forest if not maintained. • Pond fills in with dead leaves, debris, eroded sediment. • Makes pond more shallow. • Sunlight helps plants grow in shallow pond • Eventually fills in completely with sediment & secondary succession continues.
Questions to ask yourself… • What is the difference between primary and secondary succession? • What role does a pioneer species play during the process of succession? • Why would putting out forest fires be damaging in the long run? • What role do lichens play in primary succession? • How are lichens similar to the pioneer species that colonize abandoned farm areas? How are they different?