How Ecosystems Work Ch. 5, Section 3: How Ecosystems Change Standards: SEV1a, b, d, e, SEV5c

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. Top picture- climax community for desert Bottom picture- climax community for forest

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 The bottom picture is of a new show called Revolution. This show depicts what happens after the power goes out around the planet. Notice how secondary succession is taking over the Chicago baseball stadium.

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. Picture on bottom left: Jack pine cone BEFORE fire- seeds are inside sealed cone. Picture on bottom right: Jack pine cone AFTER fire- cone has popped open & released seeds.

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?