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

2. 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

3. 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

4. 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

5. 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.

6. 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.

7. 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.

9. old field secondary succession
Farmers field becomes a forest.
Pioneer species of grasses establish quickly due to rich soil.

10. 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.

11. 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?