HOW ECOSYSTEMS WORKCh. 5, Section 3: How Ecosystems ChangeStandards: 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.

WHAT ARE THE TWO TYPES OF SUCCESSION?

1. PRIMARY occurs on a surface

where no ecosystem existed before

Ex: rocks, sand dune, new island

2. 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?