Ecological Succession

-may result from natural orderly changes, or from rapid changes due to disasters, such as fire, etc.

-succession occurs as a series of plantsand animals colonize a site over time.

-the natural process of establishing orreestablishing an ecosystem.

Primary Succession

-the first plants to grow are called the“pioneer stage”, and is usually madeup of moss and lichens, but can also be grasses,depending on conditions.

-occurs on sites that have not been previously occupied. Ex: new lava flows, sunken ships,newly exposed sandbars.

Pioneer stages may also be termed“early successional”

Early successional organisms are capable of enduring large variations and harsh habitat conditions.

They are also very good at takingadvantage of limited amounts ofnutrients. (or of large amounts)

Mt. St. Helens

Cordgrass, Spartina alteniflora,colonizing a new sand dune.

Lichens attached to a rock

Lichens and moss break down the rockinto soil, and create areas where watercan gather.

-eventually more complex plants startto grow, like ferns and grasses.

-As these pioneers die and decompose, they enrich the soil, which allows larger plants to grow.

Small plants eventually give rise to larger plants, like shrubs, which thengive rise to trees.

-Plants get larger and more complexas succession proceeds to climax

ex: grasses lead to trees

-as each plant dies, they make the soil richer and more fertile.

Surtsey Island: A study in succession

In the early 1960’s a new volcanic islandwas formed off the coast of Iceland.

It provided scientists the perfect opportunityto study how ecological succession workedin a real-life situation.

1969: Two years after the initial eruptions ceased.

1975: The vegetation has spread, but isstill not very diverse. Mostly small mosses, with some grass

1995: More diversity of plants, increasedplant cover.

Climax State-A community in the climax state is one that is in its most mature state of development.

-not all climax communities are forests.Ex: grasslands, tundra.

Ex: Maple-Beech forest, mature coral reef

A true climax community is neverreally achieved in nature, because the system achieves maximum biomassand diversity during mid-succession.

As the system ages, diversity and biomass may decline, especially depending on the abiotic conditions.

Old growth forest,British Columbia

Coral cave, Baja California

Mature coral reef, St. Lucia

Secondary Succession

-it does not begin with bare rock, but with small plants and grasses. If left alone, it will return to the climax community it once was.

Ex: forest fire

-secondary succession occurs as a resultof destruction or disaster.

Fireweed, Cineraria canadensisgrowing againsta freshly burnttree stump.

Fireweedgrowing froma rock cliff

Other examples of SecondarySuccession:

-farm fields left fallow will eventuallyreturn to the condition they were oncein.

Pond Succession

Step 1: Pioneer stage: small aquaticweeds surround the pond, trap soil as it is washed into the pond

-a pond is not a climax community,eventually it will fill in and becomea climax community

Step 2: cattails, larger weeds start togrow around the edges of the pond,trapping more soil. Edges of the pond move toward the center.

Step 3: Small bushes and plants nowgrow on land that was once pond. Theaquatic plants continue to trap soil, and fill in the pond.

Step 4: Shrubs are replaced with trees,and finally, large trees dominate thecommunity.

The area may remain wet and boggy, or may eventually fill in completely,leaving no trace of the former pond.

PondSuccession