Presentation on theme: "Ecological Succession -may result from natural orderly changes, or from rapid changes due to disasters, such as fire, etc. -succession occurs as a series."— Presentation transcript:
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 plants and animals colonize a site over time. -the natural process of establishing or reestablishing an ecosystem.
Primary Succession -the first plants to grow are called the “pioneer stage”, and is usually made up 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 taking advantage of limited amounts of nutrients. (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 rock into soil, and create areas where water can gather. -eventually more complex plants start to 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 then give rise to trees. -Plants get larger and more complex as 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 island was formed off the coast of Iceland. It provided scientists the perfect opportunity to study how ecological succession worked in a real-life situation.
1969: Two years after the initial eruptions ceased.
1975: The vegetation has spread, but is still not very diverse. Mostly small mosses, with some grass
1995: More diversity of plants, increased plant 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 never really achieved in nature, because the system achieves maximum biomass and 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 result of destruction or disaster.
Fireweed, Cineraria canadensis growing against a freshly burnt tree stump.
Fireweed growing from a rock cliff
Other examples of Secondary Succession: -farm fields left fallow will eventually return to the condition they were once in.
Pond Succession Step 1: Pioneer stage: small aquatic weeds 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 become a climax community
Step 2: cattails, larger weeds start to grow around the edges of the pond, trapping more soil. Edges of the pond move toward the center. Step 3: Small bushes and plants now grow on land that was once pond. The aquatic plants continue to trap soil, and fill in the pond.
Step 4: Shrubs are replaced with trees, and finally, large trees dominate the community. The area may remain wet and boggy, or may eventually fill in completely, leaving no trace of the former pond.