Biology 100/101
Lecture 5: Ecosystems in Time (Succession)

"To think about":
Question 5, page 870

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Key Terms:

succession	climax community	pioneer species
disturbance	primary succession	secondary succession
disclimax	environmental change	propagules
soil	soil formation change	prescribed burning

Ecological Succession: Some Definitions

• From the Latin, succedere, to follow after

• Succession is the gradual and directional process of species change in a community resulting from environmental changes brought about by the plants that initially colonize a site barren of life or one that has been disturbed by natural or anthropogenic causes.

• Disturbance of an ecosustem may be caused by many influences:
  • natural disturbances on a variety of scales
  • disturbances caused by human activities

• Succession tends to lead to a climax community that is fairly stable.

Pioneer species: The first species to colonize an area following a disturbance. Pioneer species are present in both primary and secondary succession (see below).

What is Primary Succession? - Soil Formation

• The processes involved in changing an area from one lacking any community (no plants, no animals, no insects, no seeds, etc.) to one consisting of individuals, populations, communities, and ecosystems.

• Primary succession is essentially the same thing as soil formation in terrestrial systems.
  • There is no community because there is no soil.

  • All that is present at the beginning of primary succession is mineral material; sand, volcanic ash, lava, bare rock, etc.

  • Soil contains organic material (living bacteria, fungi, plant roots, animals, etc. and the dead and decomposing parts of these creatures). In primary succession the initial organic matter is added to the mineral substrate by the pioneer plants.

  • Pioneer plants become established on the bare mineral substrate from spores, seeds, or other propagules that are blown, washed, or caried in by animals.

• Examples of Primary Succession
  • See page 856, text

  • Primary succession on bare rock. Rocks erode, sand accumulates, decomposition adds organic matter, and voila! soil. As soil continues to form, larger (and woody) plants appear. lichens and mosses but sometimes higher plants), beginning the process of soil formation.

  • Volcanic eruption is primary succession. Following the eruption, there is no life in the blast zone. Eventually, however, pioneer species of plants do establish themselves, beginning the course of succession.

  • Primary succession can also occur from man-made structures.

What is secondary succession, and how does it differ from primary succession?

• Secondary succession is the reconstruction of an ecosystem following a disturbance that damages or removes all or part of the existing community, BUT leaves the soil intact.

• Secondary succession, as with primary succession, tends to result in the transition of a community from the original pioneer species to climax community.

• Because soil is already present, the rate of secondary succession is much faster than primary succession.

• Pioneer species become established from propagules surviving in the soil or from vegetation in surrounding undisturbed areas.

• Floods, tornadoes, and fires are all examples of naturally occurring disturbances. Notice, however, that none of these completely wipes out the life that was in the area.

1988 Yellowstone Fire: An Example of a Natural and Necessary Disturbance

• What actually happens to the forest community during a fire?

• Yellowstone 1988 fire

• photo of fire along forest floor

• Yellowstone Fire - 6 years later

• Yellowstone fires produce new trees, not meadows

• Secondary Succession in lodgepole pine forest, The Yellowstone Fires, Scientific American, Nov. 1989.

• Not only do plants and animals survive forest fires, but fire provides a diversity of habitats and food sources that many need to survive.

  For Example:

  • the The red cockaded woodpecker, Picoides borealis, is an endangered species from the Southeastern US that lives only in longleaf pine forests that burn every 2 or 3 years.
  • *Lodgepole Pine of the Rocky Mountains, Pinus contorta var. latifolia
  • *White-tailed DeerOdocoileus virginianus
  • * from "Fire Effects Information"

• As a result of studies following the Yellowstone fires of 1988 and subsequent fires, foresters, the public, and politicians as well as ecologists have become aware of the natural role of fire in many ecosystems.

• Prescribed wildland fires

• ENGAGING STAKEHOLDERS TO REINVEST IN PRESCRIBED WILDLAND FIRE, Remarks by Interior Secretary Bruce Babbitt , Tall Timbers Conference, Boise, Idaho, May 9, 1996

• Line of Fire: New Respect for an Old Enemy, Discovery Online

• USDA Forest Service, Caring for the Land

• Fire & Forest Management: Myth & Reality By Evan Frost - Greater Ecosystem Alliance

• NCSA Yellowstone fire information

• Fire Effects Information, an extensive list of species of plants and animals that live with fire.

• In the prairie/oak-hickory forest ecosystem (right here in Urbana-Champaign) there is a tendency towards a forest climax community, but there is continual disturbance that keeps the ecosystem in an earlier stage of succession.

• What do you think is the cause of this disturbance?

• The Tallgrass Prairie in Illinois

• If you are interested - Grand Prairie Friends Homepage

• Agriculture involves creating a disturbance in the prairie ecosystem and then fighting secondary succession. Plowing is a prime example of disturbance, but it can't eliminate:
  • underground plant parts

  • seeds left in the soil from previous years (even 100 years or more)

  • seeds of nearby plants

  • seeds blown in from far away

  A link to John Deere and his plow

  "Weeds" are pioneer species; if farming is discontinued, these colonizing plants will reclaim a field and secondary succession is off and running.

  • See page 857, text

• Pioneer species colonize a bare (primary succession - soil building) or disturbed (secondary succession) site.

• Newly arriving species alter the physical conditions, often in ways that enable other species to become established. (Changes in light, moisture)

• New species of plants displace existing plants because their seedlings are better able to become established and compete with earlier species in the changed environment.

• Animals come in with or after the plants they need to survive.

• Eventually a climax community that is more or less stable will become established and have the ability to reproduce itself.

• Disturbances will start the process of succession again and create a mosaic of ecosystems representing different stages of succession.

Ecosystems in Space and Time in a Changing Climate

• The long term trend is one of a slowly (or possibly rapidly - as recently reported in the NYT) increasing mean earth temperature associated with a rapidly increasing level of atmospheric carbon dioxide.

• What effects will global warming have on biome distribution and the plants and animals existing within?

• Satellite images are used to see what changes have occurred. Here's an example showing the deterioration of an arctic ecosystem due to air pollution.

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