Primary Succession

• An area's transformation from barren to ecosystem happens in successive steps. Primary succession happens in an area that hasn't supported life before. In such an area, not even soil exists, so an ecosystem starts from scratch. For instance, when new land is created by lava flow, primary succession transforms it from lifeless basalt to an eventual ecosystem that supports life. The lush Hawaiian Islands are an example of primary succession succeeding.
  
  

Stages of Succession

• Pioneers occupy barren terrain and build soil. These pioneers include lichens, mosses and liverworts. The soil supports grasses and weeds, which let insects, rodents and birds gain a foothold. Shrubs, annuals and perennials come next; these supporting larger herbivores and small carnivores. Trees follow, first the fast-growing kinds, like willow and birch, which become well-established in about 20 years, then slow-growers like oak. Slow-growers become dominant in the forest in about three-quarters of a century, supporting the biggest animals: coyotes, elk and bear, for instance.
  
  

Climax Communities

• When succession continues until relative stability is achieved, it results in a climax community. When a climax forest boasts trees that are mostly 200 years old or so, the community is called an old-growth forest. Though the plants and animals from earlier stages are still present, the shaded conditions provided by the trees do not allow for them in the same numbers. Not all ecosystems reach this state. In places where the climate or other conditions don't allow succession to continue, for instance, deserts or tundra, succession stops when shrubs, annuals and perennials are established.
  
  

Lake Succession

• In a lake, ecosystems start with sunshine, which causes algae to grow. The algae becomes food for microscopic organisms. Meanwhile, the oxygen that algae makes as part of photosynthesis allows fish and other animals to live in the lake. Small fish can now populate the lake from streams, eating the microorganisms and using the oxygen. The small fish produce carbon dioxide, which allows plant life to grow in the lake. The algae, fish, microorganisms and plants all have a role to play in the lake's life. Each is said to occupy a niche.
  
  

Secondary Succession

• When a natural disaster occurs in an area, say, a fire, flood or windstorm, secondary succession begins. Though plant and animal life may have been nearly destroyed, ready soil remains. Within that soil lies seeds. Roots, too, exist in the soil, and plants regenerate from those, for instance, fast-growing aspen and birch. Plant seeds also come in from elsewhere and begin to establish themselves. Some plants have even evolved to reestablish themselves after a fire. The lodgepole pine produces cones that release seeds only in answer to the intense heat of a forest fire. Over time, a new ecosystem is established.