• Secondary succession can generate a forest.forest image by horacio villamonte from Fotolia.com
  
  Secondary succession occurs in an ecosystem when the existing system undergoes a disturbance. In comparison, primary succession occurs when an ecosystem develops on virgin ground from scratch where no ecosystem existed before, at least in recent geologic time. An example of primary succession is the colonization that happened in the aftermath of a continental glacier melting over the northern portion of North America; an example of secondary succession is recolonization of a much smaller area after a fire or hurricane.
  
  

Steady State

• A steady state is a phase in which the ecosystem doesn't change in any dramatic way, at least not as dramatic as in the disturbance event that triggers secondary succession in the first place. The steady state, when depicted on a graph or chart, looks something like the heartbeat pattern of an EKG: the system doesn't stay flat-lined, but fluctuates in a relatively steady pattern as long as there are no major disturbances. The Hubbard Brook researchers are quick to point out in their ecosystem study, though, that the steady state---and a transition phase that precedes it---has merit but may be hypothetical and not actual. This is because natural systems are so complex and are often unpredictable.
  
  

Reorganization

• In this phase, various functional parts of the ecosystem are essentially traumatized, and they react in various ways. One of the effects is that nutrients that had been systematically stored and utilized by the intact system are suddenly more or less released. This has wide-ranging effects, and affects everything from plants and higher animals in the ecosystem down through the invertebrates and microbes.
  
  

Rebuilding

• The intact ecosystem is an intricate assemblage of disparate parts that function together in an organized way. After the reorganization phase comes a rebuilding or restructuring of some or many of the system's functional relationships. New plants grow, and some---whether woody plants like trees and shrubs or non-woody herbaceous plants---are classed as pioneers. This means that they are adapted to growing in an open, more disturbed area. They function in secondary succession to reoccupy the site--they pave the way for the later organisms that are better adapted to a more mature ecosystem.
  
  One interesting effect of secondary succession is a strategy that some plants have adapted to advance their next generation. It's called the buried-seed strategy, and the pin cherry tree is a prime example of this. The pin cherry produces seeds that can lie dormant for decades in the soil under a maturing forest of other tree types. In the event of a disturbance, like a clear-cutting or a hurricane, the seeds germinate and the small pin cherry trees occupy the site. In so doing, they stabilize the site and help prevent erosion, among other effects. The pin cherry is a temporary occupant, and eventually trees and shrubs of other species take over.