ENVIRNONMENTAL SCIENCE A

3.3 How Ecosystems Change

Succession

• The types or grangisms in a community follow a regular pattern of change over time, succession.
• Primary succession occurs on bare rock where nothing has ever grown. 
  •  This involves a sequence or stages that is similar to secondary suceesion and ends in a climax community.
• Secondary succession takes place where other commmunities have lived before.
• Eventually a climax community takes hold and persits until it is distrubed.
• Forest fires are a necessary part of secondary succession i n some areas because certain organisms reproduce only after a forest fire has cccurred, such as the jack pine.
• Periodic forest fires may also prevent larger major fires.
• An example of a pioneer species is Lichens, they can grow on bare rock and gradually break the rock down starting the process of soil formation.

Soil Formation

• Soil formation - water can freeze and thaw in cracks in rocks making the rock to breakdown further.  Dust particles in the air are trapped in the cracks and as the dead remains of the lichens and bacteria buld up, mosses later gain hold, breaking the rock some more.  as the mosses die, they decay and are added tothe growing pile or organic material, fertile soil is now beginning to form, seeds are able to germainate and successon begins.