Ecological successions. The evolution of ecosystems
Primary ecological succession
It is the one that occurs when the ecosystem starts naturally in a newly created environment that has not been colonized by living beings. For example, when volcanic soils, newly formed natural lakes, dunes, new volcanic island, etc. are colonized.
By Joshfn (Own work) [CC BY-SA 3.0], via Wikimedia Commons
Secondary ecological succession
It occurs in an area that was already inhabited by communities but which, due to natural or human causes, have been modified. For example, an abandoned farm field, a forest after a fire, etc.
By Katelyn Murphy (Own work) [CC BY-SA 3.0], via Wikimedia Commons