Primary succession can occur after geological events, such as a volcano eruption that emits lava flow, or glaciers that recede. In both of these cases, a new land emerges that may contain rocks but is devoid of soil and vegetation. Primary succession starts when new organisms, such as lichen and moss, begin to grow on this new formed land.
Lichen is an important organism because its growth leads to the decomposition of rocks that causes soil formation. Lichen and fungi are pioneer species, which are succeeded by other species or communities like moss, grass and plants. The different succession of communities leads to a climax community, also referred to as a biome.
Another type of ecological succession is called secondary succession, which occurs after fires or floods. With secondary succession, there is established soil present. For example, a fire can destroy vegetation and trees in a forest area but the soil remains, and in time, new vegetation grows.