A pioneer species is a species that is able to colonise an unstable environment, which is very poor in organic matter and features difficult edaphic and climatic conditions: very fine or non-existent soil, lack of water, high heat, etc.
Pioneer species are the first organisms to colonise an environment after it appears (volcanic island) or after a natural disaster (fire, flood, etc.). As pioneer species gradually modify the environment, they will be replaced by other, less specialised or more demanding species.
Pioneer species are therefore characteristic of transitory environments (clearings, sand banks) or extreme conditions (mountain, cliff, etc.).
Bacteria, algae, lichen, moss, some grasses and dicotyledons are some examples of pioneer species.
These lichen and mosses are colonising a new environment: a concrete block. © Jacques Bertrand CC by-nc-nd 3.0
Pioneer species - 1 Photo