Final answer:
Pioneer species, such as bacteria and lichens, are the first organisms to colonize an area after an extreme disturbance. They alter the environment to allow the establishment of subsequent species, leading to a succession of plant life that concludes with the formation of a climax community over an extended period.
Step-by-step explanation:
After an extreme disturbance such as a fire, the first organisms to move into the area are known as pioneer species. These species typically include bacteria and lichens that are capable of living on bare rock. Pioneer species are instrumental in altering the environment to facilitate the colonization of subsequent species. Through weathering processes assisted by wind and water, pioneer species contribute to soil formation, creating the conditions necessary for the growth of plants like grasses that can thrive in thin, nutrient-poor soil. As these pioneer species grow and die, they add organic matter to the soil, improving its quality and water-retention capacity, and setting the stage for the arrival of more complex plant life such as shrubs and trees.
Following the colonizing efforts of the pioneer species, a succession of other organisms occurs. Grasses and other weedy annual plants are generally the first to grow back, soon followed by more rapidly spreading grasses and pioneer species. This succession continues with the introduction of intermediate species like shrubs and small trees. Over an extended period, potentially over 150 years, a climax community is formed. This climax community is a stable ecosystem that resembles the pre-disturbed state and persists until the next disturbance. It is shaped by the local climate and geology and represents an equilibrium that, while looking static, is actually dynamic with ongoing changes in species abundance and sometimes identities.