What defines primary succession in an ecosystem?

Primary succession is characterized by the development of a biological community in an area that was previously devoid of life, such as after a volcanic eruption, glacial retreat, or where soil has been completely removed. This process starts in a barren environment, allowing for the gradual establishment of ecosystems over time. Initially, pioneering organisms such as lichens and mosses colonize the area, leading to soil formation and creating conditions that enable other species to thrive. Over time, this can lead to a mature ecosystem, such as a forest or grassland.

In contrast, rebuilding after a fire refers to secondary succession, which occurs in previously inhabited areas where the soil and some organisms remain, allowing for quicker recovery and regrowth. An area with existing life does not pertain to primary succession, as it implies the presence of biodiversity that has already adapted to the environment. Introducing new species into an old environment does not define primary succession, as it is not about the establishment of life in a barren area but rather about adding species to existing ecosystems. Thus, the defining feature of primary succession is its initiation in an area completely lacking a biotic community.