Primary succession occurs in environments where soil has yet to develop, such as after a volcanic eruption. It starts with pioneer species, like lichens, that create soil. In contrast, secondary succession takes place in areas where an existing ecosystem has been disturbed, such as after a forest fire, and where soil is already present. Both processes lead to the re-establishment of an ecosystem, but primary succession takes longer as it starts from bare rock, while secondary succession is typically faster due to the presence of organic material and seeds.