What is the main difference between primary and secondary succession?

Primary succession occurs on newly formed or barren land that has never been inhabited before, such as on volcanic islands or glacial moraines. It starts with no existing soil and organisms, so pioneer species such as lichens and mosses begin to colonize the area, breaking down rock and building up organic matter over time. Secondary succession, on the other hand, occurs on land that has been disturbed or altered in some way, such as after a forest fire or logging. In this case, there is already existing soil and seeds present, allowing for a quicker and more diverse return of vegetation and organisms. Primary succession usually takes much longer (hundreds to thousands of years) to reach a stable climax community, while secondary succession can occur in a matter of decades or centuries.