how does an ecosystem transition from primary succession to secondary succession?

An ecosystem does not directly transition from primary succession to secondary succession. Rather, these are two distinct types of ecological succession that occur under different conditions. Primary succession begins on a lifeless area with no soil or organic material, such as bare rock after a volcanic eruption or glacier retreat. Over time, pioneer species like lichens and mosses colonize the area, slowly build soil, and eventually allow more complex plant communities to establish. Secondary succession occurs in areas where an ecosystem previously existed but was disturbed or destroyed, leaving soil and some biological remnants intact—for example, after a wildfire, flood, or human activity like farming. Because soil, nutrients, seeds, and microorganisms are already present, secondary succession proceeds faster than primary succession. In essence, an ecosystem does not "move" from primary to secondary succession. Instead, after primary succession completes and forms a mature community with soil and vegetation, if this community is later disturbed, secondary succession begins as the ecosystem recovers from the disturbance using the remaining soil and organisms. Therefore, the transition from primary succession to conditions where secondary succession could occur requires the initial development of soil and a biological community during primary succession. Once established, if a disturbance impacts this mature community, secondary succession initiates the recovery process. This explains the conceptual connection between the two successions but they are different stages of ecosystem development depending on the presence or absence of pre- existing soil and life.