Tolerance model All species that can tolerate conditions on the site are present from the start. Succession is largely the process of tolerant species finding the site, but early arrivers modify the site so that some early arrivers can no longer tolerate the conditions. Succession proceeds until only species that can tolerate the conditions are present. Any species can colonize the early stages. However, early arrivers inhibit the colonization of later arrivals.
Later arrivals can only get in if one of the earlier arrivals dies.
Succession proceeds until all the plants present are long-lived species that resist physical and biological damage. The tolerance model seems to apply to few, if any, situations. In primary succession, the pioneer community begins the process of building soil. Later-succession species can usually not colonize the site until the earlier arrivers have facilitated their entry by building the soil. Nonetheless, even in the early stages, there are some effects of inhibition.