Primary succession begins in areas with no remnants of an older community, such as after volcanic eruptions or glacial retreat, leaving only bare rock. Over 100+ years in Glacier Bay, Alaska, lichen and mosses colonized the bare rock, which evolved into a hemlock and spruce forest. Secondary succession occurs more quickly on areas where the existing community was partially destroyed by disturbances like wildfires, hurricanes, logging or farming, as the soil remains intact. Every organism alters its environment over time, enabling other species to compete for resources and continue changing the environment further as succession progresses.

1. Lesson Overview 4.3 Succession