Forests can grow from bare rocks in about 150 years, according to the U.S. Geological Survey. Many scientists study primary succession in Hawaii because the lava flows from volcanoes create places where primary succession can take place. Because primary succession requires the accumulation of soil, it happens far more slowly than secondary succession does. Secondary succession occurs when a habitat is disturbed, but the soil remains in place.
The process by which primary succession occurs is relatively consistent, regardless of the location in which it happens. Primary succession occurs only in small areas that lack life of virtually any kind. Bare rock forms the substrate on which the process takes place. Initially, lichens colonize the bare rock. Lichens support themselves by leaching acids into the rock and then extracting the nutrients they need. Once several lichens die and other organic matter accumulates on the rock, it begins to retain moisture. This moisture allows mosses to colonize the area. The mosses also collect organic matter that eventually helps to form a thin soil. Grasses and weeds eventually begin growing in the new soil. They help to collect more organic debris, and in the process, produce even more soil. Eventually, enough soil is created to support trees and forests.