Answer: As opposed to the first, primary succession, secondary succession is a process started by an event (e.g. forest fire, harvesting, hurricane, etc.) that reduces an already established ecosystem (e.g. a forest or a wheat field) to a smaller population of species, and as such secondary succession occurs on preexisting soil whereas primary succession usually occurs in a place lacking soil. Four steps of secondary succession, from disturbed soil to hardwoods Ecological succession that begins where an ecosystem was disturbed by an event such as fire, flood, or farming, leaving behind intact soil. 1st year after forest fire, flood, or farmer abandons a field: Weeds grow, 2nd year: Seeds blown in or carried in by animals become new weedy.
D: Where two continental plates are colliding, creating a convergent boundary. One plate slips under the other because of convection currents in the mantle.
