A seral stage is a specific vegetation community occurring on a site at some point in time. When the trees in a forest are cleared during a disturbance (e.g., logging or wildfire), the land does not return to its former forested state in a single step. Rather, one vegetation community is gradually replaced by another. Early seral is the first stage in forest development following any disturbance. An early seral, or early successional community is made up of the first colonizers of a forest opening, or by species that survive the disturbance. The mid-seral stage follows the early seral stage, and is the stage when forests naturally thin.