Pioneer species are species which recolonize an area after there has been damage or disruption to the ecosystem. These types of plants are normally hardy plants that need very little to survive, such as lichen or plants with very long roots that give them better access to nutrients.
Pioneer plants also have seeds that can lay dormant for long periods of time, waiting on conditions to improve before growing. Weeds are a common pioneering plant and can grow rapidly to fill the damaged area. These pioneer plants will often die and create plant litter that helps increase the nutrients available for plants that will grow during the secondary succession.