Succession, a fundamental ecological concept, refers to the predictable changes that occur in a habitat over time. Throughout the successional process, plant species come and go. When a field is plowed and then abandoned for 100 years, a predictable series of habitat stages occurs. First, herbaceous weedy species appear, such as dog fennel, broomsedge and goldenrod, followed a few years later by shrubs such as wax myrtles and yaupon holly. Within five to six years sapling trees, such as loblolly pines, sweetgums and live oaks, begin to populate the field, eventually shading out low-growing herbaceous plants and shrubs. After 50 years, mature pines begin dying because of lightning strikes or beetle infestations. Then the understory hardwood saplings grow up quickly to fill in the gaps. A century after the field is abandoned, it becomes a mature mixed hardwood-pine forest.