The gradual replacement of one plant community by another. Brought about by changes in climate, in environment, or in the community (climatic succession, physiographic succession, biotic succession), and most frequently by erosion, dropping water levels, or invasion by another species. Succession due to external forces is allogenic, and autogenic when self-prompted. Overall, succession starts with pioneer species and proceeds to those more mature and longer lived (climax). Example: an empty lot taken over by weeds, then bushes, then flowering plants and finally trees.