Billings studied the succession of plant species on abandoned fields in North Carolina. Pioneer species consist of a variety of annual plants. This successional stage is then followed by communities of perennials and grasses, shrubs, softwood trees and shrubs, and finally hardwood trees and shrubs. This succession takes about 120 years to go from the pioneer stage to the climax community.
The succession took about 100 years - the succession is more rapid as the starting point was not a bare inorganic surface but actual soil that had already formed.
The case study also shows what happens after a plagioclimax if humans withdraw from an area.