Diagram: Forest Succession
Succession of Plant Communities
Vegetation follows established patterns of re-growth and change after disturbance by farming, timber harvesting, or fire. This process of predictable change in the plant species is called forest succession. Succession on abandoned fields is rapid. Crabgrass and a mixture of other short-lived herbaceous species dominate old fields in the first stage. In the 2nd stage, larger species such as Queen Anne's Lace, asters, and broom sedge raise the height of the vegetation and shade out the crabgrass. Blackberries, sumacs, and other shrubs appear by the third stage. Tree seedlings then begin to rise above the shrub layer, crowding out herbaceous plants in the 4th stage.
On upland fields in central Massachusetts, the earliest invading tree species is white pine. Since the white pine grows faster than the hardwood seedlings, almost pure stands of white pines rise up on abandoned Massachusetts farm land. White pine dominate the canopy for their life span of 80 to 120 years. White pines drastically change the environment beneath them by decreasing the amount of light reaching the ground and using large quantities of water from the soil. This combination makes it impossible for most white pine seedlings to grow in the shade of mature trees. Thus, shade-tolerant hardwood species begin to grow under them and set the stage for the 5th stage in succession. At the end of that stage, the white pine begin to die naturally or become subject to attack by insects or disease. With the pines out of the canopy, the hardwoods grow tall and wide--stage 6. Because most of the hardwood species are able to regenerate in their own shade, the forest continues to mature--stage 7--and maintain itself until the next disturbance.