Succession and Forest Habitats Background
It is estimated that, at one time, 90 percent of the Chesapeake Bay watershed was covered with forests. Today less than 60 percent is forested. Not only has the watershed lost a third of its forests since 1607, but also many that remain are fragmented. Fragmentation occurs when a forest of many acres is divided into smaller sections by the building of roads, housing developments, and shopping centers. Forest loss and fragmentation negatively impact forest wildlife, the water resources throughout the watershed, and the Chesapeake Bay itself.
The loss of forests means the loss of invaluable environmental benefits. Forests are highly effective in providing food and shelter for wildlife, shading and cooling stream water for fish, reducing erosion and flooding, filtering pollution out of rain runoff, and cleaning the air by removing carbon dioxide and releasing oxygen. Large areas of forest provide more specific benefits. Some wildlife need large unbroken areas of forest to survive; others use unbroken forests as travel corridors. When forests are fragmented, wild animals do not have as much cover from predators. They are more likely to encounter humans and our litter, pesticides, and other toxic pollutants. Fragmentation also provides a foothold to invasive non-native species of plants and animals. With more forest edges, there are more opportunities for the non-native species to enter the forest ecosystem. This often upsets the balance within the ecosystem, as invasive species compete with native ones for food, water, and space.
The natural growth of a forest, from a field to a mature forest, is called succession. Just as individual animals and plants go through distinct lifecycle stages, so do forest ecosystems. Many trees have longer life cycles than humans, so we do not often think about how long it takes for a forest to grow back after we cut it down. Softwood trees such as pines take 40–45 years to reach maturity, and hardwood trees such as oaks take 80–100 years. A forest can be cut down in weeks; however, it can take up to 150 years for the forest to return to maturity, going through succession to reach what is called its mature, final, or climax stage.
A forest on land that has been completely cleared through farming, fire, or clearcutting goes through six stages in succession:
Stage 1 – field of annual grasses and wildflowers*
Stage 2 – meadow of annual and perennial plants*
Stage 3 – brush which includes shrubs and softwood (pine) seedlings*
Stage 4 – pioneer forest composed of softwood (pine) trees
Stage 5 – middle stage forest with some immature hardwood trees
Stage 6 – final, mature, or climax forest with many large, mature trees as well as some dead, decaying ones and some seedlings growing to take their places