Second-growth

A secondary forest (or second-growth forest) is a forest or woodland area which has re-grown after a timber harvest, until a long enough period has passed so that the effects of the disturbance are no longer evident. It is distinguished from an old-growth forest (primary or primeval forest), which has not recently undergone such disruption, and complex early seral forest, as well as third-growth forests that result from harvest in second growth forests. Secondary forest regrowing after timber harvest differs from forest regrowing after natural disturbances such as fire, insect infestation, or windthrow because the dead trees remain to provide nutrients, structure, and water retention after natural disturbances. However, often after natural disturbance the timber is harvested and removed from the system, in which case the system more closely resembles secondary forest rather than complex early seral forest.

Depending on the forest, the development of primary characteristics may take anywhere from a century to several millennia. Hardwood forests of the eastern United States, for example, can develop primary characteristics in one or two generations of trees, or 150–500 years. Often the disruption is the result of human activity, such as logging, but natural phenomena that produce the same effect are often included in the definition. Secondary forests tend to have trees closer spaced than primary forests and contain less undergrowth than primary forests. Secondary forests typically were thought to lack biodiversity compared to primary forests, however this has been challenged in recent years. Usually, secondary forests have only one canopy layer, whereas primary forests have several.

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