Secondary forest

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The forest in Stanley Park, Vancouver, Canada is generally considered to have second and third growth characteristics. This photo shows regeneration, a tree growing out of the stump of another tree that was felled in 1963 by Typhoon Freda.

Secondary forest is a woodland area which has re-grown after a major disturbance such as fire, insect infestation, timber harvest or wind throw, and a long enough period has passed so that the effects of the disturbance are no longer evident. It is distinguished from an old growth or primeval forests, which have not undergone such disruptions, as well as third growth forests that result from severe disruptions in second growth forests. Depending on the forest, the regeneration may take anywhere from a century to several millennia. Hardwood forests of the eastern United States, for example, can develop old-growth 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 many people include natural phenomenon that produces the same effect in the definition. Secondary forests tend to have trees closer spaced than primary forests and contain more undergrowth. Secondary Forests typically have less biodiversity than old growth forests. Usually, secondary forests have only one canopy layer, whereas old growth forests have several.

Secondary forestation is common in areas where forests have been lost by the slash-and-burn method, a component of some shifting cultivation systems of agriculture. Secondary forests may also arise from forest that has been harvested heavily or over a long period of time, forest that is naturally regenerating from fire and from abandoned pastures or areas of agriculture. It takes a secondary forest typically forty to 100 years to begin to resemble the original old-growth forest; however, in some cases a secondary forest will not succeed, due to erosion or soil nutrient loss in certain tropical forests.

Secondary forests re-establish by the process of sucession. Openings created in the forest canopy allow sunlight to reach the forest floor. An area that has been cleared will first be colonized by pioneer species. Even though some species loss may occur with primary forest removal, a secondary forest can protect the watershed from further erosion and provides habitat. Secondary forests may also buffer edge effects around mature forest fragments and increase connectivity between them. They may also be a source of wood and other forest products.

Today most of the forest of the United States, the eastern part of North America and Europe consist of secondary forest.