A secondary forest is a forest

Forest

A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...

 or woodland

Woodland

Ecologically, a woodland is a low-density forest forming open habitats with plenty of sunlight and limited shade. Woodlands may support an understory of shrubs and herbaceous plants including grasses. Woodland may form a transition to shrubland under drier conditions or during early stages of...

 area which has re-grown after a major disturbance such as fire

Fire

Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition....

, insect

Insect

Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

 infestation, timber harvest

Logging

Logging is the cutting, skidding, on-site processing, and loading of trees or logs onto trucks.In forestry, the term logging is sometimes used in a narrow sense concerning the logistics of moving wood from the stump to somewhere outside the forest, usually a sawmill or a lumber yard...

 or windthrow

Windthrow

In forestry, windthrow refers to trees uprooted or broken by wind. Breakage of the tree bole instead of uprooting is sometimes called windsnap.- Causes :...

, 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 have not undergone such disruptions, as well as third-growth forests that result from severe disruptions in second growth forests.

Description

Depending on the forest, the development of primary characteristics may take anywhere from a century to several millennia. Hardwood forests

Temperate broadleaf and mixed forests

Mixed forests are a temperate and humid biome. The typical structure of these forests includes four layers. The uppermost layer is the canopy composed of tall mature trees ranging from 33 to 66 m high. Below the canopy is the three-layered, shade-tolerant understory that is roughly 9 to...

 of the eastern United States

Eastern United States

The Eastern United States, the American East, or simply the East is traditionally defined as the states east of the Mississippi River. The first two tiers of states west of the Mississippi have traditionally been considered part of the West, but can be included in the East today; usually in...

, for example, can develop primary characteristics in one or two generations of tree

Tree

A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...

s, or 150-500 years. Often the disruption is the result of human activity, such as logging

Logging

Logging is the cutting, skidding, on-site processing, and loading of trees or logs onto trucks.In forestry, the term logging is sometimes used in a narrow sense concerning the logistics of moving wood from the stump to somewhere outside the forest, usually a sawmill or a lumber yard...

, 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 more undergrowth

Undergrowth

Undergrowth usually refers to the vegetation in a forest, which can obstruct passage through the forest. The height of undergrowth is usually considered to be 0.3 – 3 m . Undergrowth can also refer all vegetation in a forest, which isn't in the canopy....

. Secondary forests typically were thought to lack biodiversity

Biodiversity

Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...

 compared to primary forests, however this has been challenged in recent years. Usually, secondary forests have only one canopy

Canopy (forest)

In biology, the canopy is the aboveground portion of a plant community or crop, formed by plant crowns.For forests, canopy also refers to the upper layer or habitat zone, formed by mature tree crowns and including other biological organisms .Sometimes the term canopy is used to refer to the extent...

 layer, whereas primary forests have several.

Secondary forestation is common in areas where forests have been lost by the slash-and-burn

Slash and burn

Slash-and-burn is an agricultural technique which involves cutting and burning of forests or woodlands to create fields. It is subsistence agriculture that typically uses little technology or other tools. It is typically part of shifting cultivation agriculture, and of transhumance livestock...

 method, a component of some shifting cultivation

Shifting cultivation

Shifting cultivation is an agricultural system in which plots of land are cultivated temporarily, then abandoned. This system often involves clearing of a piece of land followed by several years of wood harvesting or farming, until the soil loses fertility...

 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

Erosion

Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...

 or soil nutrient loss

Soil conservation

Soil conservation is a set of management strategies for prevention of soil being eroded from the Earth’s surface or becoming chemically altered by overuse, acidification, salinization or other chemical soil contamination...

 in certain tropical forests.

Secondary forests re-establish by the process of succession. Openings created in the forest canopy

Canopy (forest)

In biology, the canopy is the aboveground portion of a plant community or crop, formed by plant crowns.For forests, canopy also refers to the upper layer or habitat zone, formed by mature tree crowns and including other biological organisms .Sometimes the term canopy is used to refer to the extent...

 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 effect

Edge effect

The edge effect in ecology is the effect of the juxtaposition or placing side by side of contrasting environments on an ecosystem.This term is commonly used in conjunction with the boundary between natural habitats, especially forests, and disturbed or developed land. Edge effects are especially...

s around mature forest fragments

Habitat fragmentation

Habitat fragmentation as the name implies, describes the emergence of discontinuities in an organism's preferred environment , causing population fragmentation...

 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.

Rainforests

In the case of tropical rainforest

Rainforest

Rainforests are forests characterized by high rainfall, with definitions based on a minimum normal annual rainfall of 1750-2000 mm...

s, where soil nutrient

Nutrient

A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...

 levels are characteristically low, the soil quality may be significantly diminished following the removal of primary forest. In the tropics of South America, growth of new forests from abandoned farmland exceeds loss of primary rainforest. However, due to the diminished quality of soil, among other factors, the presence of a significant majority of primary forest species fail to recover in these second-growth forests.

External links

• M. van Breugel, 2007, Dynamics of secondary forests. PhD Thesis Wageningen University. ISBN 978-90-8504-693-6