thumb|300px|right|The forest in [[Stanley Park, Vancouver, British Columbia, 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 1962 by the remnants of Typhoon Freda.]]

A secondary forest (or second-growth forest) is a forest or woodland area which has regenerated through largely natural processes after human-caused disturbances, such as timber harvest or agriculture clearing, or equivalently disruptive natural phenomena. 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. Secondary forests are notably different from primary forests in their composition and biodiversity; however, they may still be helpful in providing habitat for native species, preserving watersheds, and restoring connectivity between ecosystems.

The legal definition of what constitutes a secondary forest vary between countries.

Development

Secondary forestation is common in areas where forests have been degraded or destroyed by agriculture or timber harvesting; this includes abandoned pastures or fields that were once forests. While many definitions of secondary forests limit the cause of degradation to human activities, other definitions include forests that experienced similar degradation under natural phenomena like fires or landslides. It typically takes a secondary forest 40 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. Depending on the forest, the development of primary characteristics that mark a successful secondary forest 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. Today, most of the forests of the United States – especially those in the eastern part of the country – as well as forests of Europe consist of secondary forest.

Characteristics

thumb|250x250px|Oak plantings in a secondary woodland, [[Tilgate Forest. This mixed conifer and broadleaf woodland is located in West Sussex, United Kingdom.]]

Secondary forests tend to have trees closer spaced than primary forests and contain less undergrowth than primary forests. Usually, secondary forests have only one canopy layer, whereas primary forests have several. These secondary disturbances can clear the canopies to encourage lower canopy growth as well as provide habitats for small organisms such as insects, bacteria and fungi which may feed on the decaying plant material. Additionally, forest restoration techniques such as agroforestry and intentionally planting/seeding native species can be combined with natural regeneration to restore biodiversity more effectively. Land-use conversions from secondary forests to rubber plantations in Asia are expected to rise by millions of hectares by 2050; as such, the carbon stored within the biomass and soil of secondary forests is anticipated to be released into the atmosphere. Recommendations from the Intergovernmental Panel on Climate Change (IPCC), Convention on Biological Diversity, and REDD+ have led to efforts to reduce and combat deforestation in places like Panama and Indonesia. 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.

See also

  • Land use, land-use change and forestry
  • Land use
  • Overlogging
  • Old-growth forest
  • Ecological succession

Notes

General references

  • CIFOR Secondary Forest
  • FAO Forestry
  • World Resource Institute
  • M. van Breugel, 2007, Dynamics of secondary forests. PhD Thesis Wageningen University.
  • Uzay. U Sezen, 2007, Parentage analysis of a regenerating palm tree in a tropical second-growth forest. Ecological Society of America, Ecology 88: 3065-3075.
  • Rozendaal et al., 2019, Biodiversity recovery of Neotropical secondary forests Science Advances, 2019-03-06