Forest fragmentation

Deforestation events in New Zealand (district Tasman)

Forest fragmentation is a form of habitat fragmentation, occurring when forests are cut down in a manner that leaves relatively small, isolated patches of forest known as forest fragments or forest remnants. The intervening matrix that separates the remaining woodland patches can be natural open areas, farmland, or developed areas. Following the principles of island biogeography, remnant woodlands act like islands of forest in a sea of pastures, fields, subdivisions, shopping malls, etc. These fragments will then begin to undergo the process of ecosystem decay.

Natural causes

Forests may also be fragmented by natural processes such as fire and changes in climate. For example, 300 million years ago in the Carboniferous the tropical rainforests in Euramerica were fragmented due to a change in climate. There was a great loss of amphibian diversity and simultaneously the drier climate spurred the diversification of reptiles. These changes, however, occurred gradually over million of years, not like the human-driven destruction of tropical rainforests today.

Conservation implications

Forest fragmentation is one of the greatest threats to biodiversity in forests, especially in the tropics. The problem of habitat destruction that caused the fragmentation in the first place is compounded by :

• the inability of individual forest fragments to support viable populations, especially of large vertebrates
• the local extinction of species that do not have at least one fragment capable of supporting a viable population
• edge effects that alter the conditions of the outer areas of the fragment, greatly reducing the amount of true forest interior habitat.

The effect of fragmentation on the flora and fauna of a forest patch depends on a) the size of the patch, and b) its degree of isolation. Isolation depends on the distance to the nearest similar patch, and the contrast with the surrounding areas. For example, if a cleared area is reforested or allowed to regenerate, the increasing structural diversity of the vegetation will lessen the isolation of the forest fragments. However, when formerly forested lands are converted permanently to pastures, agricultural fields, or human-inhabited developed areas, the remaining forest fragments, and the biota within them, are often highly isolated.

Forest patches that are smaller or more isolated will lose species faster than those that are larger or less isolated. A large number of small forest "islands" typically cannot support the same biodiversity that a single contiguous forest would hold, even if their combined area is much greater than the single forest. However, forest islands in rural landscapes greatly increase their biodiversity.

References

Further reading

• Kinver, Mark. (2013, September 26). "Forest fragmentation triggers 'ecological Armageddon'", BBC News.