Reintroduction refers to the deliberate release of animal and plant species into the wild. Many biologists prefer the term reestablishment, to enforce the idea that reintroduction involves native species, rather than new plants and animals. Typically, reintroduction is done with species which have become extinct or endangered in the wild, in an attempt to build wild stocks back up so that the species can enjoy its native habitat.
When an animal population in the wild declines alarmingly, many conservationists attempt to capture representatives of the species, in the hopes of creating a thriving captive colony. Frequently, zoological parks and conservation organizations will trade animals with each other, ensuring healthy stocks of animals without inbreeding. When the captive population gets large enough, members will be let back into the wild, ultimately creating a colony of wild animals where one might have been lost forever.
In order for reintroduction to work, scientists and biologists must work closely together. First, they must determine why the species began to decline in the first place, so that the conditions which brought about the reduced population can be addressed. In Africa, for example, poaching is a serious problem for many native species. If biologists want to reintroduce animals, they need to first eliminate poaching, so that the reintroduced population won't be hunted.
In the case of animal species, while the animals are captive they must be treated like wild animals so that they can survive in the wild. This is a big risk with young animals, who may imprint on humans and become accustomed to captive life. Once the animals are released into the wild, they are closely monitored to ensure that they stay healthy and establish a breeding colony. It may take many years for the animal population to build to a robust level.
In the case of plants, reintroduction can restore biological diversity in a region which has been heavily exploited. Reintroduction may be used to restore native foliage to a barren site, or to choke out nonnative plants which have infested an area. Plants may also be reintroduced in tandem with animals, to provide a reliable and familiar food source for the animal species so that they will be comfortable in their native home.
In either instance, a captive population is retained to refresh wild stocks. The captive population can also be used to breed new animals and plants, in the event that the reintroduction effort does not work. Around the world, many organizations sponsor reintroduction programs, and several successful efforts have occurred in places as diverse as Oman, Ireland, and Mongolia.