Restoration Ecology

The simplest applications of restoration ecology focus on the protection of populations of endangered species. In some cases, these efforts can succeed by controlling hunting. For example, on the west coast of North America, populations of the sea otter (Enhydra lutris) were severely overhunted during the fur trade of the nineteenth century, to the degree that the species was thought to be extinct. However, during the 1930s, small populations of sea otters were discovered in the Aleutian Islands and off northern California. These animals were strictly protected, and their surplus production dispersed naturally to colonize other suitable habitat, a process that was aided by some longer-distance introductions by humans. The sea otter is no longer endangered.

Some other previously endangered species of North America whose populations were successfully enhanced mostly by controlling human-caused mortality include the pronghorn antelope (Antilocapra americana), American elk (Cervus canadensis), American beaver (Castor canadensis), Guadalupe fur seal (Arctocephalus townsendi), northern fur seal (Callorhinus ursinus), gray seal (Halichoerus gryptus), northern elephant seal (Mirounga angustirostris), and humpback whale (Megaptera novaeangliae). All of these species had been excessively exploited for their meat or fur, but then rebounded in abundance after hunting was stopped or strictly regulated.

Some other depleted species have been restored by controlling their mortality through hunting, while also protecting or enhancing their critical habitat. The wood duck (Aix sponsa), for example, was endangered by over-hunting for its meat and beautiful feathers, and by degradation of its habitat by the drainage of wetlands and timber harvesting. The species has now recovered substantially because of limits on hunting, the protection of some remaining swamps, and because of programs in which nest boxes are provided for this cavity-nesting species. These nest boxes have also benefited another rare duck, the hooded merganser (Lophodytes cucullatus). An unrelated nest-box program has been crucial in allowing some recovery of abundance of eastern and western bluebirds (Siala sialis and S. mexicana).

Other endangered species have benefited from programs of habitat management, coupled with their captive breeding and release to enhance wild populations or to reintroduce the species to suitable habitat from which it had been extirpated. The endangered whooping crane (Grus americana) has been managed in this way, and this has allowed its abundance to be increased from only 15 individuals in 1941 to 250 birds in 1993 (145 of those individuals were in captivity). Other examples of endangered species that have been enhanced in part by captive breeding and release programs include the eastern population of the peregrine falcon (Falco peregrinus anatum), trumpeter swan (Olor buccinator), wild turkey (Meleagris gallopavo), and pine marten (Martes americana).

Some other endangered species require active management of their habitat, which has become too fragmented and small in area to support the species, or has degraded for other reasons. A North American example of this type of management concerns the endangered Kirtland's warbler (Dendroica kirtlandii), which only breeds in even-aged stands of jack pine (Pinus banksiana) in Michigan. The availability of appropriate habitat for this bird is maintained by planting jack pine, and by the use of prescribed burning to develop the middle-aged stands that are optimal for the warbler. In addition, Kirtland's warbler has suffered badly from the depredations of a nest parasite, the brown-headed cowbird (Molothrus ater). Intense efforts must be made to reduce the population of the parasite within the breeding range of Kirtland's warbler, and to remove its eggs that may be laid in nests of the endangered species. These intensive efforts have allowed the small breeding population of Kirtland's warbler to be maintained. However, the species remains endangered, possibly because of habitat limitations on its wintering range, which appears to be in mountainous areas of Cuba.

In a few cases, restoration ecologists have focused not on particular endangered species, but on entire ecosystems. In such cases, restoration efforts initially involve the protection of remnant areas of endangered natural areas. This must be coupled with active management of the protected areas if this is required to avoid degradation of their ecological integrity. For example, tall-grass prairie is an endangered ecosystem which now exists in much less than 1% of its original extent in North America, almost all of the rest having been converted to agricultural land-use. Ecological reserves are being established to protect many of the last remnants of tall-grass prairie, but these must be managed properly if they are to remain in a healthy condition. The environment of the tall-grass prairie is also capable of supporting shrubs or oak-dominated forest, and will do so unless successional processes are interrupted by occasional light fires, thus requiring seasonal management. The burns are lethal to woody plants, but beneficial to the perennial, herbaceous species of the prairie that thrive in burn cleared areas. Historically, prairie fires would have been ignited naturally by lightning or by aboriginal hunters who were trying to maintain extensive habitat for the large mammals that they hunted. Today, the small remnants of tall-grass prairie that are protected in ecological reserves must be managed using prescribed burns.

The ultimate application of restoration ecology is in the reconstruction of reasonable facsimiles of natural ecosystems, beginning with some degraded condition of land or water. Because of its inherent difficulty, expense, and the need for a commitment over a long period of time, this approach is rare. However, such reconstruction may be necessary to preserve some endangered natural ecosystems, and their dependent species, to a sustainable extent and abundance.

The best example of this intensive, bottom-up practice of restoration ecology is the reestablishment of prairie communities on land that has been used for agriculture for many decades. In such cases, it is assumed that the existing environment is still more-or-less suitable for the occurrence of prairie vegetation, and all that is needed is to reintroduce the component species and to manage their habitat until they can develop a self-maintaining ecosystem. One famous example of this practice is the restoration of prairie on agricultural land in Madison by botanists from the University of Wisconsin, beginning in 1934. The planting and management of these restored prairies has been difficult and time consuming, and great diligence was required to achieve success. Initially, the vigor and persistence of some of the introduced agricultural species, especially several blue-grasses (Poa pratensis and P. compressa), proved to be very troublesome. However, this management problem was overcome by the discovery that these grasses could not survive prescribed burns, while well-established prairie species could.

The successful reconstruction of fairly extensive, semi-natural prairie by dedicated and determined botanists from the University of Wisconsin is a demonstration of the great ecological benefits that can be achieved through restoration ecology. However, this is also an illustration of the great difficulties of restoring indigenous biodiversity.

Wherever feasible, it is much more preferable to preserve species and natural communities in large, self-organizing protected areas, which are capable of accommodating natural ecological dynamics and therefore do not require management by humans to maintain their integrity. Such preservation efforts currently span the globe, from the Asian steppe to the South American rain-forests, but they cover only a minute fraction of threatened and endangered ecosystems.