Restoration Ecology
Restoration Ecology
Difficulties of ecological restoration
Restoration, rehabilitation, and replacement
Some successful examples of restoration ecology
Restoration ecology refers to activities undertaken to increase populations of an endangered species or to manage or reconstruct a threatened ecosystem. Ecological restoration is an extremely difficult and expensive endeavor, and only attempted when the population of an endangered species is considered too small to be self-maintaining or the area of a threatened ecosystem is not large enough to allow its persistence over the longer term.
Restoration ecology can have various goals. A common focus is on endangered species and their habitat. In such a case, a species might be preserved in its remaining natural habitat, conserved by strictly controlling its exploitation, enhanced by a captive breeding and release program, and/or have its habitat managed to ensure its continued suitability. For example, the Galapagos Islands are maintained undisturbed by human development and multiple endangered species are thus, protected. In a more developed or suburban setting, this method is impractical and too expensive to implement. In the case of the California condor (Gymnogyps californianus ), only few remaining natural habitats are carefully maintained, but the birds themselves are also monitored by visual observation and radio tracking. Several attempts have been made to increase the species population through breeding programs.
If a complement of species is being managed in some region, for example in a national park, the goal might focus on ensuring that all of the known native species are present and capable of sustaining their populations. If some species have been extirpated, there may be an effort to introduce new breeding populations. Habitat management might also be a component of this sort of multi-species goal.
If an endangered natural community is the focus, a project in restoration ecology might attempt to repair degraded remnants that still remain, or try to reconstruct a facsimile of the natural community. Restoration of the natural community may be accomplished by introducing native species missing from the ecosystem, and by managing the local environment to ensure the survival of all components of the community in an appropriate balance. The goal of community-level projects is to restore self-maintaining ecological communities that are as similar as possible to the original. This aspiration is rarely attainable to perfection, although it can be approximated to a significant degree.
Difficulties of ecological restoration
For a number of scientific reasons, it is difficult to undertake management actions in restoration ecology. One important problem is that there is usually an imperfect understanding of the nature of the original ecological communities of place or region. Ecology is a relatively recent science. Therefore, little information about the extent of natural ecosystems before they became degraded by human activities, and of their composition and relative abundance of species, is available. Often, small fragments of natural ecosystems continue to persist in ecologically degraded landscapes, but it is not known if they are representative of the former larger ecosystem.
For example, tall-grass prairie was once a very extensive natural ecosystem in parts of central North America. This ecosystem is now critically endangered because almost all of its original area has been converted to intensively managed agricultural ecosystems. A few small remnants of tall-grass prairie have managed to survive. However, ecologists do not know the degree to which these are typical of the original tall-grass prairie, and what fraction of the original complement of species is now missing.
Another difficulty of restoration ecology is that some natural ecosystems require a great length of time to develop their mature character. As a result, it can take decades and even centuries for some types of natural ecosystems to be restored. Therefore, it is impossible for individual ecologists, and difficult for society, to commit to the restoration of certain types of endangered ecosystems. For example, some types of old-growth forests do not reach their dynamic equilibrium of species composition, biomass, and functional character until at least 300–500 years have passed since the most recent, stand-replacing disturbance. Clearly, any initiative to reconstruct these kinds of old-growth forests on degraded land must be prepared to design with these conditions in mind, and to follow through over the longer term.
Another dilemma facing restoration ecologists is their incomplete understanding of the ecology of the species they are working with, of the relationships among those species, and of the influence of non-living environmental factors.
A problem that must be dealt with in many situations is the fact that environmental conditions may have changed significantly, perhaps permanently. Under an altered environmental regime, it may not be feasible to restore original ecosystem types. Ecologists must then propose alternative restoration plans that compliment or approximate the their original intent.
These various problems of restoration ecology are important, and the difficulties they engender should not be underestimated. However, enormous benefits can potentially be attained by successful restoration of the populations of endangered species or of threatened ecological communities.
Programs of restoration ecology require an integrated application of ecological knowledge. Most activities in applied ecology focus on the exploitation and management of species and ecosystems for the direct benefit for humans, as occurs in agriculture, forestry, and fisheries management. In restoration ecology, however, the exercise in applied ecology is undertaken to achieve some natural benefit in terms of the preservation or conservation of biodiversity and environmental quality.
Restoration ecology is a severe test of our knowledge of ecological principles and of environmental influences on species and their communities. To successfully convert degraded environments and ecosystems into self-maintaining populations takes an extraordinarily deep understanding of the complex principles of ecology.
Restoration, rehabilitation, and replacement
At the species level, the goal of restoration ecology is to develop sustainable populations of target species. At the community level, the goal is to rehabilitate or reconstruct an entire ecosystem, making it as similar as possible to an original natural ecosystem that has become endangered. These desirable goals may not be achievable in some situations, and less lofty aspirations may have to be identified and pursued by restoration ecologists.
If the environment has been permanently degraded, for example, by the massive erosion of soil or the accumulation of persistent pollutants, the only achievable goal for restoration ecology might be to rehabilitate the site to some acceptable ecological condition. This could occur through the development of a community that is reasonably similar to an original type, even though not all native species can be accommodated and there are other important differences in the structure and function of the new ecosystem.
In even more degraded environments, the only attainable goal might be replacement, or the development of some acceptable new ecosystem on the managed site. The criteria for replacement might only be to achieve a stable, self-maintaining ecosystem on the site, using native species wherever possible. This is done to restore some degree of ecological integrity, natural aesthetics, recreational opportunity, and perhaps economically useful productivity such as forest or agricultural products.
Some successful examples of 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 overhunting for its meat and beautiful feathers, and by degradation of its habitat by the drainage of wet-lands 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 re-introduce 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-orless 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, seminatural 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
KEY TERMS
Conservation— The protection, preservation, and careful management of a natural resource with a view to its future availability for us by humans.
Endangered— A class of conservation status in which a species or ecosystem is at risk of imminent extinction throughout all or a significant portion of its range.
Preservation— The protection of biodiversity resources for their own, intrinsic value. Preservation is not necessarily undertaken to achieve some benefit for humans.
Restoration ecology— The application of ecological principles and knowledge to the restoration of populations of endangered species, or to the management or reconstruction of threatened ecosystems.
globe, from the Asian steppe to the South American rainforests, but they cover only a minute fraction of threatened and endangered ecosystems.
See also Captive breeding and reintroduction; Sustainable development.
Resources
BOOKS
Aronson, James, and Jelte Van Andel Restoration Ecology: The New Frontier. Malden, MA: Blackwell Publishing, 2005.
Egan, Dave, Evelyn A. Howell, eds. The Historical Ecology Handbook: A Restorationist’s Guide to Reference Ecosystems. Washington, DC: Island Press, 2nd ed. August 2005.
Falk, Donald A., Margaret A. Palmer, and Joy A. Zedler, ed. Foundations of Restoration Ecology. Washington, DC: Island Press, June 2006.
Loreau, Michel, Shahid Naeem, and Pablo Inchausti. Biodiversity and Ecosystem Functioning. Oxford: Oxford University Press, 2002.
Bill Freedman