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When a species is endangered as a consequence of habitat degradation rather than outright habitat loss, protecting the species may require restoring the habitat to a more natural state. Without human assistance, many degraded ecosystems recover very slowly, if at all. Restoration ecology involves renewing degraded ecosystems by active human intervention. Ideally, restoration involves reestablishing the original structure and function of native ecosystems through such techniques as active removal of pollutants or non-native species, revegetation to reestablish habitat and food resources, reintroduction of native species, and reestablishment of hydrological processes or disturbance regimes. For example, many species depend on particular patterns of disturbance, such as fire or windstorms, to maintain their populations (see Key Concept 56.4).

Recognition of the need for periodic disturbance to maintain healthy ecosystems is a relatively new dimension of conservation biology. We know, for example, that many plant species require periodic fires for successful establishment and survival, but for many years the official policy of the U.S. Forest Service, symbolized by the iconic mascot Smokey Bear, was to suppress all forest fires. Today, however, controlled burning is common, particularly in western North America. In order to use fire as an ecosystem management tool, it is important to know the historical pattern of fires in an area, which can be determined in part by studies of the annual growth rings and fire scars of trees. A schedule of controlled burning that recreates the historical pattern can reduce forest floor litter, avoiding a buildup of fuel that can lead to intense, tree-killing canopy fires.

Sometimes restoration involves using species that act as ecosystem engineers to help restore the original ecosystem. For example, as Key Concepts 56.3 and Figure 56.12 described, the recolonization of beavers, once hunted to near extinction on Minnesota’s Kabetogama Peninsula, resulted in more wetlands and higher species diversity as a consequence of the beavers’ dam-building activities. You’ve seen also how vegetation such as grasses can be planted to facilitate sediment capture, accretion, and ultimately the restoration of sea-grass beds, salt marshes, and sand dunes for habitat and coastal protection.

A large-scale terrestrial grassland restoration project—coined the “American Serengeti”—is under way in northeastern Montana. The goal of the project, which is run by the World Wildlife Fund and American Prairie Reserve in cooperation with public land managers and several other private conservation organizations, is to restore and conserve the native prairie and its fauna over a 1.2-million-hectare area near the Missouri River (Figure 58.15). When Lewis and Clark mapped this region 200 years ago, they saw large herds of bison, elk, deer, and pronghorn as well as abundant populations of their predators. But by the middle of the twentieth century, most North American prairies had been converted to cropland or were heavily grazed by domestic livestock, reducing the herds of large mammals to small remnant populations. Most of these populations are too small to maintain their genetic diversity or to function in their original ecological roles. However, the species have survived, so opportunities exist to reintroduce them if their habitat can be restored.

This ambitious restoration and protection project is feasible for three reasons. First, the private land in the area is owned by a small number of ranchers, each of whom owns extensive grazing leases on public lands administered by either U.S. federal agencies or the State of Montana. Second, most of the land has never been plowed, so native vegetation may recover rapidly when grazing pressures are reduced. Third, the area’s human population is decreasing. Ranchers are aging, and some of their children are leaving for careers in urban settings. Once free-ranging herds of several thousand bison and large numbers of elk—along with their predators (wolves)—have been established, nature-minded tourists are expected to flock to the area to view the wildlife spectacle. Over the long term, the restored ecosystem should deliver major economic benefits to the region.