Meredith Cornett

From the scale of the smallest microbe to the top of the food chain, every organism is part of an ecosystem with interdependent relationships. Successful species reintroduction will depend not only on how an organism adapts to its new environment, but also on how fully the ecosystem incorporates the organism into its day-to-day functioning. When planning species reintroductions, restorationists must bear in mind the links among organisms in fully-functioning ecosystems.

Depending upon project goals, species may be reintroduced to an area for a variety of reasons. The motivations for species reintroductions in this volume of Restoration & Reclamation Review generally fall into two broad categories: function and conservation. In the instance of a functional reintroduction, the goal would be reinstating a key process to an ecosystem where it historically occurred. For example, Bonnie Witt addresses the importance of earthworms in the processes of soil organic matter decomposition, soil aeration, and mixing soil horizons. In the case of a conservation species reintroduction, the goal would be the establishment of a new population, particularly in the case of threatened or endangered species. Rachel Fields and Kim Mason provide good examples of conservation reintroductions by outlining strategies for reintroducing plant and butterfly species on the brink of extinction. The distinction between functional and conservation species reintroductions is arbitrary, as the two categories often overlap. I only use the distinction here for the purpose of clarity.

The evaluation of necessity and risk is a critical first step in species reintroduction. Evaluation of the necessity of reintroductions should include an assessment of whether natural dispersal of the organism from surrounding sources will provide sufficient propagules, or whether humans must intervene as "dispersal agents." If dispersal from natural sources is limiting, reintroduction may be a reasonable course of action. What may initially appear to be a dispersal problem, however, might actually be a matter of unsuitable habitat. Bonnie Witt describes a case in which termite species diversity on an Australian mined land restoration site is limited not by dispersal from source populations, but by the availability of leaf litter and decayed logs on the site.

In the case of a threatened or endangered species, dispersal from source populations to a reintroduction site is usually assumed to be limiting and to require human intervention. As with functional species reintroductions, a thorough evaluation of the new habitat's suitability must be conducted prior to reintroduction, and must form the second piece of the project plan. Through a well-documented decision process, managers must choose a level of acceptable risk of failure. The decision process should incorporate information about the species' habitat requirements, genetic variability among the individuals to be reintroduced, and parameters of the reintroduction site. If restorationists decide that the perils the species will experience in its current habitat are greater than those it would experience at the new site, then the reintroduction should proceed. Rachel Fields describes many situations in which rare plants are transplanted from sites slated for the extreme disturbance of development. For such extreme cases, the new habitats are often predicted to improve a plant population's chances for survival.

The best of intentions can go awry. Kim Mason mentions that too often butterfly species go extinct in the very reserves designed to conserve them. In her presentation of case studies of reintroductions of several butterfly species, Mason describes the intricacies of habitat requirements of butterfly species at different developmental stages. Physical and environmental qualities of the reintroduction site, such as the topography (slope, aspect, and elevation) and vegetation must be matched with the requirements of the reintroduced species and perhaps its developmental stage. Parameters that must be included in a habitat suitability assessment are not necessarily obvious. Should the reintroduction fail, a re-examination of parameters initially considered important may reveal other variables that should be considered in future attempts.

The ideal is to avoid species reintroductions and only attempt them when other options do not exist. If an assessment of the initial conditions indicates that a species reintroduction is necessary either for functional or conservation purposes, a number of strategies can be employed. Reintroduction strategies include everything from entirely active approaches to only restoring components of the habitat that will facilitate successful colonization and/or establishment. Natural recolonization is the process by which organisms return to a site on their own, assuming that dispersal of propagules is adequate and that the habitat is suitable. Although not addressed in the following section on species reintroductions, natural recolonization should be recognized as one end of the reintroduction spectrum.

Active reintroduction methods must be carefully chosen to ensure success. Rachel Fields compares the various methods available for endangered plant reintroduction and identifies the best methods as those that minimize damage to the source population and reintroduced individuals, as well as those that maximize genetic diversity. The success of extracting a plant from one site and reintroducing it to another may be improved if part of its native soil is included in the transplanting process. The heightened success rate may be indicative of an intact soil community, an ecosystem in its own right, of which the plant is an interdependent part. Witt likewise describes the use of active approaches, such as transplanting sod plugs as earthworm inocula, as well as restoration of ecosystem components necessary for earthworm recolonization, such as burying leaf litter on reintroduction sites.

Each of the papers in this section exemplifies avoiding the need for reintroductions whenever possible. As critical pieces of the complex ecosystem puzzle, species losses reduce ecosystem resilience by altering processes and diversity. The loss of sensitive species, such as many butterflies, can indicate the presence of disturbances and stressors that may negatively impact additional components of the ecosystem. Successful reconstruction of habitats in new locations are not the norm. Without a significant investment of time, thought, and money, the complexities of habitat requirements for a species seldom can be defined and reproduced at a new site. Even with the best of intentions, and a sound project plan, the fact remains that an ecosystem amounts to more than the sum of its parts. The papers in this section describe noble efforts to prevent further loss of vital ecosystem functions and diversity, but humans cannot pretend to anticipate all the essential ingredients for successful species reintroduction.

Return to the Restoration & Reclamation Review Home Page