This species is one of a number which have been included in various “Pleistocene rewilding” plans. Pleistocene rewilding is the proposed practice of restoring ecosystems to their state in the Pleistocene, roughly 10,000 years ago. This contrasts the standard conservation benchmark, particularly in North America, of restoring ecosystems to their pre-Columbian or pre-industrial state. In both Eurasia and North America, the Pleistocene was characterized by much greater diversity and numbers of large herbivores and predators, including proboscidians, equids, camelids, and felidae (Donlan et al 2006; Zimov 2005). The process of restoration would involve the reintroduction of extant species in their historic range, as well as the introduction of ‘proxy organisms’ to replace the ecological functionality of extinct organisms (Donlan et al 2006).
There are three central theoretical goals to Pleistocene rewilding. In Siberia, a team led by Sergey Zimov is investigating the role of large herbivores as ecosystem engineers. It is thought that herbivory pressure could play a central role in maintaining a grass-dominated plant community, as opposed to either tree- or moss-dominated. Grasslands are known to be more stable carbon sinks than either mossy or forested tundra, due to the rapidity of their biogeochemical cycling (Zimov 2005). In principle, then, reintroducing Pleistocene fauna could have positive climate change mitigation effects. Proposals in North America have focused instead on the preservation of ecological dynamics. Proponents of Pleistocene rewilding argue that due to the strong ecological interactions of megafauna, it is likely that their extinction at the end of the Pleistocene would have caused cascading ecological disruptions lasting until the present time (Donlan et al 2006). Additionally, introduction programs could provide a new lease on life for extant, endangered megafauna species, such as cheetahs and Asian elephants (Rubenstein 2006).
Pleistocene rewilding, while headline-grabbing, is by no means the standard of modern conservation biology. There are a number of objections to the proposals of Pleistocene rewilders, summarized by Rubenstein et al (2006). The introduction of species which have been locally extinct for thousands of years, and more particularly the introduction of modern relatives of extinct species, carries many risks: the potential for invasive species, catastrophic disruption of existing ecosystems, inadvertent introduction of disease organisms, and unpredictable behavior of introduced species. Additionally, while paleoecology is a growing field, there is still a fair amount of uncertainty about the actual ecosystem functions of the Pleistocene.
Species which Zimov and his colleagues in Siberia are experimenting with bison, musk oxen, Przewalski’s horse, and Siberian tigers (Zimov 2005). Small-scale introductions have already begun in Yakutia. Donlan et al propose introducing Przewalski’s horse, Bolson tortoises, Bactrian camels, cheetahs, lions, and elephants into the Western United States (Donlan et al 2005). While some individuals of these species are present on privately owned land, there are no free-living populations in North America at this time.