Trophic rewilding presents regionally specific opportunities for mitigating climate change

Abstract

Large-bodied mammalian herbivores can influence processes that exacerbate or mitigate climate change. Herbivore impacts are, in turn, influenced by predators that place top-down forcing on prey species within a given body size range. Here, we explore how the functional composition of terrestrial large-herbivore and -carnivore guilds varies between three mammal distribution scenarios: Present-Natural, Current-Day and Extant-Native Trophic (ENT) Rewilding. Considering the effects of herbivore species weakly influenced by top-down forcing, we quantify the relative influence keystone large-herbivore guilds have on methane emissions, woody vegetation expansion, fire dynamics, large-seed dispersal, and nitrogen and phosphorus transport potential. We find strong regional differences in the number of herbivores under weak top-down regulation between our three scenarios, with important implications for how they will influence climate change relevant processes. Under the Present-Natural non-ruminant, megaherbivore, browsers were a particularly important guild across much of the world. Megaherbivore extinction and range contraction and the arrival of livestock mean large, ruminant, grazers have become more dominant. ENT Rewilding can restore the Afrotropics and the Indo-Malay realm to the Present-Natural benchmark, but causes top-down forcing of the largest herbivores to become commonplace elsewhere. ENT Rewilding will reduce methane emissions, but does not maximize natural climate solution potential. This article is part of the theme issue ‘Climate change and ecosystems: threats, opportunities and solutions'.

Reintroducing extirpated herbivores could partially reverse the late Quaternary decline of large and grazing species

“…Alternatively, grazers may have been more exposed to hunting or other direct interactions with people by living in open habitats (Johnson, 2002). The global spread of humans was also associated with an increase in grazing livestock (Sandom et al., 2020). So, grazers may have suffered more severely from resource competition (Madhusudan, 2004).…”

“…Yet, the spread of livestock may have been an important driver of ecological change. Many domestic species are grazing ruminants (Sandom et al., 2020), and their introduction may have offset some impacts caused by the global decline of wild, grazing herbivores. We do not believe these reservations invalidate the study’s findings, but we caution the results may apply best to continental, wild herbivore assemblages on macroecological scales.…”

Climate change and ecosystems: threats, opportunities and solutions

“…Sandom et al [22] examine trophic rewilding as a management strategy for restoring ecosystems that may also contribute towards mitigating climate change. Humans have dramatically changed ecological assemblages of largebodied herbivores and predators over the past 50 000 years.…”

Functional traits of the world’s late Quaternary large-bodied avian and mammalian herbivores

“…The causes and ecological legacies of late Quaternary extinctions are key topics of rapidly growing research interest [13][14][15][16][17][18] . Likewise, the potential for introduced herbivores (either inadvertently or intentionally) to restore lost ecological processes is an important focus of research and debate today [19][20][21][22][23][24][25][26][27] .…”