Can trophic rewilding reduce the impact of fire in a more flammable world?

Abstract

Large vertebrates affect fire regimes in several ways: by consuming plant matter that would otherwise accumulate as fuel; by controlling and varying the density of vegetation; and by engineering the soil and litter layer. These processes can regulate the frequency, intensity and extent of fire. The evidence for these effects is strongest in environments with intermediate rainfall, warm temperatures and graminoid-dominated ground vegetation. Probably, extinction of Quaternary megafauna triggered increased biomass burning in many such environments. Recent and continuing declines of large vertebrates are likely to be significant contributors to changes in fire regimes and vegetation that are currently being experienced in many parts of the world. To date, rewilding projects that aim to restore large herbivores have paid little attention to the value of large animals in moderating fire regimes. Rewilding potentially offers a powerful tool for managing the risks of wildfire and its impacts on natural and human values.This article is part of the theme issue 'Trophic rewilding: consequences for ecosystems under global change'.

Keywords: ecosystem engineer; fire regime; herbivory; megaherbivore; plant–animal interactions; pyrogeography.

Figure 1.

Locations of studies of effects of vertebrates on fire regimes. These are shown in relation to (a) global variation in mean annual temperature and mean annual rainfall, with biomes superimposed (from [78]), and relative density of fires (hotspot density) as detected at 1 km resolution by the satellite-based Moderate Resolution Imaging Spectroradiometer (MODIS) instrument; and (b) geography, with variation in tree cover also shown. Filled circles are studies demonstrating reduction of fire activity (frequency, intensity or extent) due to herbivores; open circles are studies demonstrating no reduction of fire due to herbivores; and filled squares are studies showing reduction of fire activity by ecosystem engineers. The studies involving herbivory are those listed in table 1 that were conducted at specific localized sites; studies of ecosystem engineers are described in the text. Palaeoecological studies are not included.

Figure 2.

The potential, and complexity, of trophic rewilding for management of fire regimes as illustrated by three case studies detailed in the electronic supplementary material: (a) white rhinos and other large herbivores control fire in conservation reserves in southern Africa (image: Sally Archibald); (b) rewilding of communities of large herbivores may reduce the threat of wildfire in the southwestern USA (image: Louis Harveson); and (c) the introduced swamp buffalo may be an ecological replacement for extinct Pleistocene megafauna in northern Australia with ecological benefits that must be traded off against unwanted impacts (image: David Hancock).