Landscape-Scale Effects of Fire, Cats, and Feral Livestock on Threatened Savanna Mammals: Unburnt Habitat Matters More Than Pyrodiversity

Abstract

Northern Australia has undergone significant declines among threatened small and medium-sized mammals in recent decades. Conceptual models postulate that predation by feral cats is the primary driver, with changed disturbance regimes from fire and feral livestock in recent decades reducing habitat cover and exacerbating declines. However, there is little guidance on what scale habitat and disturbance attributes are most important for threatened mammals, and what elements and scale of fire mosaics actually support mammals. In this study, we test a series of hypotheses regarding the influence of site-scale (50 × 50 m) habitat and disturbance attributes, as well as local-scale (1 km radius), meta-local scale (3 km), landscape-scale (5 km) and meta-landscape scale (10 km) fire mosaic attributes on mammal abundance and richness. We found that habitat cover (rock, perennial grass, and shrub cover) at the site-scale had a positive effect, and disturbance factors (feral cats, fire, feral livestock) had a negative influence on mammal abundance and richness. Models supported site-scale habitat and disturbance factors as more important for mammals than broader-scale (local up to meta-landscape scale) fire mosaic attributes. Finally, we found that increasing the extent of ≥ 4 year unburnt habitat, and having an intermediate percentage (ca. 25%) of recently burnt (1-year burnt) habitat within the mosaic, were the most important functional elements of the fire mosaic at broad scales for mammals. Contrary to expectations, diversity of post-fire ages (‘pyrodiversity’) was negatively associated with mammal abundance and richness. These results highlight the need for management to promote retention of longer unburnt vegetation in sufficient patches across savanna landscapes (particularly of shrub and fruiting trees), maintain low-intensity patchy fire regimes, reduce the extent of intense late dry season wildfires, and to reduce the impact of feral livestock. This study provides further evidence for the role of feral cats in northern Australian mammal declines, and highlights the need for increased research into the efficacy of cat control methodologies in reducing biodiversity impacts in these extensive landscapes.

Tropical savanna small mammals respond to loss of cover following disturbance: A global review of field studies

“…These positive responses could be explained by either increased cover mediated by feral cat predation or increased food resources, as allowed by the investigators (Legge et al, 2011). A large-sample observational study (n = 94) found that total small-mammal abundance and diversity increased, and mortality due to feral cats decreased, as three types of cover-rock, shrub, and perennial grass-increased, and as livestock grazing was reduced (Radford et al, 2021). A 13-year natural experiment with varying levels of livestock grazing and fire extent and intensity concluded that fire and domestic LMH each suppressed small mammals (murids and small dasyurid marsupials) and had a negative synergistic-but not additive-effect on overall small-mammal abundance and richness (but opposite effects on P. delicatulus compared to the four other commonly caught species; Legge et al, 2019).…”

“…Of 17 studies of fire effects conducted in Northern Australia, 12 of which were experimental, six concluded that loss of cover explained significant small-mammal responses (Kutt and Woinarski, 2007;Legge et al, 2008;Kutt and Gordon, 2012;Leahy et al, 2015;Davies et al, 2017;Radford et al, 2021), five concluded that both cover and food resources were partly important as limiting factors (Lawes et al, 2015;McDonald et al, 2016;Ondei et al, 2020;Radford et al, 2020;Penton et al, 2021), and six studies were inconclusive (Pardon et al, 2003;Woinarski et al, 2004;Griffiths and Brook, 2014;Abom et al, 2016;Davies et al, 2018;Legge et al, 2019; Supplementary Table S1, Figure 2). One study found 90% direct mortality of small mammals from intense fires, with the individuals surviving being in unburned refuges (Legge et al, 2008).…”

“…So it is particularly important to understand what landscape factors combine to offer them the best chance of recovery. One prescription is to preserve unburned and ungrazed refuges of vegetative cover for at least 4 years (Radford et al, 2015(Radford et al, , 2021). This will be critical as long as climate change-driven drought and wildfire, and uncontrolled feral cat predation, continue unabated (Woolley et al, 2019;Hale et al, 2021).…”

Long-unburnt habitat is critical for the conservation of threatened vertebrates across Australia

“…However, the loss of long-unburnt habitat patches, with respect to both their frequency and overall representation within landscapes, points to the need for active stakeholder collaboration to design appropriate management plans for landscapes that are managed for multiple, sometimes competing, objectives. Recent studies have begun to quantify age-class distributions of vegetation that would benefit species of conservation concern (Giljohann et al 2018), highlighting the need for a greater extent of long-unburnt vegetation (Davies et al 2018;Radford et al 2021), and there may be opportunities to integrate other values and objectives into these tools.…”

Gaps in Monitoring Leave Northern Australian Mammal Fauna with Uncertain Futures

“…Multiple authors have recommended that a priority conservation action was intensive fire management aimed at increasing the extent of longer-unburnt habitat and in delivering fine-scale patch burning [22,23,145]. A mosaic of fire patches of different ages also has been considered to be the best option for a range of birds, mammals, amphibians, and reptiles found in the savanna landscapes [146], but the mosaic hypothesis is not sufficiently nuanced for management to be effective [136].…”