Complex mammal species responses to fire in a native tropical savannah invaded by non-native grader grass (Themeda quadrivalvis)

Abstract

Invasive non-native grasses can greatly alter habitat structure. Land managers use fire to reduce invasive grass infestations, a strategy which is intended, at least in part, to reduce the impact of wildfires on fauna. The response of fauna to fire in invasive grass environments may be complex. To examine the responses of fauna to fire and invasive grass we compared mammal richness and abundance in a group of 24 replicated sites in north Queensland, Australia. Our sites were characterised by native kangaroo grass, native black spear grass, or invasive, non-native grader grass, and we surveyed them at three times in relation to fire. First, when they had remained unburnt for 2 years (pre-burnt), just after burning (post-burnt), and up to 15 months after burning (revegetated, i.e., the grass had naturally regrown). Therein, we monitored vegetation structure and mammal richness, abundance and assemblage composition. The lowest overall mammal abundances occurred in sites revegetated after fire (40–55 % lower abundances in revegetated compared to pre-burnt sites), but rufous bettongs (Aepyprymnus rufescens) and tropical short-tailed mice (Leggadina lakedownensis) increased in abundance following fire. Abundance of eastern chestnut mice (Pseudomys gracilicaudatus) and common planigales (Planigale maculata) decreased after fire, but returned with returning grass cover. We detected a gradual decline in northern brown bandicoots (Isoodon macrourus) over the course of the study, with no recovery. We found no evidence that mammals showed stronger responses in invasive than native grasses after fire. Mammal responses to fire were distinctive, some species were more abundant following fire, some less, and some species returned to their prior abundances. Thus, in tropical savannahs, a naturally fire-prone system, overall mammal abundance, but not richness, decreased after fires, in both native and non-native grass, but the responses of individual species varied greatly. Decisions to burn invasive grasses for biodiversity conservation should include an awareness of the likelihood of enhancing certain species while discouraging others.