The influences of climate, habitat and fire on the distribution of cockatoo grass (Alloteropsis semialata) (Poaceae) in the Wet Tropics of northern Australia

Abstract

Cockatoo grass [Alloteropsis semialata (R.Br.) A. Hitchc.] is considered a keystone species in northern Australian ecosystems as it provides a food resource for many species, including several endangered vertebrates. This study examined both local and regional environmental factors influencing cockatoo grass distribution and abundance in the Wet Tropics of north Queensland, Australia. Local distribution and abundance were investigated in the sclerophyll ecotone between open woodland and tall open forest, because little is known about cockatoo grass distribution within this habitat; also, the endangered northern bettong (Bettongia tropica) is restricted to this habitat and depends on cockatoo grass for its survival. Regional-scale modelling of distribution was undertaken to examine the climatic tolerances of cockatoo grass in Queensland. Density of cockatoo grass was negatively related to litter cover, soil moisture, and the presence of two dominant grass species, Themeda triandra [Forssk.(R.Br.) Stapf] and Cleistochloa subjuncea (C.E.Hubb.). Soil nutrients (N, C, S, and C : N ratio) were positively related to density of cockatoo grass. A late dry season experimental burn demonstrated that cockatoo grass had high survival to fire, with increased density and flowering in response to fire. Regional-scale modelling using climate variables indicated that cockatoo grass is more suited to the drier end of the sclerophyll habitat range. Cockatoo grass in the woodland-forest ecotone in the Wet Tropics appears to be influenced by several environmental features associated with the ground layer. The species benefits from the reduction in litter cover and competing grass species that result from management actions such as prescribed burning. Understanding of the factors limiting this species, both at a local and regional scale, can be used to guide management of this ecotone habitat for both cockatoo grass and the survival of other species that depend on it.