Response of Callitris intratropica R.T. Baker and H.G. Smith to fire protection, Murgenella, northern Australia

Pattern analysis of stems > 10 cm d.b.h. on 514 one-tenth ha quadrats showed that Callitris intratropica has a clumped distribution throughout the more uniformly distributed Eucalyptus forests at Murgenella in Northwest Arnhem Land. Callitris clumps are typically located on sites with sandy soils. Eucalypts occur within Callitris clumps. Fire suppression over the past 18 years has allowed some C. intratropica to establish on Eucalyptus forest sites with fine textured soils It is argued that distribution of Callitris preceding fire management was controlled by the interactive effects of fire, soils and understorey vegetation. High grass fuel loads (and thus intense fires), and competition are thought to have previously limited establishment of C intratropica on fine textured soils. Early dry season burning by Aboriginals may also have been important in limiting fire intensities and accumulation of fuel in Callitris stands. Dry electrical storms commonly cause fires prior to the summer rains. Such wildfires did not completely kill stands of Callitris saplings or trees at Murgenella. Survivors were found to be significantly bigger and to have thicker bark than the dead stems. Sapling size is related to age and density, thus fire may be an important mechanism in thinning heavily stocked stands. The continuous regeneration of Callitris and Eucalyptus is in marked contrast to the inhibition of Pinus caribaea recruitment following fire protection in the monsoonal neotropics. The lack of seral tree species in northern Australia suggests an equilibrium between forest distribution and the physical environment.