Preliminary observations on the mortality of Allosyncarpia ternata stems on the Arnhem Land Plateau, northern Australia

Summary

Allosyncarpia ternata is the sole dominant tree of a rainforest community endemic to the western edge of the Arnhem Land Plateau. The hypothesis that Allosyncarpia forests are currently retreating due to unfavourable fire regimes was tested by tagging 352 Allosyncarpia stems (> 1 cm DBH) on the perimeter of an isolated circular patch of rainforest in a remote part of Kakadu National Park. Four years since tagging (1989–1993), in which at least two wildfires were known to have burnt rainforest, the overall mortality rate of relocated stems (N=289) was 36%. The highest mortality occurred in the 1–5 cm DBH size class (75%). For relocated stems > 5 cm DBH the mortality rate was 14%.

A transect study in late July 1993 revealed that midday ground surface temperature below Allosyncarpia canopies was about 10° lower than ground surface temperature in the surrounding savanna. Death of Allosyncarpia canopy trees therefore have a significant impact on the maximum temperature of the forest floor, and this may explain the previously observed restriction of Allosyncarpia seedlings to beneath the canopy of adults.