MUNMARLARY REVISITED - RESPONSE OF A NORTH AUSTRALIAN EUCALYPTUS-TETRODONTA SAVANNA PROTECTED FROM FIRE FOR 20 YEARS

A comparison was made between the total density of tree species record ed on three 1 ha plots that have been protected from fire for 20 years , and from three surrounding sites that have been subjected to the amb ient fire regime. Both unburnt plots and ambient sites were in a lowla nd coastal Eucalyptus tetrodonta savanna in Kakadu National Park. Fire protection resulted in a substantial increase in the number of saplin gs (16 times more than ambient), poles (five times more than ambient) and trees (2.5 times more than ambient), but slightly fewer (7%) sprou ts than ambient. Of the 32 species recorded in the six 0.2 ha samples, only nine species could legitimately be analysed using Chi-squared an alysis to test for differences in the density of sprouts and saplings between unburnt and ambient samples; eight of these species had signif icantly different distributions. Typically the unburnt samples had a g reater number of saplings compared to ambient conditions, but fewer sp routs. Eucalyptus miniata showed no significant difference in the dens ity of sprouts and saplings between the unburnt and ambient samples. C hi-squared analyses of the frequency distribution among four size clas ses (sprouts, saplings, poles and trees) was possible for six species. The results for five of these species mirrored the findings of the co mparison between sprouts and saplings. However, the fan palm Livistona humilus, which typically forms a component of the mid-layer in E. tet rodonta savannas, was found to have a large number of sprouts on the u nburnt samples and a complete absence of stems in any of the other siz e classes. Dead L. humilus stems attested to the former occurrence of larger size classes of this species on the unburnt plots. No rainfores t species were recorded in the unburnt samples. Minor differences in s pecies composition between unburnt and ambient samples are thought to reflect sampling effects. The results of this study are consistent wit h the conclusions of an earlier study at the same site which also conc luded that rainforest tree species do not readily colonize unburnt Euc alyptus savanna.