Effects of Four Low-Intensity Burns Over 14 Years on the Floristics of a Blackbutt (Eucalyptus pilularis) Forest in Southern Queensland

Abstract

A grassy open forest of Eucalyptus pilularis Smith, E. saligna Smith, and other eucalypts, with an understorey of Allocasuarina torulosa (Aiton) L.A.S.Johnson and Acacia spp., was studied by belt transect for 14 years. The forest, north of Toowoomba in Queensland, was divided by a fire break into a non-burned section and a section that had a low-intensity prescribed burn through it four times over the observation period. Cover of herbaceous species, measured with the intercept method, and density of perennial species were recorded six times in the burned section and seven times in the non-burned section over the observation period. There was no difference between burning treatments in cover or density of the species sampled nor in their diversity (Shannon index) over this period. Classification analysis of data sets of the whole transect did not show clear groups and ordination of these data sets produced axes related to distribution of major species. These analyses indicated spatial variability along the transect as was apparent in the field. Total cover of the main grass species confirmed this variability, but also showed changes in parts of the transect over the period that were ascribed to changes in cover of the shrub layer. Data suggested that low-intensity burning stimulated ecesis of Acacia spp. but did not affect density of Allocasuarina torulosa (Aiton) L.A.S.Johnson and young eucalypts in this forest. Burning kept Lantana camara L. bushes small compared with not burning. Covers of the major grasses, Microlaena stipoides (Labill.) R.Br., Themeda triandra Forssk and Imperata cylindrica (L.) Rauschel, were not different between burning treatments. It appears that low-intensity prescribed burning produced less change over the 14 year period than did no burning. Change in the non-burned section may be attributed to encroachment of the exotic species Lantana camara. This situation is discussed in relation to recent plant succession theory.