Fire ecology and fire management for the conservation of plant species and vegetation communities in a National Park in northern NSW, Australia

Abstract

Frequent fires have been suggested to result in a decline in plant species composition and structure in Australian plant communities. This is especially apparent in regions in northern NSW thought to have had a history of frequent low intensity fires, primarily due to accidental ignitions and ignited to promote grass for cattle grazing. The aim of this study was to investigate recent fire regimes and their impacts on the vegetation composition and structure to address future fire management planning. The study was undertaken in Guy Fawkes River National Park in northern NSW, through compiling a fire history by integrating hard-copy fire records and filling gaps with multi-temporal satellite imagery. The 25-year fire history provided the stratification variables for a survey of the current vegetation patterns in relation to a number of fire frequency attributes including number of fires, shortest inter-fire interval and time since last fire. The results from the vegetation study demonstrated that shrub and tree species richness declined with increasing number of fires and shorter inter-fire intervals. This was particularly evident in the Tablelands area of the study region where the fire history was more varied and the environmental variation more constrained. The study also revealed a sharp decline in the abundance of woody shrubs and an accompanying simplification of the structure of the vegetation community with increasing number of fires and shorter intervals between fires. Complementary soil seed bank studies were undertaken to compare the impacts of high and low fire frequency. A reduced abundance of shrub species was apparent in the seed bank of sites with a history of frequent fires. Shrub species, such as Acacia irrorata, were predominantly found in the seed bank of long unburnt sites. The information from these studies was used to develop a management framework based on fire thresholds for species and vegetation community conservation. Plant species data compiled from these plus other studies provided information on regenerative mechanisms following fire, the time to reproductive maturity and longevity. Fire thresholds were determined for the majority of communities in the study region, above and below which plant species were likely to decline. This framework of fire thresholds was used to identify areas where the minimum recommended time period between fires had been exceeded in the 2000/01 fire season. Five vegetation communities were identified with 80% or more of the total area exceeding the recommended fire threshold, indicating that a decline in plant species richness was possible due to recent fire regimes. The study provided the first fire ecology study in this region and a baseline on which to build future research. The integration of fire ecology information into spatially explicit fire management guidelines was demonstrated, providing the basis for future planning for the preservation of plant species and vegetation communities in large conservation areas.