Effects of high frequency fire on floristic composition and abundance in a fire-prone heathland near Sydney

The effect of high frequency fire regimes on a coastal heathland north of Sydney was examined. Plant community composition and species frequency and density (of a subset of species) were compared among sites burnt by either one, two or three fires in the period 1988-1990 inclusive. Constrained ordination indicated that number of fires had a significant effect on floristic composition. Site variables also had a significant effect on floristics and frequency and accounted for a larger proportion of variation than did number of fires. Analyses of deviance indicated that frequency in 13 species was unaffected by fire regimes or site factors. Site factors significantly affected frequency in 42 species. Frequency in seven species was significantly affected by fire regimes (no site effect). In six of these, frequency was lower in areas subjected to either two or three fires compared to one fire. Three of these species were obligate seeders. Frequency in the other species (a herbaceous resprouter) was significantly higher in the area subjected to two fires. There was no significant effect of fire on species richness. Densities of seven out of a subset of eight species were also significantly affected by fire (two obligate seeder spp.) and site factors (four spp.), Significantly lower densities were related to multiple fires. The study indicated that regimes of frequent fire can deplete populations of some heathland species with the dominant shrub species, Banksia ericifolia L.f., being most affected.