EFFECTS OF HIGH-FREQUENCY FIRE ON FLORISTIC COMPOSITION AND ABUNDANCEIN 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 frequ ency and density (of a subset of species) were compared among sites bu rnt by either one, two or three fires in the period 1988-1990 inclusiv e. Constrained ordination indicated that number of fires had a signifi cant effect on floristic composition. Site variables also had a signif icant effect on floristics and frequency and accounted for a larger pr oportion of variation than did number of fires. Analyses of deviance i ndicated that frequency in 13 species was unaffected by fire regimes o r site factors. Site factors significantly affected frequency in 42 sp ecies. Frequency in seven species was significantly affected by fire r egimes (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 subjecte d to two fires. There was no significant effect of fire on species ric hness. Densities of seven out of a subset of eight species were also s ignificantly affected by fire (two obligate seeder spp.) and site fact ors (four spp.), Significantly lower densities were related to multipl e 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.