Effects of fire frequency on plant species composition of sandstone communities in the Sydney region: Inter‐fire interval and time‐since‐fire

Abstract

Abstract Fire frequency is the number of fires experienced by a particular community within a given time period. This concept can potentially be resolved into a number of interacting variables, including: time since the most recent fire, the length of the inter‐fire intervals, and the variability of the length of the inter‐fire intervals. We estimated the effects of these three variables on the floristic composition of 65 samples from dry sclerophyll vegetation with different fire histories in Brisbane Water, Ku‐ring‐gai Chase and Royal National Parks near Sydney.Our analyses suggest that fire frequency may account for about 60% of the floristic variation among our samples. They confirm the hypothesis that the recent (<30 years) fire frequency produces effects on floristic composition of fire‐prone communities that can recognizably be attributed both to the time since the most recent fire and to the length of the intervals between fires. These effects are equal in magnitude but are different in the nature of the floristic variation they are associated with. Increasing time‐since‐fire is associated with a decline in the evenness of fire‐tolerant species, indicating that fewer of these species come to dominate the community in the prolonged absence of fire. Herbs and small shrubs decrease in abundance, while larger shrubs increase in abundance. Inter‐fire intervals of decreasing length are associated with a decrease in the evenness of the fire‐sensitive species, particularly those large Proteaceae shrubs that often dominate the community biomass in dry sclerophyll shrublands of southeastern Australia.Furthermore, the variation associated with inter‐fire intervals is not necessarily solely related to the shortest inter‐fire interval, but is related to combinations of inter‐fire intervals through time. Thus, increasing variability of the length of the inter‐fire intervals is associated with an increase in the species richness of both fire‐sensitive and fire‐tolerant species, implying that it may be variation of the inter‐fire intervals through time that is primarily responsible for maintaining the presence of a wide variety of plant species in a particular community. Our results also suggest that the floristic variation associated with different inter‐fire intervals decreases with increasing time‐since‐fire.