Plant rarity in fire-prone dry sclerophyll communities

Abstract

Understanding the responses of rare species to altered fire disturbance regimes is an ongoing challenge for ecologists. We asked: are there associations between fire regimes and plant rarity across different vegetation communities? We combined 62 years of fire history records with vegetation surveys of 86 sites across three different dry sclerophyll vegetation communities in Booderee National Park, south-east Australia to: (1) compare associations between species richness and rare species richness with fire regimes, (2) test whether fire regimes influence the proportion of rare species present in an assemblage, and (3) examine whether rare species are associated with particular fire response traits and life history. We also sought to determine if different rarity categorisations influence the associations between fire regimes and plant rarity. We categorised plant rarity using three standard definitions; species' abundance, species' distribution, and Rabinowitz's measure of rarity, which considers a species' abundance, distribution and habitat specificity. We found that total species richness was negatively associated with short fire intervals but positively associated with time since fire and fire frequency in woodland communities. Total species richness was also positively associated with short fire intervals in forest communities. However, rare species richness was not associated with fire when categorised via abundance or distribution. Using Rabinowitz's measure of rarity, the proportion of rare species present was negatively associated with fire frequency in forest communities but positively associated with fire frequency in woodland communities. We found that rare species classified by all three measures of rarity exhibited no difference in fire response traits and serotiny compared to species not classified as rare. Rare species based on abundance differed to species not classified as rare across each life history category, while species rare by distribution differed in preferences for seed storage location. Our findings suggest that species categorised as rare by Rabinowitz's definition of rarity are the most sensitive to the effects of fire regimes. Nevertheless, the paucity of responses observed between rare species with fire regimes in a fire-prone ecosystem suggests that other biotic drivers may play a greater role in influencing the rarity of a species in this system.