Fire severity is an important driver of land snail declines after the black summer bushfires in Australia

Abstract

Many ecosystems globally evolved with fire. However, there is a gap in our knowledge regarding the effect of fires on less mobile invertebrates. Land snails in Australia are a diverse group with a high level of endemism, but we understand very little of their ecology, especially how they are affected by large fires.We studied the short-term (one year after a fire event) response of 1) land snail species composition, 2) snail abundances, and 3) impacts on 18 priority species to an unprecedented large fire event throughout south-eastern Australia in 2019/2020 (Black Summer). Our study ranged over >100,000 km2, surveying162 sites. Our study revealed that land snail species composition changed significantly depending on fire severity class, regardless of habitat type (rainforest or eucalypt forest) or climate. Medium and high severity fire caused snail abundance to decline significantly, with micro-snails being more sensitive to medium and high severity fires. Abundance dropped by 75 % and 64 % for micro-, and macro-snails respectively, but low severity fire did not have a significant impact on abundance. For most priority species, fires affected more than half of their known extent of occurrence although most species were found in all fire severities. However, severity category was an important driver in determining the probability of occurrence of priority species. To conserve Australia's land snail species, we must know how they are affected by disturbances. Our results suggest that the total area and severity of fires will determine the impact of fires on land snails.