Multiple lines of evidence infer centurial-scale habitat change and resilience in a threatened plant species at Mount Dangar, Hunter Valley, New South Wales

Abstract

Context Populations of the threatened plant Acacia dangarensis at Mount Dangar (Hunter Valley, New South Wales) may best be managed by recognising centurial, rather than decadal, change in habitat. Aim Multiple data sources have been used to explore the hypothesis that above-ground presence of A. dangarensis is driven by centurial-scale cycles in climate (wet–dry phases) and fire. Methods Current-day floristic composition is contrasted with that documented by pre- and post-1900 botanical explorers for A. dangarensis and the fire-sensitive Callitris glaucophylla. Examination of fire history, oral recollections, rainfall and specimen collection databases, and radiocarbon (14C) and dendrochronological analyses of A. dangarensis have been used to build an ecological history of Mount Dangar. Key results There is no evidence of A. dangarensis occurring on Mount Dangar between 1825 (the first documented exploration) and 1979 (the first collection). Furthermore, historical wet–dry cycles where sufficient fuel was likely to have accumulated to propagate fire (required for seed germination) infer that the species may have last germinated from the seed bank c. 1730, but senesced prior to 1825. Our results suggest that a major fire during the extremely dry Austral summer of 1957–1958 killed most of the then dominant C. glaucophylla individuals. This fire followed 7–10 years of well above-average rainfall, allowing sufficient fuels to accumulate for fire to heat the soil and again release Acacia seed from dormancy. Conclusions Long-term resilience in A. dangarensis is highlighted irrespective of fire irregularity and recurrent drought that have occurred over at least the past 195 years. Implications Centurial-scale cycles in climate and fire appear to drive above-ground presence in this species. When present, occasional fruiting events may be sufficient to maintain the seed bank until suitable climatic conditions again favour a major wildfire event and subsequent seedling recruitment.