Long term context for bushfires in inhabited and uninhabited landscapes: A Holocene record from Kangaroo Island (Karti/Karta), South Australia

Abstract

Understanding the drivers of long-term fire regime change is critical for conserving lives, cultural heritage, and biodiversity across the globe. Kangaroo Island (Karti/Karta), Australia, presents a rare opportunity to examine long-term fire dynamics in response to climate in the absence of people, following the cessation of permanent human occupation during the mid-Holocene. Previous research suggested the loss of anthropogenic landscape management led to increased late Holocene fire activity, a hypothesis debated due to uncertainties in the palaeoenvironmental record. We present a new 7000-year pollen and charcoal record and re-evaluate archaeological evidence using Bayesian phase modelling to assess the relative roles of anthropogenic activity and climate on fire dynamics. This reappraisal suggests that human activity ceased between 6.2 and 5.0 cal ka BP (95.4% CI), closely aligning with a major shift in vegetation composition, however not coinciding with an immediate increase in fire activity. Prior to ∼5.5 cal ka BP we find evidence for open Casuarinaceae woodland with elongate charcoal particles, consistent with burning of fine fuels. After ∼5.5 cal ka BP, a transition to Myrtaceae-dominated woodland with a shrub-dominated midstorey and less-elongate charcoal suggests a shift towards burning of more woody vegetation. In the late Holocene, fire activity intensified amid pronounced drying and heightened rainfall variability. We argue that the increase in fire activity was primarily a consequence of lower and more variable rainfall, exacerbated by the absence of human influence. These findings highlight the combined influence of climate, vegetation and people on fire activity, with implications for future fire management.