Climate, not Aboriginal landscape burning, controlled the historical demography and distribution of fire-sensitive conifer populations across Australia

Abstract

Climate and fire are the key environmental factors that shape the distribution and demography of plant populations in Australia. Because of limited palaeoecological records in this arid continent, however, it is unclear as to which factor impacted vegetation more strongly, and what were the roles of fire regime changes owing to human activity and megafaunal extinction (since ca 50 kya). To address these questions, we analysed historical genetic, demographic and distributional changes in a widespread conifer species complex that paradoxically grows in fire-prone regions, yet is very sensitive to fire. Genetic demographic analysis showed that the arid populations experienced strong bottlenecks, consistent with range contractions during the Last Glacial Maximum (ca 20 kya) predicted by species distribution models. In southern temperate regions, the population sizes were estimated to have been mostly stable, followed by some expansion coinciding with climate amelioration at the end of the last glacial period. By contrast, in the flammable tropical savannahs, where fire risk is the highest, demographic analysis failed to detect significant population bottlenecks. Collectively, these results suggest that the impact of climate change overwhelmed any modifications to fire regimes by Aboriginal landscape burning and megafaunal extinction, a finding that probably also applies to other fire-prone vegetation across Australia.

Multilocus phylogeography reveals nested endemism in a gecko across the monsoonal tropics of Australia

“…Woinarski et al 2007). However, more recent modelling of potential distributions during the LGM suggests localized persistence of some monsoonal taxa , and greater stability than for related species from the adjacent arid zone (Sakaguchi et al 2013; but see Kearns et al 2014).…”

“…), and greater stability than for related species from the adjacent arid zone (Sakaguchi et al . ; but see Kearns et al . ).…”

Two climate‐sensitive tree‐ring chronologies from Arnhem Land, monsoonal Australia

“…The genus Callitris is a widespread, evergreen and taxonomically complex drought‐tolerant group of species (Piggins & Bruhl ; Sakaguchi et al . ) in the family Curpressaceae. There are around 13 species endemic to Australia (Farjon ), and an additional species restricted to New Caledonia.…”

Effect of landscape fires on the demography of the endangered New Caledonian conifer Callitris sulcata

“…It is possible that the species was more widespread prior to human colonisation, but was subsequently eliminated from all but the remote valleys in the infertile south of the island. This biogeographic hypothesis could be tested by undertaking genetic analyses of the populations, as has been done for the Callitris glaucophylla complex across Australia (Sakaguchi et al, 2013).…”