Late Holocene climate anomaly concurrent with fire activity and ecosystem shifts in the eastern Australian Highlands

Zoë A Thomas,Scott Mooney,Haidee Cadd,Andy Baker,Chris Turney,Larissa Schneider,Alan Hogg,Simon Haberle,Ken Green,Laura S Weyrich,Vilma Pérez,Nicole E Moore,Atun Zawadzki,Sarah J Kelloway,Stuart J Khan

doi:10.1016/j.scitotenv.2021.149542

Abstract

The alpine area of the Australian mainland is highly sensitive to climate and environmental change, and potentially vulnerable to ecosystem tipping points. Over the next two decades the Australian alpine region is predicted to experience temperature increases of at least 1 °C, coupled with a substantial decrease in snow cover. Extending the short instrumental record in these regions is imperative to put future change into context, and potentially provide analogues of warming. We reconstructed past temperatures, using a lipid biomarker palaeothermometer technique and mercury flux changes for the past 3500 years from the sediments of Club Lake, a high-altitude alpine tarn in the Snowy Mountains, southeastern Australia. Using a multi-proxy framework, including pollen and charcoal analyses, high-resolution geochemistry, and ancient microbial community composition, supported by high-resolution 210Pb and AMS 14C dating, we investigated local and regional ecological and environmental changes occurring in response to changes in temperature. We find the region experienced a general warming trend over the last 3500 years, with a pronounced climate anomaly occurring between 1000 and 1600 cal yrs. BP. Shifts in vegetation took place during this warm period, characterised by a decline in alpine species and an increase in open woodland taxa which co-occurred with an increase in regional fire activity. Given the narrow altitudinal band of Australian alpine vegetation, any future warming has the potential to result in the extinction of alpine species, including several endemic to the area, as treelines are driven to higher elevations. These findings suggest ongoing conservation efforts will be needed to protect the vulnerable alpine environments from the combined threats of climate changes, fire and invasive species.

Highlights

Alpine areas in Australia occupy only a small fraction of the largely flat continent, effectively making them ‘habitat islands’
To derive a proxy reconstruction of the air temperature at Club Lake over the late Holocene, we calculated a range of different branched Glycerol dialkyl glycerol tetraethers (GDGTs) calibrations, and compared these with the modern instrumental temperatures from Club Lake (Table 2, S2, S3 and Fig. S2)
To determine which calibration provides the most accurate representation of past temperatures at Club Lake, we compared the palaeotemperatures derived from the top 1 cm, which based on our age model represents sediment accumulation between 1932 and 2011, with the local instrumental record

Summary

Introduction

Alpine areas in Australia occupy only a small fraction of the largely flat continent, effectively making them ‘habitat islands’. The ecosystems of these areas are characterised by high biodiversity and endemism, with 212 species of vascular plants, 21 of which are endemic to the Snowy Mountains alpine area (Costin et al, 2000; Venn et al, 2017). The alpine area is only 135 km (Green and Stein, 2015). Despite this importance, these ecosystems are considered vulnerable to widespread phase changes that could fundamentally alter their dynamics (Elmendorf et al, 2012; Laurance et al, 2011). Alpine areas face uncertainty for their future longevity, with high vulnerability to anthropogenic and natural disturbances, and low rates of ecosystem resilience and recovery following disturbance (Hoffmann et al, 2019)

Methods

Results

Conclusion