Snow Gums and the Longicorn Beetle

The Australian Alps are home to endemic species that have evolved over long spans of time and isolation to suit extreme weather conditions (AANP, 2013). Sub-alpine woodlands are a type of ecological vegetation community (EVC) that are dominated by the endemic tree species Snow Gum (Eucalyptus pauciflora). Snow gums are the only tree species to grow at high altitudes (1300-1800m) and are recognisable by their short stature and twisted branches – that are pointed with the prevailing winds (Slattery, 2025). They combat the winter snow season in which water availability is locked up in snow and ice (Slattery, 2025). Snow gums face cold weather, strong winds and steep slopes (AANP, 2013). Hence, they have developed various survival adaptations such as rapid growing periods, moisture retaining leaves (small, thick and leathery) and seed dormancy. Furthermore, during early stages of growth, snow gums direct energy towards establishing strong and deep root systems (Slattery, 2025). 

DIEBACK

Dieback broadly refers to the decline of tree health, often over a population. (SOS, 2024). This process can occur due to senescence (old age) or environmental stressors (e.g. salinity, drought, fire or insect damage) (N. Schultz, personal communication, October 14, 2024). 

Historically, snow gums have experienced periodic dieback of upper branches. Initial reports in the 1990s revealed small stands of snow gum dieback on the Ramshead Range in Kosciuszko National Park. Aerial photography points to earlier signs of isolated dieback during the 1940s-1960s (SOS, 2024). However, significant and widespread dieback has only come to public attention in the last decade and increasingly ‘post-covid’. 

The Longicorn Beetle (Phoracantha spp.), also know as longhorn, is a native wood boring species that is thought to have lived harmoniously in lower elevation eucalypt forest previously (POW, 2023). Due to a number of factors, predominantly climate change, the beetle has risen to the sub-alpine in search of optimum conditions. They lay eggs on snow gums and the larvae (juvenile beetle) then bores through the bark (Jukes & Riley, 2024). The larvae feed on the cambium, xylem and phloem of the tree (ANU, 2021). Xylem is responsible for the transportation of water and nutrients from the soil, and phloem transports water and nutrients around the rest of the tree (similar to human veins and arteries). The cambium creates new layers of phloem and xylem (Tree Doctor, 2018). Therefore, longicorn beetle larvae are essentially ringbarking snow gums. Water and nutrient stores will not be transported to sustain the tree – this is why upper branches often show signs of dieback first (POW, 2023). The boring causes distinctive horizontal scars called galleries that are visible on the outer bark (ANU, 2021).

However, SOS (2024) contend that longicorn beetles are not absolutely linked to snow gum dieback:

“It is, for example, unclear whether wood-borer infestations precede or follow decline of trees within affected stands. Similarly, while the phenomenon has been widely reported as the consequence of a single species, that attribution remains anecdotal.”

Nevertheless, the longicorn beetle seems to be the most compelling reason for snow gum dieback.

A POSITIVELY REINFORCED CYCLE

Climate change is exacerbating the populations and impacts of longicorn beetles. Climate change is driving drought, warmer temperatures, reduced humidity and reduced snowfall resulting in moisture stress in sub-alpine woodlands (Olsson et al., 2024). Drought is rarely the primary cause of tree death but the susceptibility to other factors of decline is increased by drought (N. Schultz, personal communication, October 14, 2024). This is detrimental for snow gums given that longicorn beetles complete their life cycle up to 75% faster when tree are moisture stressed (NSW Government, 2019). POW, 2023 note that “whilst healthy, well-hydrated trees can control beetle populations, drier gums let the insect proliferate to unsustainable levels”. In this way, climate change is creating a positively reinforced cycle: increasing beetle populations results in more extensive dieback and death of snow gums, which will lessen carbon sequestration – ultimately driving climate change. 

IMPLICATIONS OF SNOW GUM LOSS

The loss of snow gums will cause ecological collapse in the Australian Alps. They provide various ecosystem services, a key example being the maintenance of hydrology in the Alps. Snow gums accumulate and capture wind-blown snow and have leaves that intercept moisture in the air. They regulate not only the flow of water in the catchment but also, indirectly, the timing of inflows (Olsson et al., 2024).

FUTURE ACTION

There are at present, no solutions for the longicorn beetle infestation (FotEM, 2023). Olsson et al. (2024) have suggested the radical solution of testing snow gum DNA strands in efforts to find a genotype that is beetle and drought resistant – of which the Australian National University (ANU) have now begun research on. The bottom line is that snow gum dieback requires further funding and research. The Snow Gum Declaration firstly calls for the recognition of snow gum woodlands as of vital importance to First Nations People, for the ecology of the Australian Alps and for the ecosystem services provided to Victoria’s water catchments (FotEM, 2023).  Friends of the Earth Melbourne (FotEM) (2023) also call for government funding towards assessing snow gum health across the Alps. 

Save Our Snow Gums (SOS) is a current research program coordinated by ANU to investigate dieback by mapping its extent:

“Snow-gum dieback has been observed across much of the Australian Alps. Each observation of dieback adds to our understanding and ability to respond. One of the most valuable ways to help is by reporting observations of dieback. While observations from remote locations are particularly valuable, all observations help” (SOS, 2024)

This is a form of citizen science where visitors to the Alps can record dieback through photos and observations. 

 

REFERENCES

Australian Alps National Parks [AANP]. (2013). Australian Alpine Education Kit. AANP. https://theaustralianalpsnationalparks.org/the-alps-partnership/education/

Australian National University [ANU]. (2021). Spotting snow-gum dieback: Guide for recording incidental observations for snow-gums exhibiting dieback symptoms using the ArcGIS Survey123 application. [PDF]. Fenner School of Environment & Society. https://theaustralianalpsnationalparks.org/wp-content/uploads/2021/09/Spotting-snow-gum-dieback-App-guide.pdf 

Clarke, M., & Davis, J. (2021). The sudden death of the snow gums. Abc.net.au; ABC News. https://www.abc.net.au/news/2021-03-10/sudden-death-of-snow-gums-longicorn-beetle/13226128

Friends of the Earth Melbourne [FotEM]. (2023). A rescue plan for the Snow Gums. FotEM. https://www.melbournefoe.org.au/a_rescue_plan_for_the_snow_gums 

Jukes, S. & Riley, K. (2024). Experiments with a dark pedagogy: Learning from/through temporality, climate change and species extinction (…and ghosts). Australian Journal of Environmental Education, 40(2), 108-127. https://doi.org/10.1017/aee.2024.12 

NSW Parks and Wildlife Service (2019). Snow gum dieback: Why is this happening?, In Resort round-up. State of NSW Department of Planning, Industry and Environment.

Olsson, R., Steiger, R., Nicotra, A. & Pittock, J. (2024). Our changing snowscapes: Climate change impacts and recommendations for the Australian Alps. Protect Our Winters. https://protectourwinters.org.au/our-changing-snowscapes/

Protect Our Winters [POW]. (2023). The Aussie Snow Gum: An Icon In Trouble. POW. https://protectourwinters.org.au/events/the-aussie-snow-gum-icon-trouble/ 

Save Our Snow gum [SOS]. (2024). Dieback. SOS. https://www.saveoursnowgum.org/dieback 

Slattery, D. (2025). Australian Alps: Kosciuszko, Alpine, and Namadgi National Parks (3rd ed.). CSIRO publishing. https://search.ebscohost.com/login.aspx?direct=true&AuthType=sso&db=nlebk&AN=4184018&site=ehost-live&scope=site&custid=univball&ebv=EB&ppid=pp_1 

Tree Doctors. (2018). Why trees have bark. Treedoctors.ca. https://treedoctors.ca/why-trees-have-bark