El Niño Summer in the Australian Alps: What does it mean for Visitors and Snow Gum Dieback?

Written by Oliver M. Medd

After three years of wetter and cooler conditions for eastern Australia, conditions have shifted with above-average temperatures likely for the remainder of spring. The snow season has come to an early finish, which means it is time for summer activities in the Australian Alps – think hiking, mountain biking, fishing, and camping. The BOM recently declared that this summer will see both El Niño and positive Indian Ocean Dipole (IOD) conditions, meaning we might be in for the hottest, driest weather on record for the Snowies.

While a warmer and drier spring and summer has the potential to bring a host of visitors to the Australian Alps, it may also have consequences for the current dieback phenomenon unfolding in the area. Dieback research in the Australian Alps has grown progressively since 2019. This season sees a suite of new projects and aspects being explored by members of the Australian National University’s Save Our Snow Gum research group.

El Niño and visiting the Australian Alps

The warmer conditions associated with this year’s El Niño event are likely to bring increased risk of heatwaves, bushfires and drought—particularly because this year El Niño’s coincides with a positive IOD event. These phenomena bring new challenges to all of us as we seek to work or simply enjoy the region over the summer; increasing the risk of heat stroke and other heat-related injuries.

“Neither El Niño nor positive IOD conditions guarantee hot weather in the Australian alps, but when they occur at the same time it is extremely likely that they bring an unusually hot summer” said Dr Georgy Falster, a climate researcher at the Australian National University (and mountain lover, often out in the Snowies in her Mont Moondance tent).

Dr Falster said that with the combination of El Niño and positive IOD conditions, “the upcoming summer won’t just be hot, but also dry – every positive IOD year on record has brought below-average rainfall to the Australian alps. This dryness means the land surface heats up even more, and also increases the risk of bushfires in the area”. Falster adds “we can’t forget that this summer’s El Niño and positive IOD conditions sit on top of the long-term trend of global warming, making hot summers in the alps increasingly likely”.

Summer temperatures in the Snowy Mountain region spanning back until 1971, showing both a steady increase in average summer temperatures, and separate/combined El Niño and Positive IOD events. Credit: Dr. Georgy Falster @fishmittns

Like those venturing into the Alps for leisure such as hiking and mountain biking, as researchers we will be keeping a close eye on the combined challenges of warmer temperatures and intense sun exposure at high elevation. In addition to typical practices like increasing the water we carry and making use of shade and sunscreen, we’re also planning ahead to respond if the increased risk of fire leads to an emergency situation.

What does an El Niño & positive IOD summer mean for dieback?

Since at least 2008, snow-gum (Eucalyptus pauciflora spp. niphophila) woodlands have been in a state of decline. Known as snow-gum dieback, the phenomenon is associated with canopy and eventual entire-tree death. Snow-gum dieback is particularly prevalent within the ski-fields of Kosciuszko National Park, where the majority of the observations have been made.

Researchers in the field collecting data and samples as part of the Save Our Snow Gum team. Image credit: Sabina Aitken @sabinaa.photography

Snow-gum dieback is associated with damage attributed to the ring-barker borer (Phoracantha mastersi). The species has a longevity of ~3 years, living out most of its life in a larval form, feeding on the inner bark and outer wood of snow-gums, effectively ring-barking affected trees. Once in adult form, individuals appear to survive for only a few weeks. During that time, they must reproduce. Research to date is ambiguous as to whether the insect plays a role in promoting forest dieback, or simply takes advantage of stands that are already in decline. Nevertheless, the ring-barker borer is one of a suite of native longicorn beetles present in high-elevation woodlands, and is particularly common in dieback affected woodlands.  Long-time readers of the Mont blog may remember a series of posts regarding snow-gum dieback made by Dr. Matthew Brookhouse, which can be read here.

 Left: A snow gum in the early to middle stages of dieback, with large puckering holes in the trunk caused by feeding beetle larvae. Right: An adult longicorn wood-borer beetle nestled into the broken bark of a snow gum. Image credit: Sabina Aitken @sabinaa.photography

While little is known about the ring-barker borer, knowledge of closely related species that have plagued eucalypt plantations overseas suggests that this season’s forecast conditions may mean an increase in insect activity this summer. Three years of nocturnal field surveys have revealed an apparent association with day-time temperatures and reproductive behaviours in the following evening. That is, a sequence of days with above-average temperature maxima, and sustained evening temperatures, often brings increased mating behaviours by ring-barker borers.

If previous year’s observations hold true this summer, conditions associated with El Niño and a positive IOD will increase insect reproduction and dispersal, increasing the number of larvae infesting trees in subsequent seasons and, in turn, driving greater rates of infestation in subsequent years. Depending on the role played by the ring-barker borer, this summer may drive an expansion and intensification of dieback for years to come. Worryingly, climate change associated warming means these ideal beetle-breeding conditions will continue to get more common, possibly accelerating snow gum decline.

A stand of dieback affected snow gums in Kosciuszko National Park. Image credit: Sabina Aitken @sabinaa.photography

This is where you come in.

With temperatures more pleasant later into the evenings, there may be a greater likelihood that, like us researchers, you’ll be out enjoying the alpine region in the coming season. That will, of course, increase the chances of both spotting dieback and, in late-January to March, the beetles themselves.

On our website, www.saveoursnowgum.org, you can access images of dieback and longicorns, and upload your observations of both to our database, joining the growing number of citizen scientists involved with this project. The Save Our Snow Gums team will be out there too. We’ll be catching insects, monitoring tree moisture status and collecting tree cores to expand our understanding of the nature of the current and previous dieback events.

Image credit: Sabina Aitken @sabinaa.photography

Finally, a bit about me : My name is Oliver Medd, and I am a PhD student at the ANU, working to better understand what is driving both the current and any previous dieback events. I will be conducting further field research with Dr. Matthew Brookhouse and other researchers, and over the coming months l will be presenting a series of posts in this blog that’ll cover the breadth of our research in the Alps.

The next post will take a look at research in the field as we try to catch and study the beetles during mating season, and further observe the dieback outbreak. Keep an eye out and join the mailing list (if you haven’t already) to read my next post when it comes out.

Also, visit our website at www.saveoursnowgum.org to find our more and to contact us with any questions.

Author: Oliver M. Medd @merlin_research

Editors/Commenters: Dr. Georgy Falster @fishmittns, Dr. Matthew Brookhouse

Photos: Sabina Aitken @sabinaa.photography