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Snow-gum dieback update. By Dr. Matt Brookhouse

January 28, 2021

Dr Matthew Brookhouse extracting a sample

“Snow-gum dieback—the phenomenon quietly eating away at our high-elevation woodlands—is very poorly understood. For example, it is completely unclear why some stands of trees are being virtually wiped out, while others, only 500 metres away, are virtually untouched. Are there underlying differences between sites with differing dieback severity, or is dieback severity a product of patterns in the spread of the insect responsible? Even more fundamentally, we know very little about variability in the growth of snow gum over time. How, for example, does the species respond to year-to-year variation in temperature, snow-depth or drought? Similarly, on the insect front we know very little about the life-cycle and ecology of the ring-barker borer (Phoracantha mastersi) that appears responsible for the damage inflicted on the trees. When, for example, do the adults emerge from their pupal chambers to mate and lay the eggs that contain the next generation of borers?

Without answers to our most fundamental insect and forest ecological questions, appropriate management responses to snow-gum dieback will remain out of reach.

In late December 2020, our small team of ANU researchers commenced residency in the Perisher Valley. The aim was to conduct surveys of beetle species within stands affected and unaffected by dieback and, ultimately, trap live ring-barker borers. That trapping is multi-faceted, employing a combination of intercept and light traps. The latter appearing like a glowing jellyfish in stands throughout the Perisher Valley, Betts Camp, Spencers Creek and Charlotte Pass forests.

Intercept traps.

Light traps.

We have also commenced tree-ring sampling in the same stands. Using manual increment borers, we’ve extracted more than 200 samples from living and dead trees. Those samples will provide the basis for understanding not only long-term growth and tree physiology, but also any differences between growth on affected and unaffected sites.

Dr. Matthew Brookhouse extracting a core sample

Dr. Matthew Brookhouse extracting a core sample.

One of the critical, and often under-appreciated, elements of fieldwork is experiencing changing meteorological conditions and quietly observing the associated changes in the ecosystem. Understanding the connection between weather and forest and insect ecology may be a key part of adding to our conceptualisation of dieback. As many already know, the start of 2021 has been wet. A much-appreciated variation on last summer. Amid the changeable conditions our Odyssey jackets have proven time and again to be a critical piece of field gear to keep observations, samples and data coming in.

If you’re travelling in the Australian Alps this year and find yourself in a snow-gum forest, we ask two things. First, keep an eye out for signs of dieback and any longicorn beetles and report them via the SOSnowgum website. Second, love and respect them. Snow-gum forests have offered countless generations of Australians shelter and inspiration, are home to an astonishing array of flora and fauna, and are irreplaceable.”

Dr Matthew Brookhouse
Senior Lecturer
Fenner School of Environment and Society
ANU College of Science
The Australian National University

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