We've recently joined with research partners and colleagues to form the High Country Dieback Network. The network is aiming to build stronger partnerships between land manages and researchers, and build a collaborative research approach for understanding dieback processes in snow gum and lower-elevation forests.
Current lab members and activities
We're working to identify local drivers and ultimate causes of snow-gum dieback with the aim of guiding long-term management. Our current research is focussed on resolving a few seemingly basic questions - where is dieback occurring, what insect is responsible, and why is it happening now?
Understanding tree vulnerability
To understand why dieback is happening now, we need to know exactly when it occurred in the past. Tree rings offer a pathway to answer these questions. Using samples collected over decades, we can date long-dead trees, opening a window to the past. Using an array of tree-ring properties, we aim to reconstruct the history of dieback and identify the external events that lead to outbreaks.
While working to understand the past, we're also working on understanding the vulnerability of trees in the present day. We've deployed a network of sensors in Kosciuszko and Namadgi National Parks that are monitoring diurnal and seasonal variations in growth and moisture status of tree tissues with the goal of identifying the factors that affect infestation of stems by wood-boring beetles.
The role of landscape determinants and disturbance
Very few quantitative data exist on the severity of current dieback outbreaks throughout the Australian Alps. In the absence of those data, mapping of the extent, and rate of spread is impossible. Similarly, the lack of data impairs our ability to understand the potential role of factors such as topography and disturbance. The remote terrain on which snow-gum stands occur means the ground-based surveys offer limited value in our dieback studies. To overcome this limitation we are turning to high-resolution remote sensing to identify change in snow-gum cover with time.
Identifying and understanding the culprit
Although the damage that leads to dieback is consistent with longicorn (Phoracantha sp.) beetles, the species-level identity of the insect driver of snow-gum dieback remains unclear. Using an array of trapping techniques and experiments, we aim to identify the insect species involved. While interesting in itself, identification of the species is just the start - we need to know when the insects are out and how this corresponds with the vulnerability of the trees they attack. We also need to identify the key factors that determine selection of host trees and survival of larvae.
In addition to the relentless task of checking traps daily and night-time experiments, the entomological aspects of our work involve nigh-time surveys that, as shown below, offer insights to the diversity of Australia's invertebrate diversity
Previous mapping indicates that outbreaks of snow-gum dieback have occurred on a smaller scale in the Perisher Valley and Ramshead Range. The dead stems left behind provide an opportunity to understand the events that precipitate outbreaks. Systematic sampling of dieback-affected stems during 2021-22 will aim to resolve the precise timing of dieback, in doing so, ideally give us a chance to identify potential causes. This work is being completed by Honours student Michael Jones.
The wood-borer genus associated with snow-gum dieback is known to respond to drought stress. Specifically, the larvae of the borer stand a far better chance of surviving in dry bark. As we work towards an understanding pf how bark and wood moisture content affects the insects responsible for snow-gum dieback, we are also working on techniques to generate calibration data for tissue water deficit models. The techniques are varies, drawing upon detailed stem measurements of radial expansion and contraction, sap flow and moisture content, and leaf-level measures of water potential. This work is supported by greenhouse-based experimentation of snow-gum seedlings and is being completed by Honours student Aaron Midson.