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DIEBACK

Dieback refers to the decline in health and, in severe cases, death of tree crowns. The term can refer to natural forest dynamics that lead to long-term species succession or to the outcome of dysfunction associated with disturbance or periodic stress. The latter usage generally reflects circumstances in which dieback has become problematic; that is when the rate of decline exceeds the regenerative capacity of the ecosystem. Those circumstances arise when novel forest disturbance processes or stressors predispose ecosystems to periodic decline in response to environmental (especially climatic) variability and biological agents such as fungi or insects. This latter form of dieback can lead to rapid and irreversible decline in the extent and quality of forest cover, substantially altering ecosystem services.

 

In Australia, problematic dieback events have arisen in a wide range of ecosystems. Familiar phenomena include dieback in jarrah (Eucalyptus marginata) forests, the woodlands and open forests of the New England tablelands, ongoing decline in association with the occurrence of bell miners (Manorina melanophrys) along the east coast of the continent, and recent death of manna gum (Eucalyptus viminalis) woodlands in the Monaro tablelands of south-east New South Wales associated with infestation by Gonipterus weevils.

 

Dieback of upper branches is relatively common in high-elevation snow-gum (Eucalyptus pauciflora) forests. However, outbreaks of problematic dieback are less frequent. Previously known as patch dieback, snow-gum dieback is characterised by evidence of infestation by wood-boring longicorn beetles. The phenomenon was first reported during the 1990s in isolated stands in the upper limits of the Ramshead Range and ridgelines alongside Prussian Creek in Kosciuszko National Park. Aerial photography indicates dieback first arose even earlier; within a twenty-year window during the 1940s to 1960s. Observations indicate that snow-gum dieback has recently expanded substantially.   

Although associated with evidence of wood-borers, the etiology of snow-gum dieback remains unclear. 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 insect species, that attribution remain anecdotal.

Current observations indicate that snow-gum dieback is present in stands of three snow-gum taxa—Eucalyptus pauciflora ssp. niphophila, Eucalyptus pauciflora ssp. debeuzevillei and Eucalyptus lacrimans. There are no confirmed observations of snow-gum dieback in the most widespread taxon, Eucalyptus pauciflora ssp. pauciflora.

Visit the ‘Report’ page to submit an observation of dieback.

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