Introduction

Bell Miner Associated Dieback (BMAD) currently occurs through sclerophyll forests on public and private lands in New South Wales, Victoria and Queensland. These forests are regionally important for plant and animal conservation, water catchment management, tourism and the production of honey and timber. This form of dieback is of national significance as it is spreading through forest ecosystems in eastern Australia.
 

The Nature of the Issue

Eucalypt dieback, strongly associated with sap feeding insects called psyllids, is sometimes associated with the native Bell miner or bellbird (Manoria melanophrys) and has become common in some parts of the bird’s range. Bell miners are a natural part of some eucalypt ecosystems and normally have a functional role similar to other honeyeaters. However, increases in Bell miner populations and their distribution, in addition to other factors such as tree stress, psyllid infestation, dense forest understories, forest structure as well as weed invasion, drought, logging, pasture improvement, soil nutrient changes, frost and changing fire and grazing regimes have all been implicated in the spread of dieback. The outward expression of BMAD is generally characterised by:

  • trees and outer branches dead or dying, in bad cases high epicormic leaf production and discoloured leaves;
  • high populations of psyllids and other sap-sucking insects;
  • high numbers of Bell miners, their aggressive territorial behaviour, driving away insectivorous birds that would otherwise help to control insect numbers;
  • alteration of the forest structure: canopy and midstories depleted with grassy and wet and dry sclerophyll understoreys replaced by dense shrubby vegetation, often associated with Lantana invasion.

Dieback occurs within wet and dry sclerophyll forest communities. The forests most susceptible to dieback are those dominated by Dunn’s white gum (Eucalyptus dunnii), Sydney blue gum (E. saligna), flooded gum (E. grandis), grey ironbark (E. siderophloia), narrow leaved White Mahogany (E. acmenoides), grey gum (E. punctata), and grey ironbark (E. paniculata). There is also evidence that some normally non-susceptible dry sclerophyll types e.g spotted gum (E. maculata) and blackbutt (E. pilularis) may be affected when they occur alongside susceptible forest types.
The potential impacts of BMAD on forest productivity and biodiversity cannot be overstated.

The actual impacts on native species has not been quantified, however the potential impacts on conservation values include:

  • Extreme degradation of forest ecosystems in World Heritage listed National Parks such as Border Ranges NP, Murray Scrub and Dome Mountain in Toonumbar NP, Bungdoozle and Cambridge Plateau in Richmond Range NP, Mt Nothofagus NP, Kooreelah NP, Mt Clunie NP and the Blue Mountains and Woollemi N.P.
  • Major disruption in ecosystem function, and reduction in diversity and abundance of threatened flora and fauna species including Dunn's White Gum (Eucalyptus dunni), Yellow Bellied Glider (Petaurus australis), and Rufous Bettong (Aepyprymnus rufescena) across all land tenures,
  • Increased weed invasion and associated displacement of native forest species.
  • Impacts on forest productivity can be severe. Dieback defoliates the crown, ultimately leading to the death of standing trees. Not only do the standing trees die, but the lack of foliage and flowering and subsequent fruiting, reduce and eventually eliminate the seed production necessary for forest regeneration. Dense understorey development (primarily Lantana weed invasion in northern NSW and Cissus in the south) continues with little over-storey and reduced species competition. Reduced eucalypt flowering directly impacts on honey production and on bird species and populations that compete with Bell miners.