Australasian Plant Conservation
Originally published in Australasian Plant Conservation 20(4) March - May 2012, p 11-13
Mitigating the effects of forest eucalypt dieback associated with psyllids and bell miners in World Heritage Areas
Bryony M. Horton
National Parks and Wildlife Service, NSW Office of Environment and Heritage, Coffs Harbour NSW.
Symptoms of bell miner associated dieback: tree death at Border Loop, Border Ranges National Park.
Symptoms of bell miner associated dieback: crown thinning and branch death of eucalypts at Wallaby Creek, Tooloom National Park.
Dieback and decline
Dieback is a widespread problem affecting individual trees, woodlands and forests across Australia. Dieback refers to the deterioration in the health of the tree crown from which recovery can occur. Progressive, gradual deterioration in overall tree vigour leading to premature death is known as decline. Both can occur as the result of interacting biotic and abiotic factors producing a series of stress-response events. Causes have been attributed to drought, pathogens, herbivory, ecological feedbacks, and altered land management especially in relation to fire and grazing (Heatwole and Lowman 1986, Close et al. 2009).
Forest eucalypt dieback associated with psyllids and bell miners
In eastern Australia, eucalypt dieback associated with psyllids and bell miners, known as bell miner associated dieback (BMAD), is a serious issue. Large areas of forest from Victoria to southern Queensland, on both public and private land are under threat. The detrimental impacts include loss of habitat, biodiversity, and forest productivity, as well as altered ecological processes, all of which threaten the integrity of these iconic eucalypt ecosystems. In NSW BMAD is recognised as a Key Threatening Process under the Threatened Species Conservation Act 1995 (http://www.environment.nsw.gov.au/determinations/bellminerfd.htm).
Forest eucalypt dieback associated with psyllids and bell miners is a complex ecological problem with many interacting factors (Wardell-Johnson et al. 2005). Psyllids are a group of sap sucking, lerp forming, foliage invertebrates. Psyllid outbreaks may occur in response to nutrient enriched new growth (due to tree stress or high soil nutrients), climatic factors, or predator and parasitoid interactions (Paine and Hanlon 2010, Stone et al. 2010).
Bell Miners feed on the lerp (the sugary coating on the nymphal psyllid) but often do not eat the psyllid, allowing the psyllid population to remain unchecked. Bell miners are aggressively territorial, fending off other bird species that would otherwise predate on the psyllids. Bell miners require a specific habitat and forest structure for nesting, including a relatively dense midstorey 2 – 5 m in height (Stone 2005). In disturbed forests, the invasive weed of national significance Lantana camara often provides these conditions. In many forests the interactions between psyllids and bell miners leads to crown dieback, evident through canopy thinning and branch death, and can ultimately result in tree death.
World Heritage Areas under threat
BMAD is threatening the eucalypt communities in the Gondwana Rainforests of Australia and Greater Blue Mountains World Heritage Areas (WHAs). The Gondwana Rainforests of Australia extends from the central coast of NSW to south-eastern Queensland and the Greater Blue Mountains Area lies west of Sydney in NSW. These WHAs are of special conservation significance recognised internationally for their outstanding universal values (http://www.environment.gov.au/heritage/places/world/index.html).
The project ‘Mitigating the effects of Bell Miner Associated Dieback’ is funded under the Commonwealth Government’s Caring for Our Country grants scheme. This project aims to address the threat of BMAD to the Gondwana Rainforests and Greater Blue Mountains WHAs. This will be achieved through undertaking actions to treat and prevent BMAD in combination with research, monitoring and spatial analysis, to better understand the process and occurrence of eucalypt dieback throughout the WHAs.
The project consists of two major components. The first component focuses on the threat of BMAD by answering fundamental questions such as:
- How much eucalypt forest in these WHAs is affected or at risk?
- Which type of forests are affected or at risk?
- Where are these affected forests located?
- How badly affected are they?
The answers to these questions will enhance our understanding of the issue and help prioritise areas for management. Qualitative questionaries to land managers and aerial photo interpretation of high-resolution digital aerial imagery with ground validation will be used to address these questions. Repeating the mapping and questionnaires in the future will help to assess changes in dieback over time.
The second component utilises adaptive management to answer the questions:
- How can we prevent and treat BMAD?
- Which of these options work and which don’t?
- What is the most appropriate management in different situations and places?
The main management method being trialled is bell miner habitat modification by weed control or fire, along with limited psyllid control through tree injection with insecticide. Where lantana occurs, weed control removes the dense midstorey and allows a more open forest structure to establish and native composition to be restored (Yeates and Schooler 2011, Somerville et al. 2011). Fire also modifies forest structure, and is often more effective at the landscape scale. Fire alters ecosystem process such as nutrient cycling, as well as creating a large disturbance event from which succession in many different parts of the ecosystem can occur. These may also be important factors for mitigating dieback.
Treated sites will be surveyed before treatment and then monitored annually following treatment for 2-5 years. Surveys of fixed quadrats across different sites and landscape positions will allow an assessment of changes in bell miner and psyllid populations, and any improvement in tree health. The data will also be used to look for patterns that may indicate which forests and species are affected or susceptible and at risk.
This project is applying the principles of adaptive management to address the issue of BMAD. We are identifying long-term options to mitigate dieback and restore forest health. In other areas we are attempting to prevent the deterioration of forest health into a state of dieback by actively identifying forests that are susceptible and at risk, and implementing proactive management. Management tools include the use of fire, weed control, and invertebrate control that aim to modify bell miner habitat and reduce bell miner numbers, or reduce psyllid abundance. Fire may also re-instate ecological processes, such as nutrient cycling, which help to maintain healthy forests. The outcomes of this project will assist with prioritising areas for management, identifying which management tools should be applied, and build our knowledge on the process of eucalypt dieback and the key elements that are important for the maintenance of forest health.
Close, D.C., Davidson, N.J., Johnson, D.W., Abrams, M.D., Hart, S.C., Lunt, I. D., Archibald, R., Horton, B.M. and Adams, M.A. (2009) ‘Premature decline of Eucalyptus and altered ecosystem processes in the absence of fire in some Australian forests’, Botanical Review, 75: 191-202.
Heatwole, H. and Lowman, M. (1986) Dieback, death of an Australian landscape, Sydney, NSW: Reed Books.
Paine, T.D. and Hanlon, C.C. (2010) ‘Integration of tactics for management of Eucalyptus herbivores: influence of moisture and nitrogen fertilization on red gum lerp psyllid colonization’, Entomologia Experimentalis Et Applicata, 137: 290-295.
Somerville, S., Somerville, W. and Coyle, R. (2011) ‘Regenerating native forest using splatter gun techniques to remove Lantana’, Ecological Management & Restoration, 12: 164-174.
Stone, C. (2005) ‘Bell-miner associated dieback at the tree crown scale: a multi-trophic process’, Australian Forestry, 68: 237-241.
Stone, C., Chesnut, K., Penman, T. and Nichols, D. (2010) ‘Waterlogging increases the infestation level of the pest psyllid Creiis lituratus on Eucalyptus dunnii’, Australian Forestry, 73: 98-105.
Wardell-Johnson, G., Stone, C., Recher, H. and Lynch, A.J.J. (2005) ‘A review of eucalypt dieback associated with bell miner habitat in south-eastern Australia’, Australian Forestry, 68: 231.
Yeates, A.G. and Schooler, S.S. (2011) ‘Influence of Lantana camara and its removal on tree dynamics in a recently burnt wet sclerophyll forest in Northern NSW’, Ecological Management & Restoration, 12: 236-241.