Bell miner associated dieback: nutrient cycling and herbivore crown damage in Eucalyptus propinqua

ABSTRACT

Various interactions appear to be involved in bell miner associated dieback (BMAD) of eucalypts. Native bell miner birds (Manorina melanophrys) defend the psyllids from predation by other birds while a dense understorey (notably Lantana camara) appears to favour the bell miners. The understory is likely to influence soil nutrient availability to the trees by changing the carbon to nitrogen ratio. We investigated the link between soil and leaf nutrient status and crown health as measured by crown index (CI) for Eucalyptus propinqua. Study sites included Bald Knob State Forest (SF), Donaldson SF, Mt Lindesay SF around Woodenbong and two locations on a Toonumbar private property in north-eastern New South Wales. Comparison of E. propinqua leaf macro- and micronutrient status using the ‘paired data sign test’ detected leaf nutrient differences between lightly and severely BMAD-affected tree crowns. Single and multivariate analysis investigated nutrient association with CI. Sign test results across all sites indicated that leaf iron content in trees with low CI (less healthy trees) was significantly higher (P = 0.01) than in healthy trees. In the three SFs the affected crowns also had significantly higher nitrogen to potassium ratios (P = 0.02). Other elements correlated with low CI were low boron (P = 0.06) across all sites and high zinc (P = 0.09) and low sodium values (P = 0.09) for Toonumbar sites. The correlation between soil and leaf nutrients was not significant and we found no significant correlations between soil nutrients and CIs. We did not detect any clear association between understorey (L. camara) and soil nutrients. During leaf sampling we found few psyllids but many concealer moth caterpillars. The scarcity of psyllids during sampling, inconclusive nutrient cycling results and nutrient correlations with CI were likely to be due to drought. Resampling under normal weather conditions with more typical organic matter decomposition rates is recommended.

KEYWORDS:

• Forest health
• nutrient cycling forest decline
• eucalypts
• Eucalyptus propinqua
• bell miners
• Manorina melanophrys
• psyllids
• Glycaspis sp
• lantana

Acknowledgements

We thank Dr Greg Elks who provided initial research data and ongoing advice over the duration of the project. We are grateful to Dr Wayne and Susan Somerville for allowing us to conduct some of the research on their property and for providing insight into the issues involved. Further we express thanks to Dan Allen and Forests NSW for granting us access to State Forests for this research. We also extend our thanks to the following people: Geoff Heagney and James O’Hara who shot down branches for leaf sampling, Maxine Dawes who helped with psyllid identification and the microscopy laboratory, Barbara Harrison who supported some laboratory work, Jim Morrison who gave advise and helped with leaf sampling and all other people and organisations that assisted us during the project’s execution.

ORCID

Peter Nageli http://orcid.org/0000-0002-0356-6072

Additional information

Funding

This project was initiated by National Parks and Wildlife Service with funding provided by the Australian Government’s Department of Agriculture, Fisheries and Forestry and the Department of Sustainability, Environment, Water, Population and Communities under the Caring for our Country initiative for the project ‘Mitigating the effects of bell miner–associated dieback in World Heritage Areas’ (A0000007972G).