Eucalypt health surveillance - ACT & NSW Southern Tablelands sightings

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Purpose

For use as a reference collection to monitor Eucalypt health in the ACT and the NSW Southern Tablelands. Impacts on Eucalypts include: climate change, drought, plant pathogens and pests, and high severity fires.

The condition of the Eucalypt canopy, leaves, buds, and bark (particularly on smooth barks) are good indicators of plant health. Unhealthy Eucalypts may be affected by a number of factors. For example: Bell Miner - Psyllid dieback, Phytophthora dieback, Drought-induced fissure - Long-horned beetle dieback, Drought-induced xylem embolism and cavitation (hydraulic failure), Ginger tree syndrome, Novel fire regime from climate change and/or weed invasion, and Rural dieback. In urban remnant vegetation, environmental weeds also contribute to Eucalypt decline, e.g. English Ivy.

Eucalypts include the following genera: Eucalyptus, Corymbia and Angophora.

Eucalypts are keystone species

Eucalypts are keystone species for many Australian ecosystems. Planted Eucalypts are also strongly associated with insect and bird diversity and this can assist bird populations in adjacent woodland or forest. Hence why this project includes planted Eucalypts as well as those that are naturally occurring.

Eucalypt canopies and fine roots affect soil properties, via rainfall through fall, rainfall stem flow, leaf and bark litter, extensive fine root turnover, and mycorrhizae. This has a significant effect on nutrient cycling and understorey vegetation patterns.

How to add your Eucalypt sightings

Add your Eucalypt sightings to the project collection by selecting the star icon at the top right of the sighting page (to the left of the edit option) on your desktop computer, and scroll thru the collection list to find the collection title 'Eucalypt health surveillance - ACT & NSW Southern Tablelands'. Don't forget to fill out all the data fields for the Eucalypt sighting: number of the species (i.e. number in the immediate area, usually within 20m, or if uncertain set the number to 1), tree health, height, number of hollows, circumference, canopy radius (if asked), planted or naturally occurring, and use the public comments field for extra plant health information (e.g. disturbances, pests, site history), and for noting different age classes or plant health status of the number recorded.

Helpful id guides: The EUCLID app, and Native Eucalypts of Victoria and Tasmania - South-eastern Australia by Dean Nicolle.

Blog 27th May 2024

There are enough Eucalypt sightings (3,077) in the ACT Southern Tablelands to start seeing some patterns with Eucalypt health.

Method: 1,145 of the 3,077 sightings, comprising 70+ species, have been added to this Eucalypt health surveillance project. Most of the sightings are from the last 10 years. The sightings added have a good image of the tree canopy and/or a good image of the trunk (for smooth bark species). Some also have close up images of the condition of the leaves, oil glands and venation. Each sighting was assessed based on the associated data fields, comments, and examining the images. Several sightings triggered the automatic NatureMapr timeline function which made comparison overtime easier, e.g., https://canberra.naturemapr.org/sightings/timeline/24452

The sightings show examples of:

'Ginger tree syndrome' in E.lacrimans, and E.pauciflora subsp. pauciflora.
Drought induced trunk fissures and/or longicorn beetle larvae damage in E.pauciflora subsp. pauciflora
Pysllid-lerp infestations in young E.blakelyi.
Post-drought leaf damage in E.macroryhncha subsp. macrorhyncha from leaf blight.
Rural dieback in E.melliodora and E.blakelyi.

Other species specific drought and fire related observations:

Drought tolerance of species consistent with the literature, i.e., lower water potential (Ψ) tolerated in more drought tolerant species. The drought tolerance based on Ψ at zero turgor: E.melliodora > E.globulus > E.pauciflora > E.viminalis.
A naturalised population of the rare and endangered E.parvula has shown to be resilient to very high severity fire (the 2003 fire).
Very high severity fires in early 2020, near the end of the drought killed trunk and branch meristems on trunk/branch resprouting capable species, so those effected Eucalypts were only showing lignotuber resprouting, e.g., E.dives, E.dalrympleana subsp. dalrympleana, and E.viminalis subsp. viminalis.

General observations:

Resistance and resilience of most species to the 2018-19 drought (consistent with the literature: ability of many Eucalypt species to shut-down when drought occurs, i.e., resistance, and ability to rapidly absorb and transpire water when it becomes available again, i.e., resilience).
Patchy branch death (hydraullic failure) in a range of species but mainly at marginal sites for the species.
Tall trees in marginal habitat suffered more patchy branch death from the 2018-19 drought than shorter trees of the same species (consistent with the literature).
Sites with less water stress had less examples of patchy branch death. This included many large trees in urban open space. The exception was large trees in some rural dieback areas.
Subgenus Eucalyptus (with the exception of E.rossii) had more patchy branch death than subgenus Symphomyrtus (consistent with the literature).

Patchy branch death - when is it a problem? :

Some patchy branch death is to be expected due to drought.
Large amounts correspond to a significant loss in the ability to transport water in the xylem, i.e., a large loss in hydraulic conductivity.
As drought worsens, water potential becomes more negative, i.e., increased xylem tension and risk of cavitation, and branch death.
Ψ50 is the water potential where there is a 50% loss in hydraulic conductivity.
Ψ88 is the water potential where there is a 88% loss in hydraulic conductivity.
At Ψ50, Eucalypts are in trouble but can recover. At Ψ88 it is lethal. Interestingly, for conifers the lethal threshold can be Ψ50.
Ψ50 may not present as 50% of the crown dying. However a large amount of patchy branch death indicates significant hydraulic failure.
Recovery after patchy branch death is via resproutung on unaffected parts of branches, or resprouting on the trunk or lignotuber, depending on the Eucalypt species.
Patchy branch death is also caused by high and very high severity fire if the meristems are killed and epicormic growth cannot resprout on the branches, or even the trunk. Then for the Eucalypt to survive it needs to be a species that also resprouts from the base, via a lignotuber.

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