AQF Level 5 Consulting Arborist Julian Parry and TCAA President Jim McArdle report on a silent war: suspected poisoning and vandalism threatening the NSW capital’s urban forest.
A tree dies quietly. The leaves don’t fall first. Instead, they dry out and hang on, brown and brittle, clinging to branches that were green only weeks earlier. Sometimes there are small drill holes in the trunk. Sometimes the bark has been cut away in a thin ring around the stem. Occasionally there’s a faint chemical smell in the soil near the base of the tree. By the time an arborist is called, it’s often too late.
Across Sydney’s suburbs, mature canopy trees that have stood for decades, sometimes more than a century, are dying under circumstances arborists suspect are not natural. According to those working closest to the problem, the scale of the problem may be greater than most people realise.
Suspected cases every week
Julian Parry, a consulting arborist and director of Arbor Pride Tree Services, spends much of his working week inspecting trees across Sydney. He estimates he assesses around 50 properties each week, ranging from residential blocks to redevelopment sites and council inspections.
It’s a level of exposure that provides a window into the health of Sydney’s urban forest, and Parry’s comments on what he is seeing are alarming.
“In my consulting work across Sydney, I now encounter between five and 10 suspected tree-poisoning cases every week,” he said.
Over the course of a year, that could equate to hundreds of suspected incidents.
TCAA arborists want to assist the government in reducing tree loss through illegal means, and while many arborists privately acknowledge the trend, few cases ever lead to prosecutions.
The reason is simple: proving who poisoned a tree is difficult.
The pattern arborists recognise
After inspecting thousands of sites, arborists say the pattern is often familiar.
It starts with a property changing ownership. Development plans are proposed, and soon afterwards, a large tree suddenly begins to decline.
The symptoms can appear quickly. Rows of drill holes may appear in the trunk or herbicides may be injected into the tree’s vascular system. In other cases, bark is stripped away around the trunk – a method known as girdling or ringbarking.
The effect is the same: the tree slowly starves, and within months may become structurally unsafe. Once it’s declared hazardous, it can often be legally removed.
“By the time an arborist is asked to inspect the tree, the damage is usually irreversible,” Parry said.
The economics
Large trees can complicate development. Their root systems can limit excavation, their canopies may restrict building envelopes, and protected trees often require costly design changes or engineering solutions. Removing them can dramatically increase a site’s development potential.
In Sydney’s property market, that difference can be worth hundreds of thousands – or even millions – of dollars.
Penalties for illegal tree removal, however, are often lower. The biodiversity act states a fine of $200,000 and two years gaol, while the local council will issue fines starting at $3000. In serious cases prosecuted under environmental legislation, penalties can be greater, but prosecutions remain rare.
When the potential financial gain vastly outweighs the likely penalty, arborists say the deterrent effect disappears.
“If the value of removing a tree is measured in millions of dollars and the penalty is only a few thousand, the risk becomes a business calculation,” said TCAA President Jim McArdle.
Signs of deliberate poisoning
Arborists trained to assess tree health often recognise indications of deliberate interference. Common indicators include:
* Drill holes of uniform depth in the trunk;
* holes spaced around the circumference of the tree;
* damage to buttress roots or exposed primary roots;
* chemical staining around injection points;
* rapid dehydration of foliage while leaves remain attached; and
* vertical cracking in vascular tissue exposing internal wood.
Substances suspected in poisoning incidents can include herbicides, petroleum products, salt compounds and other contaminants introduced into the tree’s vascular system.
But arborists must also rule out natural causes such as root failure, lightning strikes, soil movement or prolonged water stress before reaching conclusions.
A living remnant forest
Many of the large trees affected are found across Sydney’s North Shore – suburbs such as Wahroonga, Pymble and Turramurra.
These areas once supported extensive forest ecosystems, including Blue Gum High Forest and Sydney Turpentine–Ironbark Forest, both now listed as endangered ecological communities. Many mature trees standing in suburban streets and backyards are surviving remnants of those original forests, and when one of those trees is lost, arborists say it represents more than the removal of a landscape feature. It’s the disappearance of a living remnant of Sydney’s ecological history.
Other forms of tree vandalism
Tree poisoning is not the only threat. Across bushland reserves, parks and campsites, arborists also see widespread physical damage to trees. Carving, cutting and chainsaw scarring are common forms of vandalism. The cambium layer beneath the bark – responsible for transporting nutrients through the tree – is relatively soft and vulnerable. Damage to this layer can interrupt the tree’s vascular system and eventually kill it.
Some trees carry historic scars left by Aboriginal cultural practices or early surveyors marking routes through bushland, but modern vandalism bears little resemblance to these cultural artefacts and often results in long-term damage.
The ecological value of deadwood
Another lesser-known environmental issue is the removal of deadwood from bushland areas for firewood.
While fallen timber may appear lifeless, it plays a crucial ecological role, providing:
* Habitat for insects and fungi;
* shelter for reptiles and small mammals;
* nesting and roosting sites for birds; and
* nutrient recycling within forest ecosystems.
Removing these natural structures can disrupt entire microhabitats. In some jurisdictions, collecting wood from protected areas can attract large penalties.
Why most cases go unreported
Despite the frequency with which arborists say they encounter suspicious tree deaths, most incidents are never formally investigated. Establishing proof requires chemical testing, forensic investigation and evidence linking the act to a specific individual. Without witnesses, cases can be difficult to pursue. The NSW Environment Protection Authority (EPA) regulates pesticide use and can investigate reports of chemical misuse or environmental damage, and this may involve site inspections, laboratory testing, interviews with nearby residents, and letter drops to surrounding properties.
Arborists say many incidents are never reported in the first place.
A problem hiding in plain sight
According to AQF Level 5 Consulting Arborist Julian Parry and McArdle, the most concerning trend may be the public’s growing acceptance of the issue. Where neighbours once reacted with outrage when mature trees died suddenly, arborists now report a more resigned response.
“People are starting to treat it as normal,” said McArdle. “That’s the most worrying part. If deliberate tree destruction becomes routine, the pressure that once discouraged it begins to fade.”
Protection
Sydney’s urban forest provides more than visual appeal. Large canopy trees reduce urban heat, provide wildlife habitat, absorb stormwater and improve air quality. They also shape the character of neighbourhoods.
Arborists argue that protecting these trees requires stronger enforcement, better reporting of suspected poisoning, and penalties that reflect the true environmental value of mature canopy trees. Trees are worthy of CCTV security to reduce these incidents and EPA regulators are able to assist, because once a tree that took a century to grow is destroyed, it cannot be replaced.
The loss is measured not in years but in generations.
Event
The TCAA has an AQF 3 and AQF 5 event at Hornsby RSL on May 1 from 9.00am to 3.00pm. The risk assessment methodology of VTRA and AANZAA valuation will be introduced and discussed, and a book launch for Arboristry in Australia and licensing will be included. Members can attend for free, and non-members for $300. Contact Admin@tcaa.com.au or info@mcardlearborist.com.au for more info. There are 40 places available.
To learn more of the TCAA, visit tcaa.com.au.
