What does a dying tree look like?
Start with the crown (the leafy top). A tree in trouble often thins out, with leaves that yellow, brown or drop out of season, or whole sections that stay bare when the rest leafs up.
Then the branches and trunk. Dead branches still on the tree, bark peeling or falling away, cracks and splits, and fungus growing from the wood all point to decay. WorkSafe's 2012 arboriculture code lists decay or rot, dead branches and hung-up branches (broken ones caught in the canopy) among the hazards arborists look for before any work.
Last, the ground. Soil cracking or heaving around the base, roots lifting on one side, and a lean that's new or getting worse are the signs to take most seriously, because they're about whether the tree stays standing.
Why do trees go downhill?
Christchurch City Council's list of causes makes a handy checklist. The biological ones include fungi, viruses, bacteria, nematodes (tiny soil worms) and wood and bark borers. Natural stresses include drought, flooding, extreme temperatures and mineral deficiencies.
Some trouble starts the day a tree goes in: planting too deep, poor quality stock, a lack of aftercare, or too little room for the roots. Those trees can struggle quietly for years before it shows.
Some common New Zealand trees have their own weak spots. The NZ Farm Forestry Association says radiata pine can get root rot if the ground becomes waterlogged, and some macrocarpa strains get canker, a fungal disease that can kill branches and leaders (the main upright stems). Possum browse can seriously damage and even kill pōhutukawa, and DOC counts cars parked on their roots among the threats. Kauri and the myrtle family face diseases of their own, covered in kauri dieback and myrtle rust.
Dead, dormant or just stressed?
A bare tree in winter may simply be deciduous. Compare it with last year's photos, or with the same kind of tree down the street.
The twig test helps. Pick a thin twig you can reach while standing on the ground and scrape a little bark off with your thumbnail. Bright green, moist wood underneath means that twig is alive. Brown and brittle means it's dead, but that's one twig, so try a few on different sides.
A stressed tree can pick up once the cause is dealt with, whether that's a dry summer, a new driveway over the roots or a waterlogged winter. A dead one won't, and its wood gets more brittle the longer it stands.
How to check your tree safely
Stand well back and look up
From outside the reach of any branch, look at the crown. Is it thinner than last year? Are some sections bare?
Walk around the trunk
From a safe distance, look for cracks, splits running down from a fork, loose bark, holes and fungus.
Look at the base and the ground
Check for cracked or lifting soil, exposed or broken roots, and any lean that's new.
Test a twig or two
Only twigs you can reach with both feet on the ground.
Take dated photos
Use the same spots each time, every few months. They show an arborist, the council and your insurer what has changed.
Make two calls before anything is cut
An arborist about the tree, and the council about the rules.
Signs that need an arborist soon
- A lean that's new, or getting worse
- Soil cracking or lifting around the base
- A split running down into the trunk
- Large dead branches over the house, the drive, a fence or where people sit
- Mushrooms or bracket fungus on the trunk or around its base
Dead wood over the house or a path?
Keep people, pets and cars out from under dead branches until an arborist has looked, because dead wood can let go without warning. Don't climb the tree, rest a ladder on it or try to pull branches down. If the tree is near a power line, stay away and call your lines company. In a storm, call 111 if anyone is in danger.
A dying tree near the house
Don't leave the decision to the next storm. The Insurance Council (ICNZ) says a tree owner may be liable if it's proven they were negligent in not removing rotten trees or ignored requests to remove them. It suggests assessing your trees before and after severe weather, and pruning or removing any that look weakened or damaged.
Auckland Emergency Management's storm advice points the same way: remove diseased or damaged branches to make trees more wind-resistant. ICNZ adds that trimming the odd branch may be safe, but big jobs that could damage a home or harm people are best left to an arborist.
Dead trees are harder to take down than live ones. WorkSafe's 2012 code calls for special care when felling dead trees, because parts may fall into the work area as the tree comes down. That's a big part of why a dead tree near the house is arborist work.
A dead notable tree still needs the council
Dead isn't the same as unprotected. ICNZ advises checking council rules before chopping, pruning or trimming a tree, including whether it's protected.
If the tree is a significant tree in Christchurch and it has died or failed structurally, a Tree Removal Certificate (P-024) goes to the council before it's felled, prepared by one of the council's listed technician arborists. In Auckland, removing a notable tree needs a resource consent, and even dead wood removal on one has to be done by a qualified arborist or it needs consent as well. Tauranga says a protected tree needs consent to remove it or prune it.
Look up your council's page under tree removal consents, and read notable trees for how to check a listing, before the job is booked.
What you can do, and what's arborist work
You can
- Watch the crown and the base, and keep dated photos
- Water deeply through dry spells, and mulch the root zone (keeping it off the trunk)
- Keep cars and building materials off the roots
- Prune small dead twigs you can reach with both feet on the ground, with hand tools
- Check whether the tree is listed before any work is booked
Leave to an arborist
- Dead branches above head height, or over the house
- Checking for decay inside the trunk
- Taking down a dead or dying tree
- Anything near a power line (the lines company first)
- The report a council asks for
Is my tree dead, dying or just having a hard year: what to do next
We'd photograph it, try the twig test on a few branches from the ground, and compare it with last year. If the dead wood hangs over the house or a path, we'd keep everyone clear and get an arborist out before the next windy spell. At the same time we'd check the council's list, because a dead tree can still need the council's sign-off before it comes down.
Want an arborist to look at it?
Tell us the job and your postcode, and a local arborist calls you to talk it through.