Our deepest sympathies go to everyone affected by the earthquake in Kumamoto. We hope you are staying safe amid the continuing aftershocks.
Post-earthquake inspections usually focus on buildings and walls, but trees are affected too. A tree that did not fall is not necessarily a tree that is fine: if the bond between roots and soil has loosened, it may fall in the next storm. This article covers how to inspect garden trees after an earthquake, what emergency care helps, and why the instinct to fell every tree near a slope deserves a second thought.
What an Earthquake Does to a Tree
A tree stands because its roots interlock with soil particles. Strong shaking loosens that interlock: fine roots tear, gaps open between the root ball and surrounding soil, and the whole tree may tilt toward its shallow-rooted side. A loosened tree also temporarily loses water uptake — in summer, wilting leaves can be the visible clue.
Inspection Steps
Step 1: Check the tilt
From a distance, compare the trunk angle against vertical references — a gate post, a building edge — and against pre-quake photos if you have them. A newly tilted tree means the roots have moved. Trees leaning toward a house or road should be referred to a professional without approaching.
Step 2: Read the ground at the base
- Arc-shaped cracks around the base: the most serious sign — the root ball has begun to rotate
- Heaved or sunken soil on one side: the roots are lifting
- Never test large trees by pushing or shaking them
Step 3: Check trunk and branches
Look for new vertical cracks in the trunk, split branch unions, and hanging broken branches caught in the canopy. Hanging branches drop in wind — keep people from walking beneath and have professionals remove them.
Trees on Slopes Are Also Retaining Structures
Before deciding to fell trees out of fear, know this: trees on a slope grip the soil with their roots and maintain pathways for water and air, supporting slope stability. In steep-slope failures, remaining tree roots are often what holds soil blocks in place and stops the failure from spreading.
Clear-felling a shaken slope can therefore backfire. Roots die and lose their grip several years after felling — and when heavy rain arrives then, the slope takes the water directly, with nothing holding it. Dangerous, badly leaning trees do need attention, but slope trees should be judged as a system of soil, water and roots, ideally with a forestry or landscaping professional.
Emergency Care: Do and Don’t
Do: support lightly tilted small trees with stakes and soft ties (do not winch them straight); cover exposed root gaps with soil to prevent drying; keep dated photo records. Standard three-point staking, cushioned where it meets the bark, tied at one-half to two-thirds of tree height, works well.
Don’t: pull large tilted trees upright with ropes or vehicles (it tears the remaining roots and is dangerous work); rush into heavy pruning or felling (severe pruning further stresses a root-damaged tree); seal ground cracks at the base with cement (it suffocates roots and traps water).
The First Year After the Quake
Root recovery takes years, not weeks. Watch weekly for tilt progression in the first month, water in the mornings during summer heat, and re-tighten stakes before typhoon season — a loosened root system plus storm winds is the classic combination that fells trees months after a quake. Winter reveals cracks and splits in bare branches, and next spring’s budding is the verdict: normal budding means roots are re-establishing, weak budding or dieback from branch tips calls for an arborist.
Summary
- Shaking loosens the root-soil bond; unfallen trees can still fall in later storms
- Inspect from a distance: tilt, arc-shaped cracks at the base, split branches, hanging limbs
- Slope trees are living retaining structures — clear-felling can destabilize the slope years later
- Light staking and records are fine as first aid; winching, heavy pruning and cement are not
- Give recovery a year of observation, with typhoon season as the critical checkpoint
Gardens and their trees will accompany the recovery for decades to come. We wish calm days back to the gardens of the affected region soon.