How Windthrow Happens: Why Some Trees Uproot in Storms

How Soil Type Affects Windthrow

Different soils respond differently to root growth, rainfall and mechanical loading.

Shallow Soil

Where usable soil lies above rock, compacted subsoil or construction material, roots may be unable to develop sufficient depth. The tree may instead form a broad but relatively shallow root plate.

Compacted Soil

Compaction reduces the air spaces roots need and makes soil physically difficult to penetrate. Trees growing beside roads, car parks, construction areas and heavily used paths can be particularly affected.

Waterlogged Soil

Permanently or regularly waterlogged ground can restrict root oxygen and rooting depth, potentially reducing anchorage.

Loose or Recently Disturbed Soil

Recently filled or disturbed ground may not provide the same resistance as established, well-structured soil. The quality and depth of imported soil can significantly influence future stability.

Clay Soil

Clay can be strong when conditions are suitable, but its properties change with moisture. Some clay soils become softer when saturated and shrink during prolonged dry periods, potentially affecting the root-soil relationship.

Sandy or Freely Draining Soil

Free-draining soil may avoid prolonged waterlogging, but very loose soil may offer limited resistance if the root system is poorly developed or restricted.

An arborist therefore considers the complete rooting environment rather than assuming one soil type will always produce a particular outcome.

How Root Damage Can Lead to Windthrow

Roots are frequently damaged by activities that appear unrelated to tree stability. Excavation carried out several years before a storm may remove or weaken important structural roots without causing immediate changes in the canopy.

Potential causes include:

• Trenching for water, electricity, drainage or communications
• Excavating foundations
• Installing driveways and parking areas
• Lowering or raising surrounding ground levels
• Cutting roots during landscaping
• Repeated vehicle movement over the rooting area
• Construction storage beneath the canopy
• Mechanical stump removal beside a retained tree
• Damage caused by road or pavement works

A tree may continue producing normal foliage after losing major roots because the remaining root system still supplies enough water and nutrients. Its anchoring strength, however, may have been reduced.

This is why the history of the site is important during a tree assessment. Damage concealed below ground may only become apparent when the tree is subjected to exceptional wind loading.

How Root Decay Contributes to Uprooting

Decay can weaken structural roots and the lower trunk, reducing the tree’s capacity to transfer loads into the ground.

Root decay may develop following:

• Root injury
• Damage to the trunk base
• Long-term waterlogging
• Soil being piled against the trunk
• Infection by wood-decay organisms
• Historic construction damage
• Natural ageing processes

Possible indicators include:

• Fungal fruiting bodies near the trunk base
• Cavities around the root flare
• Areas of dead or loose bark
• Abnormal swelling
• Visible decay within exposed roots
• Movement between the trunk base and soil
• A decline in canopy vitality

The absence of fungal fruiting bodies does not prove that roots are sound, while their presence does not automatically mean that immediate failure is inevitable. Their significance depends on the organism, location, extent of decay and complete condition of the tree.

Why Tall Trees Can Be More Exposed to Wind Loading

As a tree increases in height, the canopy is exposed to stronger and less obstructed airflow. A taller tree also creates a longer lever between the canopy and the roots.

Height alone does not make a tree dangerous. Many tall trees develop substantial stems and root systems capable of supporting their size. However, risk may increase when significant height is combined with:

• Restricted rooting
• Root damage
• Saturated soil
• A disproportionately large canopy
• Sudden exposure
• Decay at the base
• A recent change in surrounding shelter

How Canopy Shape Influences Wind Loading

The canopy acts as the main surface against which the wind pushes. Its height, width, density and distribution affect the forces transferred into the trunk and roots.

Relevant features include:

• A broad canopy with substantial surface area
• Dense foliage during a storm
• A heavily one-sided crown
• Long, extended branches
• A top-heavy shape
• Multiple stems moving independently
• Climbing plants adding additional weight and surface area

Trees are flexible rather than rigid structures. Branches move, leaves reorientate and the canopy can reduce its resistance by bending with the wind. This natural flexibility helps dissipate some of the loading.

Failure becomes more likely when the force generated by the moving canopy exceeds the combined resistance of the stem, roots and soil.

Why Trees With Leaves May React Differently

A deciduous tree in full leaf generally presents more surface area to the wind than the same tree during winter. Summer storms can therefore produce substantial canopy loading, particularly when foliage is wet.

Winter storms remain highly significant because they can involve prolonged winds, saturated soils and repeated gusts. Evergreen species retain foliage throughout winter and may continue to experience a comparatively large wind-catching surface.

Whether a tree fails depends on the complete combination of canopy condition, exposure, root anchorage, soil and storm characteristics.

Why Sudden Exposure Can Destabilise Trees

Trees gradually adapt to the wind conditions they regularly experience. An open-grown tree exposed throughout its life may develop a broad root system, tapered trunk and growth pattern suited to that environment.

Trees growing within a dense group or woodland are partly sheltered by their neighbours. When surrounding trees are removed, the remaining trees may suddenly face wind speeds and directions they have not previously experienced.

Sudden exposure can result from:

• Development-related tree removal
• Woodland thinning
• Clearance of an adjacent site
• Storm failure of neighbouring trees
• Removal of a shelterbelt or hedge
• Demolition of a nearby building

The newly exposed trees may not yet have developed the stem strength, root distribution or canopy form associated with long-term open exposure.

This does not mean surrounding trees should never be removed. It means the potential effect on retained trees should be considered during planning and management.

How Topography Changes Wind Exposure

Wind does not travel evenly across every landscape. Hills, valleys, ridges, gaps between buildings and changes in ground level can accelerate or redirect airflow.

Trees may experience increased loading when situated:

• On exposed ridges
• Near the brow of a hill
• At the edge of open fields
• Within valleys that channel wind
• Between large buildings
• At exposed coastal or upland sites
• On newly created woodland edges

Local shelter can also be misleading. A tree that appears protected from one direction may be fully exposed when a storm approaches from an unusual angle.

Why Some Trees Uproot While Their Neighbours Remain Standing

Two adjacent trees may appear similar but have very different rooting environments and structural histories.

One tree may fail because it has:

• A shallower root system
• Undetected root decay
• Roots cut during historic construction
• A larger or more one-sided canopy
• A greater lean
• More direct exposure to the storm
• A waterlogged pocket of soil beneath it
• Less space for roots because of nearby foundations
• Previously lost neighbouring shelter

The surviving tree may simply possess better anchorage or experience a slightly different wind load. Storm damage can be highly localised, and small differences in soil, roots and gust direction can produce very different outcomes.

Does Tree Species Affect Windthrow Risk?

Species can influence rooting pattern, mature height, canopy form, wood properties and response to soil conditions. However, species should never be considered in isolation.

A species capable of developing good anchorage may still become unstable if its roots have been severed or confined. Equally, a species sometimes described as vulnerable to wind may remain stable when growing in suitable soil with adequate rooting space and long-term exposure.

Professional assessment should therefore consider:

• Species characteristics
• The individual tree’s form
• Its actual root environment
• Management history
• Site exposure
• Visible defects

Can Drought Make Windthrow More Likely Later?

Prolonged drought can reduce tree vitality, cause fine-root loss and place the tree under physiological stress. Dry soils may also crack or shrink, particularly where clay is present.

When heavy rain later returns, stressed or damaged roots may be exposed to rapidly changing soil conditions. If strong winds occur before the tree and soil system has recovered, vulnerability may be increased.

Drought does not mean a tree will necessarily uproot, but it can form part of a sequence of stresses involving:

• Reduced root vitality
• Canopy decline
• Pest or disease activity
• Soil shrinkage
• Subsequent waterlogging
• Storm loading

Can Previous Pruning Affect Wind Stability?

Appropriate pruning can be used to manage a specific structural issue, remove damaged branches or reduce excessive loading in selected circumstances. Poorly planned or excessive pruning can create additional problems.

Potential issues include:

• Removing too much live foliage
• Creating a severely imbalanced canopy
• Leaving large wounds
• Encouraging weakly attached regrowth
• Repeated topping
• Removing lower branches that contribute to normal trunk development

Topping a tree does not provide a reliable long-term solution to wind risk. It can result in large wounds and dense regrowth attached around the cut areas.

Where pruning is considered, our professional tree pruning is specified around the condition, structure and long-term management of the individual tree.

What Are the Warning Signs of Reduced Root Anchorage?

Windthrow can occur without obvious warning, especially during exceptional storms. However, certain features may justify professional assessment.

Warning signs include:

• Fresh cracks forming in the soil around the trunk
• The root plate lifting during windy conditions
• A newly developed or increasing lean
• Exposed, broken or severed roots
• Recent excavation close to the tree
• Fungal fruiting bodies around the base
• Cavities or decay at the root flare
• Soil movement on one side of the trunk
• A gap opening between the trunk base and ground
• Recent failure of neighbouring trees
• Sudden exposure following clearance work
• Unusual creaking accompanied by visible ground movement

A long-established lean is not necessarily evidence of imminent failure. Trees can adapt to inclined growth. A recent or increasing lean, particularly when accompanied by soil movement, is more concerning.

How Is Windthrow Risk Professionally Assessed?

An arborist cannot predict the precise moment when a tree will fail, but a professional assessment can identify observable factors that may influence stability.

The assessment may include:

1. Reviewing the Site History

The arborist may ask about:

• Previous construction or excavation
• Historic tree removal
• Changes in drainage
• Past storm damage
• Earlier tree reports
• Recent changes in lean or canopy condition

2. Assessing the Surrounding Area

The inspection considers:

• Buildings and structures
• Roads and footpaths
• Parking areas
• Public access
• Prevailing exposure
• Slopes and topography
• Changes in surrounding shelter

3. Examining the Canopy and Trunk

The arborist assesses tree form, vitality, branch distribution, previous failures, cracks, cavities and evidence of decay.

4. Examining the Root Flare

The visible structural roots and trunk base are checked for damage, cavities, fungal growth and movement.

5. Assessing the Soil and Rooting Environment

The arborist considers drainage, compaction, restricted rooting, excavation and recent changes to ground conditions.

6. Considering Further Investigation

Where the visual inspection identifies a significant uncertainty, further work may include:

• Root-collar investigation
• Soil assessment
• Specialist decay-detection testing
• Aerial inspection
• Monitoring ground or crack movement
• Reviewing construction and utility plans

TD Trees provides professional tree reports and surveys for individual trees, residential properties, commercial sites, estates and public-sector environments.

Can Windthrow Be Prevented?

No method can guarantee that a tree will remain standing during every possible storm. However, appropriate management can reduce avoidable risks and improve the resilience of trees and sites.

Preventative measures may include:

• Protecting rooting areas from excavation and compaction
• Providing sufficient rooting space when planting
• Maintaining suitable drainage
• Inspecting mature trees at proportionate intervals
• Reassessing trees after construction or severe weather
• Managing woodland edges carefully
• Avoiding abrupt removal of shelter where possible
• Using targeted pruning where a clear objective exists
• Removing trees where unacceptable risk cannot be reduced

Can Pruning Prevent a Tree From Uprooting?

Pruning may reduce canopy loading in particular situations, but it is not an automatic treatment for root instability.

Its suitability depends on:

• The cause of concern
• The amount and distribution of foliage
• Tree species and vitality
• The extent of any root damage
• Whether the tree can respond to pruning
• The surrounding level of risk

If the principal problem is extensive root decay or severe root severance, pruning may not provide an adequate long-term solution. Conversely, carefully specified reduction of a heavily loaded canopy may form part of a wider management plan.

When Might Tree Removal Be Recommended?

Removal may be advised where the root system has been substantially compromised and the risk cannot be reduced through proportionate management.

Examples may include:

• Active movement of the root plate
• Severe decay affecting structural roots
• Major root severance close to the trunk
• A recent and increasing lean
• Partial uprooting following a storm
• Multiple interacting structural defects
• A high-use area that cannot be restricted
• A tree already resting against another tree or structure

Where removal is necessary, our professional tree felling services include controlled dismantling and specialist methods for confined or complex sites.

What Should You Do After a Major Storm?

Do not immediately walk beneath or climb around damaged trees. Broken branches, split stems and partially uprooted trees can remain under considerable tension.

From a safe distance, look for:

• Fresh soil cracks
• Root plates that have lifted
• New or increased leaning
• Broken branches lodged in the canopy
• Split trunks or branch unions
• Trees resting against buildings, cables or neighbouring trees
• Recently exposed roots
• Movement during continuing winds

Where a tree appears unstable:

1. Keep people and animals away from the area.
2. Do not park vehicles beneath or beside the tree.
3. Do not attempt to cut tensioned branches or roots.
4. Avoid standing on or behind a lifted root plate.
5. Contact the relevant emergency service if there is an immediate public danger.
6. Arrange an assessment by a competent tree professional.

TD Trees provides specialist storm damage and emergency tree work for fallen, uprooted and structurally compromised trees.

Why Partially Uprooted Trees Are Particularly Dangerous

A partially uprooted tree may remain suspended by a combination of intact roots, neighbouring trees, branches, fences, cables or buildings. These forces can change without warning.

Hazards include:

• The tree completing its fall
• The root plate dropping back into the ground
• The trunk rolling or twisting
• Broken roots releasing stored tension
• Suspended branches falling
• Supporting trees failing under additional load
• The stem moving when cut

Cutting the trunk can suddenly change the balance of the entire system. Professional recovery work therefore requires a planned method, exclusion zones, appropriate equipment and clear communication between team members.

Can an Uprooted Tree Be Replanted?

Small, recently planted trees may sometimes be repositioned if sufficient roots remain intact and the original cause of failure can be addressed. The tree may require replanting at the correct depth, support, watering and ongoing monitoring.

Re-erecting a large mature tree is rarely straightforward. Significant roots may have torn, the tree may have lost much of its anchorage and the weight involved can make repositioning dangerous. Even where lifting is physically possible, long-term stability and survival may be uncertain.

The decision depends on:

• Tree size
• Extent of root damage
• Time since uprooting
• Soil conditions
• Available equipment
• Future support requirements
• Risk to people and property

What Happens to Windthrown Trees in Woodlands?

In a woodland setting, windthrow can have ecological as well as operational consequences. Fallen trunks, exposed soil and root plates create new habitats and alter light levels across the woodland floor.

Depending on management objectives, some windthrown material may be retained as deadwood while other trees are removed for access, safety, timber recovery or woodland regeneration.

Where multiple trees have failed, assessment should also consider whether remaining trees have become newly exposed and more vulnerable to subsequent storms.

How TD Trees Manages Windthrow and Storm-Damaged Trees

TD Tree & Land Services Ltd has provided professional arboricultural services since 2004 and is an Arboricultural Association Approved Contractor.

Our teams work across domestic, commercial and public-sector sites, including gardens, estates, roads, housing developments, hospitals, schools, woodland and transport infrastructure.

Depending on the situation, our approach may include:

• Establishing exclusion zones and immediate site safety
• Assessing root-plate movement and retained connections
• Identifying tension and compression within the tree
• Inspecting surrounding trees for secondary damage
• Planning access for arborists and machinery
• Using climbing, rigging, winching or crane-assisted techniques
• Sectionally dismantling trees in restricted areas
• Processing fallen timber and branches
• Removing or grinding remaining stumps
• Providing recommendations for retained trees

Operations are planned using site-specific risk assessments and appropriate method statements, with the work method selected according to the tree, site and surrounding hazards.

Frequently Asked Questions About Windthrow

What is the difference between windthrow and wind snap?

Windthrow occurs when the roots and surrounding soil fail, allowing the tree to uproot or overturn. Wind snap occurs when the trunk or a major stem breaks while the root system remains largely anchored.

Does windthrow mean the tree’s roots were unhealthy?

Not necessarily. A healthy root system can be overwhelmed by exceptional wind loading, particularly in saturated or shallow soil. However, root damage, decay and restricted rooting can increase vulnerability.

Can a completely healthy tree uproot in a storm?

Yes. Severe wind can exceed the resistance of an otherwise healthy tree and its soil. Tree health and mechanical stability are related, but they are not the same thing.

Are leaning trees more likely to uproot?

Some leaning trees are well adapted and remain stable for many years. Concern increases when the lean is recent, worsening or accompanied by cracked soil, root-plate movement or damaged roots.

Why do trees fall after the strongest wind has passed?

Repeated rocking can progressively damage roots and surrounding soil. A weakened tree may then fail during a later gust or after the storm, particularly if the root plate has already moved.

Can a tree uproot without falling completely?

Yes. Partial windthrow can leave a tree leaning while some roots remain attached. This can be highly unstable because the tree may complete its fall later.

Does waterlogged ground always make trees dangerous?

No. Many trees tolerate wet conditions and remain stable. Waterlogging becomes more significant when combined with shallow rooting, poor drainage, root defects, high exposure or substantial canopy loading.

Should I reduce the height of every large tree before a storm?

No. Routine height reduction is not appropriate for every tree and poorly specified pruning can create additional problems. Work should respond to the condition, structure and surroundings of the individual tree.

Can tree roots be inspected without digging them up?

An arborist can assess visible roots, the root flare, soil conditions, site history and signs of movement. Where further information is needed, careful root-collar investigation or other specialist methods may be recommended.

What should I do if the ground moves around a tree in strong wind?

Move away from the tree and keep others clear. Do not approach the base or stand within the likely fall area. Arrange an urgent professional assessment once it is safe to do so.

Can a windthrown tree damage underground services?

Yes. A rotating root plate can lift or disturb pipes, drains, cables, paving and nearby structures. The full site should be assessed before recovery work begins.

Should neighbouring trees be inspected after one tree uproots?

Yes, particularly where they share similar soil conditions or have suddenly lost shelter. The same storm may also have damaged roots or branches that are not immediately obvious.

Arrange a Professional Assessment After Storm Damage

Windthrow results from an interaction between wind, canopy loading, roots, soil, exposure and tree condition. The fact that a tree is tall or leaning does not by itself prove that it is dangerous, while a tree that looks healthy may still have compromised anchorage below ground.

Professional assessment can identify observable concerns, explain the available management options and determine whether monitoring, pruning, further investigation or removal is appropriate.

TD Trees provides professional tree assessments, storm response, consultancy and tree surgery for domestic, commercial and public-sector clients across Edinburgh, Central Scotland, the Scottish Borders, Northumberland and surrounding areas.

To discuss a leaning, storm-damaged or potentially unstable tree, request a tailored quotation from TD Trees.