Why One Side of Your Tree Is Dying in Calgary (Causes & What to Do)

When one side of a tree begins to die while the rest looks healthy, it can be confusing and alarming. This pattern—called unilateral decline—is one of the most common issues Calgary homeowners face. It often appears suddenly in spring or gradually over several seasons. Because Calgary trees deal with drought, chinooks, heavy winds, and poor soil, partial decline is especially widespread here.

At Calgary Tree Care, our ISA Certified and TRAQ Qualified Arborists assess trees with one-sided decline year-round. This guide explains the causes, the warning signs, and what Calgary homeowners should do to protect their trees.

Why One Side of a Tree Dies

Partial tree decline indicates that something is affecting only a portion of the canopy or root system. The top reasons include:

1. Root Damage on One Side

The most common cause is root damage beneath the dying side of the tree. Because each section of the canopy is supported by specific roots, any injury to one section will show up directly above it.

Root damage often happens due to:
• Construction or trenching
• Irrigation installation
• New patios, driveways, or walkways
• Soil compaction from vehicles or foot traffic
• Grade changes
• Root rot or fungal infection

If roots die, the canopy above will decline.

2. Sunscald or Heat Scorch

Calgary’s intense sun combined with dry chinook winds can burn one side of a tree, especially the south or southwest exposure.

Symptoms include:
• Bark cracking or peeling
• Brown, dead branches on the exposed side
• Needles or leaves burnt or curled
• Discoloured bark that later dies

Young trees, fruit trees, and spruce are especially vulnerable.

3. Winter Desiccation

Dry winter winds pull moisture from needles and buds while frozen soil prevents water uptake. This is often worst on the wind-exposed side.

Look for:
• Browning on the south or windward side
• Dieback in late winter or early spring
• Healthy growth on the protected side

Spruce, cedars, and pines frequently show one-sided winter burn.

4. Pest or Disease Localized to One Area

Many pest infestations begin on a specific branch or canopy section.

Common Calgary examples include:
• Spider mites on hot, dry sides
• Birch leafminer on one-exposed quadrant
• Poplar borers attacking one stem
• Cytospora canker on one section of spruce
• Fire blight spreading down one branch of apple/crabapple trees

If the pest or disease spreads, more of the canopy will decline.

5. Mechanical Damage

Anything that wounds bark or branches may cause one-sided decline.

Common causes:
• Lawn equipment impacts
• String trimmers cutting bark
• Vehicles or machinery
• Kids’ swings or hammocks tied too tightly
• Animal chewing

These wounds disrupt nutrient flow to the affected side.

6. Soil Problems Affecting Only Part of the Root Zone

Calgary’s clay soils often dry unevenly. Portions of a yard may:
• Stay too wet
• Be too compacted
• Hold salt runoff
• Lack nutrients
• Contain buried debris or construction waste

Trees with imbalanced soil conditions frequently decline on one side first.

7. Competition or Shading

If another tree, building, or structure shades one side, the tree may:
• Reduce growth on the shaded side
• Produce longer, weaker branches
• Drop more needles or leaves on the crowded side

This is common in tight Calgary yards.

8. Lightning or Storm Damage

Localized storm injury can kill only part of the tree, especially:
• Branch tearing
• Leader damage
• Wind strain
• Ice loading

Damage may not appear until the following growing season.

When One-Sided Decline Is Serious

A tree may be in significant danger if:
• The declining side spreads year after year
• A major structural branch has died
• Bark is sloughing or cracking
• Fungal growth appears on the dying side
• The tree leans toward targets
• The trunk shows seams or splitting
• The root flare is soft or decaying

Localized decline often precedes larger structural failure.

How Arborists Diagnose the Problem

A professional assessment includes:
• Examining roots and soil conditions
• Checking for fungal infection or decay
• Inspecting bark wounds and trunk damage
• Testing branch viability
• Identifying pests or disease
• Assessing canopy balance and wind exposure
• Reviewing watering practices

Because causes vary widely, correct diagnosis is essential.

Can a Tree Recover?

Recovery is possible when:
• Only small branches are affected
• Root damage is limited
• The issue is seasonal (sunscald, winter burn)
• Pests are caught early
• Soil conditions can be corrected

However, if major roots have died or trunk decay is present, decline may continue despite efforts.

What Homeowners Should Do Immediately

• Avoid pruning until assessed—incorrect cuts worsen decline
• Check soil moisture deeply
• Avoid digging near the base
• Look for signs of pests or disease
• Photograph changes for monitoring
• Call an ISA Certified Arborist

Partial decline is often an early warning sign of larger issues.

Why Choose Calgary Tree Care

Our ISA Certified and TRAQ Qualified Arborists bring over 15 years of experience diagnosing one-sided decline in Calgary’s challenging climate. We provide:
• Tree health evaluations
• Root and soil assessments
• Pest and disease diagnosis
• Structural pruning
• Evidence-based recovery plans
• Honest guidance on prognosis

We help homeowners determine the exact cause and the safest path forward.

Schedule a Tree Health Assessment

If one side of your tree is dying, don’t wait for the problem to spread.
Contact Calgary Tree Care for a professional assessment and targeted recovery plan.