How Climate Change in Colorado Is Affecting the Urban Forest

Colorado’s climate has always been challenging for trees. High elevation, dry air, intense sunlight, and temperature swings make it a tough environment even in normal conditions. But over the last decade, our urban forests—from Fort Collins to Pueblo—have been experiencing stress beyond what many tree species were designed to handle.

As certified arborists, we’re seeing the impacts of climate change unfold in real time: unusual pest outbreaks, longer droughts, sudden cold snaps, and species decline. These changes don’t just affect forests in the mountains—they affect the trees in front yards, parks, streets, and patios across every city along the Front Range.

Understanding what’s happening helps homeowners make better decisions about planting, watering, and long-term care.

What’s Changing in Colorado’s Climate?

While climate change is a global issue, Colorado’s local climate patterns have shifted in specific ways that directly impact tree health:

1. Hotter, Longer Summers

Colorado is experiencing:

• Higher average summer temperatures
• More days above 90–100°F
• Longer periods without precipitation

Trees lose moisture quickly in these conditions, especially in shallow, compacted urban soils.

2. More Frequent Drought Cycles

Drought isn’t new to Colorado, but it’s becoming:

• More severe
• More frequent
• Longer-lasting

Even if a tree survives one drought, repeated cycles weaken its root system and make it more vulnerable to pests and disease.

3. Reduced Snowpack

Winter snowpack traditionally provided slow, steady moisture to the soil. With less snow and earlier melt:

• Roots enter spring dry
• Soil moisture disappears faster
• Winter watering becomes critical

This is a major reason we see winter desiccation in evergreens.

4. Sudden Temperature Swings

Colorado now sees dramatic shifts such as:

• 70°F one day, deep freeze the next
• Late fall warm spells followed by hard freezes
• Winter warm-ups triggering early bud growth

Trees do not adapt quickly to these swings. It leads to freeze damage, split bark, and dieback of new growth.

5. Milder Winters

Cold winters used to kill pests and regulate insect population cycles. With fewer extremely cold days:

• More pests survive winter
• New pests expand into the region
• Insects produce additional generations per year

This is one reason we’re seeing bark beetles, Japanese beetles, mites, and aphids stay active longer and at higher levels.

How Climate Change Affects Urban Trees

Urban trees face unique stress. They don’t grow in deep forest soils—they grow in compacted, disturbed ground surrounded by concrete, asphalt, and reflective surfaces. Climate change adds extra pressure.

Here’s what we’re seeing:

1. Higher Tree Mortality in Certain Species

Some species simply weren’t designed for Colorado’s extreme drought and heat cycles. In recent years, arborists have seen decline in:

• Blue spruce (especially outside native range)
• Aspen planted at lower elevations
• Birch
• Mountain ash
• Some ornamental plums and pears

These trees were already marginal in some parts of the Front Range; climate pressure pushes them beyond their limits.

2. Increased Pest and Disease Activity

Many pests thrive in stressed trees. We are seeing:

• Ips and spruce bark beetles hitting ornamental trees
• Japanese beetles expanding into new neighborhoods
• Aphid outbreaks lasting longer into fall
• Spider mites thriving in hot, dry summers
• Fire blight spreading rapidly in warm, wet springs
• Needle cast fungi appearing in irrigated, humid urban environments

Insects and diseases don’t create climate stress—they take advantage of it.

3. Root System Stress

When drought cycles repeat:

• Trees shed small feeder roots
• Root zone shrinks
• Water absorption drops significantly
• Soil compaction worsens the problem

Even if you water a stressed tree properly after a drought, its ability to take up that water may already be reduced.

4. Heat Island Effects

Urban areas absorb and radiate heat:

• Roads
• Driveways
• Buildings
• Rock landscapes

These surfaces raise temperatures around trees by several degrees compared to natural settings. This is especially hard on newly planted trees or moisture-sensitive species.

5. Unpredictable Growing Seasons

Warm weather in late winter can trigger early:

• Leaf-out
• Sap movement
• Bud expansion

Then a sudden freeze kills tender growth.
We’ve seen trees lose an entire season of branch tips in one spring freeze event.

What Homeowners Can Do to Help

The situation isn’t hopeless—far from it. With thoughtful care, trees can not only survive but thrive in a changing climate. The key is adaptation.

Here’s how homeowners can support resilient urban forests:

1. Choose the Right Trees

Plant species adapted to:

• Drought
• Heat
• High sunlight
• Local soil types

Some reliable choices for much of Colorado include:

• Hackberry
• Bur oak
• Chinkapin oak
• Honeylocust
• Kentucky coffeetree
• Some elm cultivars (DED-resistant)
• Native conifers adapted to region

Avoid species highly sensitive to heat, drought, or alkaline soil unless conditions are ideal.

2. Improve Soil Health

Healthy soil = healthy trees.

• Add compost when planting
• Use wood chip mulch
• Avoid compacting soil near trees
• Use mycorrhizal inoculants in disturbed soils
• Support soil biology rather than relying on fertilizer alone

Soil biology is the foundation of climate resilience.

3. Water Smarter

Watering practices matter more than ever.

• Deep, infrequent watering
• Water slowly over several hours
• Focus on the dripline/root zone—not the trunk
• Winter watering during dry spells

Many trees that die in summer actually started declining during a dry winter.

4. Reduce Other Stresses

Climate change is a stress multiplier. Reduce avoidable stress:

• Proper tree pruning (no topping)
• Protect roots from construction
• Avoid overfertilizing
• Prevent mower or string trimmer damage
• Avoid compacted rock-only landscapes around trees

A tree under multiple stresses is far more vulnerable.

5. Embrace Diversity

One lesson from past decades: planting only one type of tree sets up disaster. Elm monocultures led to Dutch Elm Disease wiping out neighborhoods in the 1960s–1980s.

Today, we need biodiversity:

• Many species
• Many genera
• Varied sizes and planting ages
• Native species mixed with adapted non-natives

A diverse urban forest is a resilient urban forest.

The Role of Homeowners

You are the caretaker of the urban forest. Trees on private property make up most of the canopy in Colorado cities—far more than municipal plantings alone. The decisions you make:

• What you plant
• How you water
• How you prune
• Whether you protect roots during landscaping

…will shape the health of our urban forest for the next 30–50 years.

Small decisions today have big impacts tomorrow.

Final Thoughts

Climate change is not a distant threat—it is already affecting trees living in our yards. But trees are also one of our best defenses against rising temperatures, stormwater runoff, poor air quality, and loss of biodiversity.

The goal is not to fear these changes, but to adapt with intention:

• Plant smart
• Improve soil
• Water wisely
• Monitor for stress
• Ask for help early

With the right approach, the urban forest in Colorado can continue to thrive—even in a changing climate.