When Trees and Sidewalks Clash: Understanding a Common Urban Conflict

Photo: Ildar Sagdejev

By Susan Mates

Cracked and lifted sidewalks are one of the most common complaints about mature

street trees. But the roots causing the damage are simply trying to survive. Most

grow in the top 12–24 inches of soil, where oxygen and water are available. In

compacted urban soils—especially along streets—roots are pushed even closer to

the surface. As they expand, they can lift or crack the pavement above.

Urban trees are essential infrastructure. They shade streets, cool neighborhoods,

clean air and water, store carbon, and support wildlife. The challenge is finding the

right balance between two public goods: healthy trees and safe sidewalks.

Why Tree Roots Lift Sidewalks

The real struggle happens underground. Roots need space, water, oxygen, and

nutrients—resources often limited in urban settings. So they grow where

conditions are best: near the surface, often just beneath pavement. Over time, as

roots thicken, they press against sidewalks and curbs, causing them to shift and

crack. Understanding this process is the first step toward smarter, longer-lasting

solutions.

Photo: Ildar Sagdejev

A Costly Urban Issue

Sidewalk damage from tree roots is expensive—and most cities pay after the fact.

That raises a key question: invest now to prevent problems, or keep paying more

later?

Repairs add up fast—grinding raised edges, patching cracks, replacing slabs. In a

litigious climate, the risk of lawsuits can skew decisions toward smaller trees,

frequent replacements, or even removing street trees altogether.

Tree removal isn’t cheap either. Establishing a new tree is most expensive in its

early years, and replacing a mature tree means losing the cost savings of decades of

benefits—shade, cooling, stormwater capture, and more.

Prevention is often cheaper than repair, especially with many promising ways to

reduce tree-sidewalk conflicts. And preserving mature trees can be a big savings

when their benefits are included in the cost equation.

What Researchers Still Hope to Learn

Although cities have decades of experience dealing with damaged sidewalks,

several knowledge gaps remain. Future research is needed to better understand how

different tree species and root architectures interact with pavement, and how

management practices like pruning and irrigation influence root growth. Other

questions include which sidewalk construction designs are best for tree roots, and

how to allocate funds effectively among repair, prevention, mitigation, and legal

costs.

Finding the Balance

Urban trees are essential. They cool neighborhoods, filter air pollution, store

carbon, and make streets more inviting places to walk. Sidewalk damage from

roots is a real challenge. But it’s also a sign that our living urban forest is doing

what it was evolved to do—grow. With thoughtful planning, better soils, and

smarter design, we can find ways for healthy trees and stable sidewalks to coexist.

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Resources:

● Trees and Sidewalks - Healthy Roots, Healthy Tree, Carrie Black,

Portlnd.gov, March 31, 2021.

● A Review of Tree Root Conflict With Sidewalks, Curbs and Roads, Randrup,

McPherson and Costello, Urban Ecosystems, 5: 209–225, 2001, April 26,

2000

● Street Trees and Sidewalks, Feet First Policy