Maintaining Roadway Infrastructure and Parkway Trees
Public Works aims to maintain healthy parkway trees along with providing safe travel for motorists and cyclists on County roadways and safe access for pedestrians and individuals with disabilities under the Americans with Disabilities Act on County sidewalks. To accomplish this, the street pavement and concrete curb, gutter, and sidewalk are routinely maintained and periodically replaced. As parkway trees in our urban forest age, their canopy and roots grow. Often the parkway tree roots grow beyond the narrow green space between the sidewalk and the curb and in the process, displace the adjacent infrastructure.
Why are parkway trees root pruned?
Parkway trees are sometimes root pruned in order to accommodate an adjacent infrastructure repair. Before a tree is root pruned, it is evaluated by the Urban Forestry Unit to determine whether the tree can be safely root pruned per ISA standards to allow the replacement of the adjacent sidewalk and/or curb and gutter. If the tree cannot be safely root pruned, it may be removed and in most cases, replaced.
Why can't all parkway trees be safely root pruned?
Tree roots may grow two to three times beyond the drip line of the tree canopy and most exist in the top 18” of soil. There are many factors that affect a tree’s tolerance for root pruning including the following:
Sustainable community solutions
Because the County has approximately 160,000 trees, over 2,600 miles of sidewalk, nearly 3,400 miles of curb and gutter, and over 9,500 lane miles of roadway to maintain, our choices for how to maintain the trees, the street and parkway need to be economically sustainable.
Parkway tree species selection
When parkway trees are replaced, Public Works makes every effort to select tree species that are both complimentary to the other parkway trees in the neighborhood and appropriately sized at maturity for the parkway. A list of recommended parkway tree species along with tree photos can be found on our website on the Tree Planting page.
Parkway trees are not the only trees that sometimes damage public infrastructure. At times, roots from private trees extend under and displace sidewalks. When this occurs, Public Works will notify the underlying property owner and provide them with the opportunity to root prune their tree so that Public Works can replace the sidewalk without damaging the private tree. If the tree roots are not pruned, Public Works may opt to replace the concrete sidewalk with asphalt in order to better preserve an accessible sidewalk surface.