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Protecting Our Waters -- Street Trees

Street Tree Planting Schedule | Tree Boxes
Preservation of Existing Trees
| Costs | Street Trees Regulations

Use of street trees is an important tool in an integrated stormwater management plan that can be applied to both existing and newly developing areas. It’s helpful for government officials to be aware of the many benefits trees contribute to the environment and the bottom line of the community's budget. However, fallen tree leaves contain phosphorus. If they are not picked up, the phosphorus can accumulate in local waterways. Municipalities would need to consider a leaf collection program. While there are programs and standards to reference, it is important to refer to experienced landscape architects to determine the appropriate planting strategy to implement.

As communities develop guidelines for stormwater best management practices, use of street trees should be incorporated. Key elements of ordinances include spacing guidelines for trees along new or reconstructed roads and preventing removal of existing trees along a road corridor. Boulevard sections, if used, should be sunken. Curbs and gutters should be eliminated so grass and trees can be planted.

Prior to settlement, the lands within the Milwaukee River Basin were primarily a southern mesic forest. The predominant trees in mesic forests were sugar maple, basswood, beech, slippery elm, red oak, and ironwood. Image of a row of trees next to a paved city street.The canopy from these trees prevented much of the rain from falling to the ground and therefore little surface runoff was generated. As settlement occurred, large areas of the forest were cleared for agriculture. (1) Continued settlement converted much of the land from agricultural to the urban land uses we have today.

Because streets constitute such a large portion of the impervious cover in a typical urban area, planting trees along streets to provide a canopy becomes an important part of managing urban runoff. Trees can be planted in the terrace area between the street and sidewalk or in certain boulevard sections. Trees reduce the amount of runoff by intercepting rain in their canopies and allowing it to evaporate. The United States Forest Service reported in a 1991 study that tree canopies in Chicago reduced urban storm water runoff 4 to 8 percent. (2)

A 1991 study by the United States Forest Service reported that tree canopies reduced urban storm water runoff by 4 to 8 percent.In addition to capturing rain and reducing the amount of runoff, street trees also provide shade and reduce surface and runoff temperatures.

Another study done in Modesto, California showed peak summer air temperatures could be reduced by 0.2 F for each percentage increase in canopy cover. (3)

Street Tree Planting Schedule -- Back to Top
A street tree-planting schedule outlining acceptable species and minimum spacing requirements can be adopted for both existing and newly developing urban areas. To provide a continuous canopy, shade trees are typically spaced between 25 to 35 feet apart along both sides of the street in an alternating pattern.

Actual spacing is dependent on the type of trees selected and their mature size. A local forester, arborist, or landscape architect can provide an appropriate tree-planting schedule that considers local climate and soil type.

Trees should also be planted in boulevard sections when possible. Besides the aesthetic value, it has been shown that properties on tree-lined streets have a higher value than those without. (3)

Tree Boxes -- Back to Top
Tree boxes are square, concrete boxes designed to hold a tree and fit into a curb. These boxes can collect frequent runoff from ¼ acre of pavement, allowing the tree roots to absorb the runoff and some of the pollutants accumulated on the pavement. (4) This technique may not be feasible in areas where extremely high pollutant loads are expected or where salt is used for de-icing streets in the winter months. Road salt and excessive pollutants can cause damage to the trees.

Image of a road in a residential district lined with trees.Preservation of Existing Trees -- Back to Top
Many mature, existing trees are removed during clearing operations for road construction. Efforts are occasionally made to preserve large trees where they don’t adversely affect construction activities or the traveling public.

However, smaller trees are often removed. This becomes a problem when road builders restore the roadway and replace these smaller though established trees with very young ones that require significant maintenance.

Besides environmental costs, this process of removing trees results in increased project costs due to excess clearing, purchase and maintenance of new trees. It may be necessary to allow narrower road widths and tighter turning radii, where applicable, to preserve existing trees near the roadway. However, narrower roadways will also save on project costs and reduce impervious cover and runoff (also see Streets and Roads).

Costs -- Back to Top
Municipalities can offset the costs of planting street trees by asking landowners for participation in a municipal-directed planting program. City parks department or forester can give residents guidance on the types of trees to plant. The resident installs and maintains the tree, and the municipality may offer a one-time tax credit to partially reimburse the taxpayer for a portion of the tree cost.

The municipality may also develop an adopt-a-tree program where municipalities purchase trees and taxpayers or civic groups are responsible for installation and maintenance. Local conservation or natural societies may also be solicited to make donations toward planting and maintenance of street trees.

Street Trees Regulations -- Back to Top

The WDNR has no regulations for Street Trees, and no state minimums.

State Statutes

(5) Mutilation of trees. It shall be unlawful for any person to injure, mutilate, cut down or destroy any shade tree growing on or within any street or highway in any incorporated village in this state, unless express permission so to do be first granted by the board of trustees of such village.

Source for text in oval:
McPherson, Gregory; Nowak, David; Rowntree, Rowan. “Chicago’s Urban Forest Ecosystem: Results of the Chicago Urban Forest Climate Project.” U.S. Department of Agriculture, Forest Service 1994.

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The Milwaukee River Basin Partnership is a voluntary coalition of businesses, non-profit groups, public agencies, educational institutions, organizations, and individuals committed to restoring and sustaining the ecosystem of the Milwaukee River Basin while ensuring its economic viability. To learn more visit,
Photos by Kim Sebastian, Wisconsin DNR, and Angie Tornes, National Park Service

This page was created on March 26, 2003.
This page was last updated on August 26, 2003.