by Valerie Rodrigez-Lewis

Tree grates are intended to allow air and moisture into the soil while creating more pedestrian, or hard surface area. These grates are designed to be both pro-people and pro-tree. However, there is an ongoing debate over their benefits to the tree. Opponents argue that they stunt root growth and actually cause compaction because of their weight. Proponents argue that any harm to trees is caused by improper support, size, and maintenance. This debate will most likely go on for a long while. In the meantime, both sides of the debate agree that careful site-by-site considerations are necessary to ensure a healthy tree.

On sidewalks, tree grates are definitely a decorative feature that can add a clean urban look, but more importantly, they are a safety feature protecting pedestrians from the hazards of an open tree well that may have a significant grade change. The increased surface area comes in handy on sidewalks with already limited space. This safe pedestrian area is a tree grate's biggest selling point. Sidewalk space is so critical that the ADA has determined a minimum width of 3 feet.

Opponents believe that tree grates, which are normally 5 to 6 feet, should not be used on large shade trees because they tend to concentrate the best conditions for root growth in a narrow space around the trunk. However, manufacturers like Ironsmith make tree grates up to 12 feet in diameter to handle larger trees. Manufacturers do concede that use of grates requires a careful site-by-site and tree-by-tree analysis and that larger trees will require larger grates. It is assumed that the extra expense deters LA's and their clients from using appropriate sized grates.

Opponents claim that root growth is also hindered because support for the tree grate creates a ring of compaction. However, manufacturers of tree grates note that damage is most likely to occur if the grate is not properly installed and that the grate itself is designed to prevent compaction from foot traffic. Manufacturer's feel these claims of compaction are unsound because the tree grate itself is lighter than the concrete sidewalk and that support for the grate is not that much heavier.

Other things to consider when deciding to specify a tree grate include the necessity of access to the root zone after the tree has been installed and the possible need to expand the tree opening and the maintenance involved.

The look of tree grates as well as the benefits of a larger and safer walking space may preclude these other concerns if people are the main concern. Though, if trees were really the main priority, designers should probably do without sidewalks altogether.