Why do people put metal bands around trees?

Metal bands around trees, often referred to as tree guards or tree grates, serve an important purpose in urban environments. As cities expand, more and more trees end up growing in paved areas surrounded by concrete and asphalt. While trees greatly enhance the livability and aesthetic appeal of urban spaces, they also face challenges in these hardscape settings.

Protecting Tree Trunks

One of the primary reasons tree guards are used is to protect young trees from damage. Tree bark is easily injured by impacts from vehicles, bicycles, pedestrians, and lawn care equipment like weed whackers. These injuries leave trees vulnerable to insects and diseases. Over time, repeated impacts can severely damage or even kill a tree.

Tree guards prevent direct contact with tree trunks, shielding them from incidental bumps and scrapes. They create a barrier that reminds people to be more careful around the tree. Tree guards are especially important along high traffic areas like sidewalks, plazas, parking lots, and streets.

Preventing Soil Compaction

Soil compaction is another threat to urban trees. Foot traffic from people walking over the root area compresses soil, reducing the tiny air pockets that roots need for gas exchange. Without proper aeration, roots cannot take up nutrients and oxygen. Severe soil compaction can asphyxiate and kill trees.

Tree guards keep pedestrians from walking directly over the root zone, diverting foot traffic around the perimeter instead. This protects the soil structure and porosity. Tree guards are particularly beneficial whenever foot traffic is channeled along narrow spaces like planting strips between roads and sidewalks.

Defining Spaces

Tree guards also serve as visual design elements that define spaces in the urban landscape. The circular shapes help distinguish between different zones like pedestrian walkways, parking areas, seating plazas, etc. The uniformity of tree guards along a block or corridor creates visual cohesion.

In plazas or seating areas, guards around individual trees create protective islands for the trees within the surrounding paved space. This delineates the planting zones to encourage people to walk around rather than through them, keeping foot traffic dispersed.

Benefits to Trees

When properly installed and maintained, tree guards provide the following key benefits:

• Protect tree trunks from scrapes and bumps
• Shield bark from string trimmers and lawn mowers
• Prevent soil compaction around roots
• Reduce injuries that lead to insect and disease problems
• Define planting areas and influence pedestrian flow
• Visually delineate different use zones

Materials Used

Tree guards come in a variety of styles and materials:

• Plastic or rubber guards – Flexible rounded pipes that wrap directly around trunks. Often used in temporary installations.
• Metal guards – Decorative iron, steel or aluminum guards with vertical bars. Allow some air and light into interior.
• Concrete curbs – Solid masonry curbs poured around perimeter of planting area.
• Wood guards – Made of thick timber, slightly angled away from tree. Softer appearance.

Metal is one of the most common and durable materials used. Iron and steel tree grates allow maximum water, air and light penetration. The vertical bars flex if bumped, without harming trees. Metal finishes like powdercoating, galvanization, or paint prevent rusting and enhance aesthetic appeal.

Ideal Design Features

Well-designed tree guards have some or all of these features:

• At least 2 feet away from the tree trunk
• Enough interior space for growth over time
• 4-5 feet diameter minimum
• Gently rounded or smooth edges
• Durable, long-lasting materials
• Vertical or angled bars spaced 2-4 inches apart
• Short enough to allow lawn care yet discourage walking over root zone
• Visually appealing style that fits surroundings

Proper Installation

Tree guards only work when properly installed:

• Allow space between guard and trunk
• Center guards over root ball
• Set vertical guards 1-3 inches into the ground for stability
• Angle guards slightly away from the tree
• Secure guards in place with anchored posts or stakes
• Mulch around exterior perimeter to discourage weeds

Ongoing Maintenance Needs

Tree guards require periodic inspection and maintenance:

• Check for insect or disease problems inside guards
• Adjust to accommodate trunk growth
• Keep surrounding mulch tidy and replenished
• Remove trash or debris around guards
• Check for soil erosion under edges
• Inspect condition and recoat/repaint as needed

As trees grow, grates will need periodic expansion or eventual removal. Allow trunk diameter clearance of at least 2 inches for continued healthy growth.

Using Guards Effectively

Tree guards effectively protect city trees in paved environments, but only if used properly. Some key points include:

• Select appropriate guard size, spacing and materials for the species and setting
• Install carefully to avoid damage and future conflicts with roots or branches
• Maintain guards over time for continued benefits
• Adapt or remove guards as trees grow to avoid girdling
• Use guards selectively where threats exist rather than routinely everywhere

With proper selection, installation and care, tree guards enable trees and people to thrive together in urban environments. They help make trees a safer, more viable part of the infrastructure in cities.

When Guards Are Not Recommended

While tree guards are very useful in many urban locations, they are not recommended in all cases. Situations where tree guards may do more harm than good include:

• Around trees in groves or wooded areas away from traffic
• Around mature trees that do not need protection
• Overuse where trees are not threatened
• Improperly sized or installed guards that restrict growth
• Areas where guards would impede mowing or maintenance
• Around trees prone to insect/disease problems requiring more air circulation

It is better to avoid using guards in these situations. The goal is to protect trees, not create new problems.

Careless Use Can Damage Trees

When tree guards are improperly used, they can actually endanger trees. Potential risks include:

• Guards placed too close to trunks may girdle trees as they grow
• Guards that are too small or inflexible can constrict expanding trunks
• Guards that are too large waste space and resources
• Guards that are left on too long will require expansion or removal

Ongoing inspection and maintenance is key to avoiding these negative impacts over time.

Alternatives to Tree Guards

In situations where tree guards are not the best option, some possible alternatives include:

• Planters – Provide a buffer zone around trees with more room
• Curbs – Help define planting areas and discourage soil compaction
• Bollards – Physically block direct access to prevent damage
• Diverter strips – Channel foot traffic away from tree bases
• Signage – Educate people to be careful around tree roots
• Fencing – Keep people and equipment away from tree areas

Careful site planning, protective barriers, and public education help create safer growing conditions for urban trees without using tree guards.

Key Takeaways

Here are some key points to remember about the use of tree guards:

• Help protect tree bark from scrapes and impacts
• Shield trunks and roots from soil compaction
• Visually define planting areas in urban environments
• Require proper installation and ongoing maintenance
• Should be adapted or removed as trees grow over time
• May not be needed or appropriate in all cases
• Can damage trees if improperly installed or maintained

When used selectively in the right conditions, tree guards are an invaluable tool for growing healthy trees in paved urban areas. Like any tree care practice, guards require informed use and stewardship to yield real benefits.

Conclusion

Tree guards play an important role in urban forestry. They help young trees become established in stressful paved environments. Without protection, many trees would suffer significant damage or fail to thrive. Thoughtful use of guards helps expand tree canopy in cities, providing critical environmental, economic and social benefits.

However, tree guards must be used judiciously. They are just one tool among many for growing healthy urban forests. With careful selection, proper installation and ongoing maintenance, tree guards help trees and people coexist in close proximity for decades to come.