Being a tree in an urban environment is no easy task. Threats to trees are present in every leafy neighborhood. Knowing what they are can help us make plans to avoid the loss of a once healthy tree.
A tree growing on an undisturbed, undeveloped lot can attract the attention of a would-be developer and go from a thriving and healthy state to one of broken branches and compacted roots from the construction.
A young sapling planted carelessly in your neighborhood park will struggle to survive without some maintenance from day one.
And beloved mature trees can be stricken with all types of disease and insect infestations that will quickly end a species with a history of long life.
Let’s explore the many factors that present threats to our urban canopy.
Understanding The Major Threats To Urban Trees
The planting of a new tree is an event steeped in excitement, hope and instant beauty. A young tree brings the promise of decades of future shade, stunning flowers, and welcome wildlife.
Unfortunately, there can be immediate threats to a young tree’s burgeoning life. Planting a new tree requires mindful consideration of numerous factors.
Tree placement will have long term consequences for your new tree. For example, planting a tree to screen an unsightly view without considering the overhead power lines can undermine your new tree’s potential.
Often a young tree can establish on an urban site with limited root space and in a small planting bed. However, urban street trees planted in small terraces between the sidewalk and street eventually grow to a size where the roots will fail to find enough resources to continue to flourish. And the tree’s stability will be compromised because of limited structural roots.
Urban trees can also begin to cause damage if the large, anchoring roots begin to shift hard surfaces like sidewalks or driveways.
When it comes to planting your young tree, getting it placed in the hole at the correct depth is the number one priority after you choose a proper location. When you plant a tree too deeply, it’s likely the tree will develop stem girdling roots. Instead of the roots growing out from the tree like spokes on a wheel, they will start to encircle the trunk, which chokes the trunk tissue and leads to a shorter life, dieback in the canopy branches, and lack of stability.
Construction and Compaction
Compaction is a threat that is extremely common in urban areas. A new driveway or patio placed in close proximity to a valuable shade tree often results in roots being cut and soil compacted to create the base for the new patio, pathway or driveway.
Urban soils already tend to be compacted from the lack of organic matter allowed to build in the soil from fall leaf litter or twig and branch decomposition in the soil. That beautiful putting green lawn is compacted from a summer of mowing and the occasional game of soccer.
Mulch and soil aeration are often the answers to improving soil organic matter and increasing the pore space so roots have space to breath and grow.
Photo by Wioletta Płonkowska on Unsplash
Road salt is another threat that slowly degrades a tree’s ability to thrive. Road salt sprayed from the road by passing vehicles not only damages branches, but can also build up in the soil and lead to the tree’s inability to absorb water and nutrients.
Physical threats to trees are the result of a tree’s inability to defend itself from human or animal attack. Young trees without proper bark protection can suffer rodent damage over the winter months.
Lawn mowers and string trimmers can mimic the hungry teeth of a rabbit by damaging the bark at the tree’s root flare.
Aggressive pruning can injure branches and cause wounds that provide an opening for pests and diseases to infiltrate.
Climatic factors play a large role in the health of our trees. Trees exposed to weather extremes in the form of drought, flooding and extreme heat are pushed to the limits of steadfastness.
When trees are under the pressure of unstable climatic conditions, they become stressed, which can expose them to secondary pressures of diseases and insect infestations.
Photo by Dainius N. on Unsplash
Insects and Disease
Threats from native and non-native insects are an increasing crisis to native trees and shrubs in our urban, rural and forested places.
For example, Emerald ash borer is one of the deadliest threats to urban ash trees across the country. Chemically treating trees against a fatal insect infestation is often the only approach to preserving a high value tree in your landscape.
Tree diseases can trigger a cascading spread of infection among similar species in an urban landscape. The fungal disease oak wilt has caused the death of countless healthy oak trees. If left untreated it can spread through grafted tree roots and kill adjacent oak trees of the same species.
Dutch elm disease was one of the earlier fungal diseases to completely reshape whole city treescapes. The loss of elm canopied streets changed the fabric of cities in the midwest that will unlikely be recreated in the future.
Threats from diseases keep urban foresters and arborists constantly fielding calls about the condition of once healthy backyard trees that are now succumbing to urban stressors and diseases.
Understanding threats to trees in our cities and towns is not meant to evoke feelings of doom and helplessness. Instead, we can make decisions that take a proactive approach to taking care of trees and reducing potential harms. Planning for the long term health of current and future trees and landscapes is the first step in ensuring a green leafy future.