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Published on: Apr. 17, 2012

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Trees can be stressed by city life just like us. Cars, pollution, home improvement projects that take too long, summer heat and other factors cause urban trees to live significantly shorter lives than trees growing in natural settings.

Urban tree stress affects trees in your community parking lots, streets, parks, your home and anywhere city conditions cause less than desirable factors for tree health and safety.

Unlike an insect infestation or vascular disease that can be managed with a single treatment option, urban tree stress almost always requires a comprehensive approach.

Knowing what to look for, and the right questions to ask, will help you gather the information that a Department of Conservation expert or your local private arborist needs to understand and help your tree.

How Stress Hurts Trees

Trees, like all living things, have adapted to thrive in certain conditions. They prefer a specific soil type, nutrients, space, moisture, temperature, and associated soil food web to reach their full potential. When a tree is taken from an environment to which it has adapted and is placed in a sidewalk tree well, for example, one or more of these needs is reduced or lost. This places stress on the tree and, subsequently, the tree will not be able to thrive. Stressed trees become more susceptible to common problems such as fungus, insects and diseases. Tree pests that are minor issues in the woods become major issues in urban trees.

Many Missouri trees can be used in urban environments when the right tree is put in the right place and is protected from avoidable health problems. Knowing what trees need, and the possible stressors for those trees, will help identify future problems and treatments.

Urban tree stress is usually the result of a combination of factors and each species of tree varies in its inherent ability to resist these factors.

Trees such as linden, elm and some oaks are well known for their hardiness in urban landscapes because they are able to thrive in difficult growing situations. The factors that create these difficult growing situations include competition with turf grass, compaction, nutrient-poor soils, under- and over-watering, temperatures too hot or too cold, pollution, improper planting, construction damage and heat-island effects. Age also plays a contributing role in the susceptibility to stress; newly planted trees, as well as older, mature trees, are most likely to be negatively affected. Root loss from construction damage such as grade changes, root cutting, or even driving over the roots, is a significant source of stress for trees of all sizes and ages. Reflected heat from nearby buildings, asphalt and concrete will make a tree and soil hotter and drier. Mulch volcanoes, the practice of mounding excess mulch against a tree trunk, encourage pests and fungus. The more of these factors a tree has to overcome, the more difficult it is for that tree to survive, even for the hardiest of species.

Diagnosing Your Trees

Symptoms of urban tree stress may differ by species, location, age and source of the stress, but there are many common factors. Look for stunted growth, excess stem sprouting, wilted and scorched leaves, and chlorosis (yellowing leaves due to nutrient problems). Other visual indicators may include bark cracks, cankers, decay and the sudden or increased presence of insect pests. A dramatic increase in fruit and seed production is a signal that a tree is under stress, as trees in decline often increase seeding as a final effort before they die. Harder-to-see symptoms include construction damage and infection by root-rot diseases. These may be identified by certain fungus growing in your yard.

Be aware that many of these symptoms may not occur until several years after the cause. The healthier a tree is, the more capable it is to fight off problems over time, but delayed reactions to minor and major problems are normal. The key is to assess not only the tree, but also the area around the tree and its history, such as when herbicides were applied on the turf, a water line was fixed or the last time it rained.

Caring For Your Trees

When it comes to managing urban tree stress, preventing problems is far easier and cheaper than curing them. Urban tree stress can be avoided by the addition of mulch, removing turf under trees, increasing soil aeration and nutrient availability, or reducing competition. The closer you can recreate natural conditions for an urban tree, the better chance it has to thrive. For example, a willow or cypress tree needs to be placed in a wet site, while a pin oak or pine needs acidic soils.

The cause of the stress and subsequent decline needs to be identified before management begins. If a tree is treated for boring insects when the real problem is drought, we will only temporarily fix the symptom but not provide a solution. Fertilizers added during drought or after construction damage are common, but the fix is only temporary and may only create other problems. Once the problem is identified, a plan should be implemented to address both the symptoms and the primary problem.

What You Can Do

Watch for small changes in the appearance and growth of your trees, these may be early warnings. Take pictures so you have something to compare to later.

Lots of trees can recover from minor stress if provided a little extra water. Infrequent, slow and deep watering simulates natural rainfall, giving the tree a nice big drink. Mulch applied 2–4" deep, over the largest area possible, is similar to the natural leaf litter you see in the woods. This keeps soil cool, adds nutrients and keeps the mower from hitting the trunk.

If considering a remodeling project, don’t cut roots because the guy with a trencher or backhoe says it is OK. A small delay until fall or winter can reduce problems. Sometimes patience, and considering the basics, such as water and mulch, are your best choices.

What a Professional Can Do

A professional arborist is the best choice when you are worried about the health of your tree. Arborists can assess your trees with the knowledge of the whole region and provide the best information and recommendations. They may use compressed air excavation to loosen compacted soil or to find roots before a construction project. They may also apply soil, nutrients, growth regulators or other chemicals for specific problems. Arborists can make protection plans to work within your construction project needs. Those site and tree-specific options make hiring a certified arborist a wise choice. Visit the International Society of Arboriculture’s website at isa-arbor.com and look for “verify an arborist” to find a certified arborist in your area.

It Works!

Keeping an eye on your trees will maximize their health, appearance and services provided to you. A healthy tree is safer, makes more shade, grows faster and can tolerate heat waves, high wind, droughts and other urban stress.

Trees at your home and in the community provide real economic value by shading your house, protecting or adding value to property, providing pedestrians safe areas from traffic and cleaning the water before it reaches our streams and lakes all over Missouri. Visit itreetools.org/design to find out what trees do for you.

Many urban tree stressors can be avoided by placing the right tree in the right place for the right reasons. Be nice to your trees and they will be nice to you. Contact your local MDC urban forester or visit mdc.mo.gov/node/3797 for more information.

Some Factors That Contribute to Urban Tree Stress

  • Drought
  • Reflected heat
  • Soil compaction
  • Freezing / warming fluctuations
  • Defoliation
  • Nutrient deficiencies
  • Chemical injury
  • Over-watering
  • Mechanical damage
  • Transplant shock
  • Improper planting depth
  • Lack of root space
  • Competing vegetation
  • Improper pruning

Typical Symptoms of Urban Tree Stress

  • Excess sprouts
  • Leaf scorch
  • Wilted leaves
  • Dead parts
  • Stunted growth
  • Increased fruit production
  • Chlorosis
  • Girdling roots
  • Early fall color change
  • Early leaf drop

What is Bugging Your Tree?

Urban stress can lead to insects. Sometimes the insects are easy to see and sometimes all you see is the damage they cause. For a faster and more accurate diagnosis, collect the following information to share with your arborist.

  • Do you see insects? What do they look like? What color are they? How big? Are they flying or walking? Do you see them in a web?
  • Are leaves chewed or do they look like something poked a hole and sucked the juice out? Does it look like something tunneled inside the leaf?
  • Is the leaf dried out? Are the edges dry or the whole leaf?
  • Is the leaf turning yellow from the veins outward or from the edges in?
  • Are there weird bumps or warty-looking things on a twig or leaf?
  • Are the leaves or area under the tree sticky?
  • Take a picture of the problem from close up and another showing the tree and area surrounding it.

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