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