Issue 9, June 17, 2011

My Tree is Stressed!

Stress is caused by a difference between what a plant requires from its environment, and what is available to it. Stress makes trees vulnerable to pests, such as borers, and pathogens, such as cankers. It is a factor in all but the most virulent conditions.

Plant diseases are best avoided. Careful plant selection can prevent problems that are difficult or impossible to remedy. This is especially true of trees. They are (potentially) large, long lived elements of the landscape. Each species has evolved to fit into a discrete environmental niche; your tree will reach its genetic potential only if it matches your site.

Will your selection have room to mature? Roots can spread through the top 30" of soil for twice the height of the tree; is there room underground? Is the soil compacted? Has the top soil been stripped? Some trees (notably those that inhabit floodplains) are more tolerant of disturbed urban soils than others. If your selection is pH sensitive (pin oak or sweet gum, for example), have the site tested. It is very hard to change the pH of highly buffered Illinois soils.

This photo shows the roots of an evergreen that was planted in a compacted site

Is the tree adapted to the volatile climate of the prairie state? This includes cold and heat tolerance, as well as the ability to endure sudden changes in temperature. Trees that evolved in maritime regions, such as Japanese maples, are often injured by sudden temperature fluctuations. How much sunlight does the site receive? Shade tolerant denizens of mature forests, such as sugar maples can find exposed sites stressful. Windy sites can cause winter desiccation in broadleaved evergreens , such as rhododendrons, or boxwoods. Their foliage loses water; their roots can't replace it if the soil is frozen. Many conifers, notably Colorado spruce, will die in dense shade. What other plants are present? Groups of plants are better able to withstand high winds and desiccating heat, but large established trees are aggressive competitors.

Firs receiving too much shade in an understory of pines (photo by Nancy Pataky).

Trees can endure, for a time, miserable growing conditions. They will cling to life on tiny parking lot islands, in tree coffins awash in exhaust fumes, on sun baked clay lots in raw subdivisions. They bring solace to human beings who are also trapped in stressful environments. But, the best tree for any site is one that belongs there and will grow and thrive in the conditions that are found there. (Jean A. Burridge, ISA Certified Arborist and Edited by Stephanie Porter)

Stephanie Porter

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