Environmental Factors to Consider

James R. Fazio Editor

When selecting a tree, your first consideration must be what the tree needs. In other words, what environmental factors limit the ability of a particular species to thrive in an area?


Varying temperature ranges limit the geographic diversity of many species of trees. Low temperatures, especially if they come suddenly, can freeze and kill the living cells in trees not suited to colder climates. The same reaction can occur in many species that are not accustomed to high temperatures and drought conditions. Select a species suitable to the zone where you live. Remember, elevation and exposure differences (the direction of the slope) within each zone also have an effect. North slopes, windy sites and higher elevations can make a site equivalent to one or two hardiness zones lower.


Each species can tolerate wet or dry growing conditions to a different degree. Special attention must be given to your selection if the site can flood, is subject to very dry conditions, or is continually exposed to the drying effect of wind. Watering, of course, can modify a dry site, but even when you irrigate it is important to know the optimal soil moisture requirements for your species. Light, sandy soils could be watered more frequently. Watering every day or every other day is way too much.


Shade tolerance is the term foresters use to rate the light requirements of each species. Don’t make the mistake of planting your tree where it is mismatched with its need for light.


Every locality has its problems with a particular insect or disease. The best way to avoid trouble is to avoid species that host these pests. In some cases, it is possible to buy varieties that have been bred for resistance to a disease.


Soil factors are probably the most overlooked when selecting a tree. Soil depth, structure and pH, in addition to soil moisture, can make the difference between success or failure after planting. Species that need light, sandy soil should not be planted in rocky or clay-type soils. Also, each tree species has a tolerance range related to acidity and alkalinity just as it does for shade. This requirement should be matched with the soil where you plan to plant. Soils are often disturbed in urban areas and trees which would typically do well may struggle due to poor soil structure. Compaction of the soil due to heavy pedestrian or vehicle use often reduces a tree’s growth and size potential.

Air Pollution

Unfortunately, the ability of a species to tolerate air pollution is becoming more important. Chemicals in the air vary with localities, and in some cases the accumulative effects of pollution are just beginning to show up. The best course of action is to ask a local professional if there are problems in your town and, if so, what species are affected. Similarly, salt spray from either the ocean or street de-icing can be a problem locally and some species are more sensitive to it than others. Where these are problems, ask an arborist, nursery professional, urban forester, or AgriLife Extension agent about which trees to avoid.


In summary, it is important to analyze the various environmental factors in your area before selecting a tree. Temperature, moisture, light, pests, soil conditions, and air pollution will all affect your planting success.


Tree City USA Bulletin for the Friends of Tree City USA

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