|Photo Credit: Raina Sheridan, Southern Regional Extension Forestry|
To ensure a tree will grow and develop to maturity, it is essential to evaluate the environmental conditions of a site.
Consider the amount of sunlight, shade, and artificial light at the site, including the duration and directness of sunlight. How often is the tree in full sunlight or shade? Are there buildings or other trees shading the site? Are there artificial lights shining on the tree all night? Is there reflective light from buildings, streets and other structures? Light patterns can even change the dormancy and growth patterns of a tree. Visiting the site at different times of the day and season will help in determining the light patterns and in selecting a species appropriate to those conditions.
It is important to know if a species can survive the temperature extremes at the planting site. The average minimum temperature can be determined from hardiness zone maps. Urban areas are usually warmer than rural ones because of the "heat island" effect, but site-specific factors can cause even greater extremes. For example, trees planted next to a black asphalt road will likely experience higher temperatures and will probably need more water than those planted in the middle of a park or yard. Some sites are subject to early and late frost, such as ridgetops, large open spaces, low areas, and frost pockets.
Precipitation patterns directly influence site conditions. How much rainfall does the site typically receive? When are the dry months? Is there a history of long periods of rain that can waterlog the soil? Snow and ice increases the weight on the branches and may break branches and cause other injuries. Select a species adapted to the precipitation patterns at the site.
Strong winds may blow down trees and snap trunks and limbs. Constant winds increase the tree's need for water because of increased transpiration. Buildings in downtown areas can create a wind-tunnel effect and increase the wind speed in those locations. Are wind storms, tornadoes, or hurricanes common in the area? Sites exposed to strong winds should have adequate soil volume for good root development, and the tree species should have a structure and branch attachment that can tolerate windy conditions.
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By: Ed Macie, Regional Urban Forester, US Forest Service Southern Region