Problematic Tree Species
There are many different tree species both exotic and native which would make wonderful additions to our urban forest, however there are a few which can prove problematic. There are two areas in which urban trees can cause unwanted costs and nuisance. Some trees can cause damage to water related utilities and in particular sewer systems. Silver Maple, Willows, Cottonwood and Box Elder are four trees which should never be planted in close proximity to water pipes or sewer systems. Their root systems actively seek out water sources and readily cause blockages in the water and sewer flow. This can prove to be very costly to both municipality and private owner when repairs need to be made. Secondly there are a few species such as Silver Maple, Willows, Aspens and Cottonwood that cause damage of a different kind. The rapid growth and structural nature of these species can lead to increased risk of limb breakage and debris. Because of there fast growing nature their structure is not as strong as many of the slower growing species. After a windy day or storm it is not uncommon to find many branches and even limbs below theses trees. This can cause damage to property and can prove dangerous to pedestrians. Although all these species have major problems and indeed become dangerous as they age, some, especially Silver maples, are still commonly planted by property owners who are perhaps unaware of the long term hazards. All of the previously mentioned species should not be planted in an urban environment. In many municipalities there are specific ordinances banning the planting of these species. Even if your community does not have specific ordinances prohibiting these species it would be advised not to plant them if not for the future costs they may entail but for the safety of property and pedestrians.
Another interesting problem has emerged in recent years with the increased popularity of flowering pears. These have become very popular due to the attractive flowers, dark green glossy leaves and often spectacular deep red long lasting fall color. The latter characteristic can create major problems as flowering pears may still have extreme leaf cover into November when early snow can fall. Some varieties of flowering pear have weak branch structure that may cause the tree to literally disintegrate under the snow load. Especially unfortunate is the fact that this won't usually happen until the tree has just reached a nice shape. If you really want to plant a flowering pear investigate very carefully the structural characteristics of the different varieties and choose one that is considerably less susceptible to snow load damage.