Tree Diversity

Choosing a tree should involve more than just picking one that you like the looks of and is suitable for you planting space. To improve the quality of urban forests as a whole your choices should also consider what else has been planted in the area. The over planting of a small number if of tree species can be seen throughout virtually all urban areas. In some cases more than fifty percent of the urban trees in an area can be of a single species (an interesting exception to this trend is Ithaca NY which has over 100 kinds of street trees). Why is it unfavorable to plant the same species of trees throughout the urban environment. The problem here is the lack of diversity. In any forest ecosystem diversity plays a major role in long term stability. An urban forest ecosystem is no different. Overuse of a single type of tree greatly increases the vulnerability of the tree itself and the urban forest as a whole to pests and disease. With low tree diversity it only takes one parasite or disease that affects a particular species to wipe out the many of the trees in that area. One only has to look to our past to when Dutch elm disease exploded in North America during 1930 and quickly devastated native elm populations. The spread of this disease was greatly amplified due to the abundance of elms in many urban environments where they had been widely planted for their beautiful shape and wonderful shade. Older residents may remember Leroy St. in Binghamton for is elms. Within a few decades virtually all of the forested urban areas were left with out any trees due to the extensive elm die off. The importance of diversity in urban trees should have been acknowledged from this point forward but unfortunately many urban forests today are still mainly made up of one or a few tree species.

Today the most widely planted urban trees are maples, of which the Red and Norway maples are the most common. The overwhelming numbers of maples in our urban forests could be headed down the same road as the elms. Black spot or tar spot fungus of Norway maples is becoming prevalent in many areas and is quickly spread from tree to tree when in close proximity. This fungus attacks the maturing leaves of maples in spring and develops throughout the year into black spots on the mature leaves. Although this fungus is not lethal it can greatly diminish the aesthetic value of the infected tree. Dutch elm disease and black spot are just two examples of how decreased tree diversity can lead to the increased speed and severity of a disease or parasite.

Diversity and in turn stability of our urban forests can be achieved extremely easily. When choosing a tree species eliminate common and over planted species from you list of choices. For most urban areas in New York and the Northeast in general avoid maples as they are invariably the most over planted. However one should take into consideration their local areas as it could be different from the general urban trends. A tree species that is less common or even exotic can offer many benefits to our urban environment. Along with all the benefits that coincide with the increase in diversity that an uncommon or exotic tree species can have, these species can also add an increased aesthetic quality to the often monotonous plantings of many urban environments. An unusual tree species can become a focal point of a street and can encourage others to consider planting interesting species thus fueling diversity even more. Uncommon or exotic species should not be assumed to be more expensive or requiring increased maintenance. Many species require almost no care once established and are often comparable to many of the more common species. Often these species outlive their more common counterparts due to decreased death rates from communicable diseases and parasites which can plague other more common species in an urban environment.

If your community has a tree planting program, your choices may be limited depending on the awareness and creativity of the responsible government official. However, for a relatively modest investment one can buy a wide variety of suitable trees shown on this web site and either plant them yourself or have it done by a landscape contractor. Having the only Zelcova or Chinkapin oak in the neighborhood can be an interesting aspect of your property.

Last Updated: 2/25/15