Street Tree Survival
A street tree is located in the public right of way, by definition, and does not include trees planted in front yards or on private property. Too often large investments are made in the planting of street trees without follow up maintenance to the newly planted trees. Newly planted trees have the highest mortality rate. Trees provide net benefits worth 2 to 3 times the cost of planting and caring for them over a 30 year period.
Street trees substantially reduce energy use and provide air cleansing and pollution reduction for cities that is estimated to be worth millions of dollars each year. Street trees need the attention of a well-informed public, they need to be monitored on a regular basis and cared for in times of stress. Most people, however, do not realize that trees living in the urban environment need to be cared for. Along with that misunderstanding, there is the issue of whose responsibility it is to care for the trees. In addition to their neglect, there is vandalism and lack of respect for the tree.
Civic participation in street tree care depends on the support of the larger community, including the city government and private interests. Fortunately, organizations such as the Massachusetts Commmunity Forestry Council are working hard to educate and involve the Massachusetts residents in improving the quality of life and the environment through the planting and care of trees.
There are many reasons why the survival of the street tree is so difficult. The main reason is the small size and poor design of the typical tree pit. The design of the pit is crucial to giving the tree a healthy start to life in a tough environment. These design deficiencies are starting to be addressed by experts who are working to create a more hospitable sub-grade environment for the street tree.
The size of the usual tree pit is a key limiting factor for tree growth. Roots are restricted in their growth, limiting the amount of water and nutrients available, as well as compacted too tightly in the soil. Trees, especially large trees, simply need a larger pit for the trees’ root systems to expand into. This is why we often see buckled and broken sidewalks around the base of our city trees.
Another problem is the poor soil condition in the tree pit. The soil composition bears little resemblence to the soil of the forest and should take into account the climatic conditions of the environment and the specific needs of the tree. Soil compaction not only limits the access of air and water to the roots, it contributes to the problem of poor soil drainage. Most street trees die from overly wet soils that may be due to sidewalk runoff or compact soil that causes puddles in the pit. Soil compaction often comes from people walking on top of the pit. Improving soil quality through organic liquid fertilizations, mulching, watering, and cultivating it will increase the life of the tree.
Soil contamination is also very damaging to the tree’s longevity. Deicing salt, petroleum products used to clean the sidewalk, and most problematic, dog waste, are all major contaminants accumulating in the tree pit.
While designed to protect the tree pit and/or tree trunk, the grates and guards ironically end up girdling or killing street trees as the caliper of the tree increases with age. Unfortunately, maintenance of the tree hardware is almost non-existent.
Watering the street tree 15 – 20 gallons a week in the late spring through summer, cultivating and mulching the soil around the tree, pruning the tree, removing guide wires used to stake the tree, curbing your dog, installing tree pit guards to protect the soil from compaction, and removing the top half inch of soil at the end of winter to get rid of the contaminants, are all things people can do to improve the life and quality of the street trees. Get involved, form community coalitions designed to protect the street trees in your neighborhood. It’s worth the effort. We cannot take our trees for granted.
Adapted from the Massachusetts Tree Wardens’ and Foresters’ Association Bark newsletter, May 1998 issue.