By Delaware Center for Horticulture
Wilmington, DE (August 1, 2008)- It seems that homeowners are hesitant to plant large street trees due to concerns about the sidewalk or branches encroaching on their house. Often, they choose to plant smaller trees such as cherries and dogwoods. There is no question that any street tree can beautify the landscape and help the environmental, but are there quantifiable differences between the benefits of large and small trees. We know that all street trees purify the air, absorb stormwater runoff, raise property values, and provide cooling shade that can cut down on energy costs. Yet, there is evidence that larger trees provide multiple times the benefits of small and medium sized trees.
The Center for Urban Forest Research did a study comparing the financial values of small and large trees. They measured the cost savings of certain maintenance activities such as asphalt repaving and sewer plant usage when trees were planted.
They discovered that small trees, such as crepe myrtles, provide about $23 a year in benefits such as stormwater mitigation (decreasing the strain on the sewer system), shading the pavement (increasing the longevity of the road), and cooling the air (less need for air conditioners). But, small trees cost about $14 a year to maintain, so that’s only $9 of net benefits per year, on average. Large trees, such as mature oaks, elms, and maples yield about $55 a year in benefits, while only costing about $18 to maintain. That’s a net benefit of $37.
So, assuming that a small tree will only live for 30 years, that tree will provide about $270 worth of benefits over its lifetime. Large trees, on the other hand, can provide up to $4,400 worth of benefits over a 120-year lifespan. That is 16 times the benefit of a small tree! The conclusion is undeniable: large trees, over time, will save municipalities money.
There is also a method for organizations and individuals to measure the value of trees in their own communities. The STRATUM (Street Tree Management Tool for Urban forest Managers) software uses tree growth and benefit data of predominant urban tree species to calculate the structure, function, value, and management needs of urban forests, all based on existing complete or sample inventories. After running the STRATUM analysis for the street trees in Wilmington, the Tree Program discovered that $988,200 of taxpayer dollars was saved in one year! And just think how much more could be saved if there were more large trees planted, as opposed to smaller ones.
The problem, then, is where to plant large trees. On many existing streets, it simply may not be possible to plant large trees due to narrow sidewalks or overhead power lines. But, we should not succumb to the limited space argument so easily. A lot of the time, there are ways around such restrictions.
Large trees can be pruned away from buildings and power lines. A lot of homeowners and city officials are also hesitant to plant large trees because they fear the sidewalk will eventually crack. This is a concern, but it can be overcome. Sidewalks, or at least the area around the tree, could be done with removable pavers. Another thing to do is to dig larger tree pits. Larger tree pits and tree lawns leave more room for the roots to grow and make it less likely that they will bulge through the sidewalk and create a hazard.
If you are thinking about planting a tree on your property, consider planting a large tree. If done properly, the costs to maintain the tree will be significantly less than the benefits, especially if the tree is shading your house and keeping it cool. Tell your neighbors too!
For more information, visit the Delaware Center for Horticulture.