In the April 2000, issue of Grounds Maintenance this article was published. Does anyone have more details on the study?
U.S. cities spend more than $135 million annually to repair what is believed to be tree-related damage to infrastructure. Cracked and raised sidewalks constitute a major portion of this. But are trees really to blame? That's -been the assumption, which is why efforts to reduce sidewalk failures focus on sidewalk-friendly species, root barriers and other tactics. However, a group of Ohio researchers has questioned this assumption and come up with some surprising information.
The investigators evaluated hundreds of sidewalks in Cincinnati, Ohio, for signs of failure. Rated by standard criteria used by the Cincinnati public works department, blocks were considered to have failed if they were cracked, broken or off set more than 3/8 inch. The researchers noted the presence or absence of adjacent trees, the age of the sidewalks (from city records) and whether the underlying soils were rated as having slight, moderate or severe limitations for construction purposes.
The investigators found that the percentage of sidewalk blocks cracked or raised was higher for blocks without trees adjacent to them, regardless of age of the sidewalk. They also found that on newer sidewalks, some blocks were raised, but none by adjacent trees.
As for soil type, they discovered that soils with moderate to severe limitations for construction were associated with greater rates of sidewalk failure than soils with only slight limitations. Based on these results, trees are minor contributors to sidewalk failures. The soil's suitability for sidewalk construction seems to have a bearing on failure rates.
Although some trees were associated with damage, all such instances occurred with sidewalks that were more than 20 years old. Cincinnati constructs sidewalks to specifications that should yield an average of 20 to 25 years of life. Thus, these sidewalks, from an engineering standpoint, did not fail prematurely. It is tempting to conclude that the sidewalks could've lasted even longer in the absence of trees, but the older sidewalks in this study without adjacent trees had even higher failure rates.
These findings should force us to reconsider the assumption that trees are a primary cause of sidewalk failure. This only prevents investigation into other causes of sidewalk failures.
<Scott Culen>
Posted
Reply to post by Tom Dunlap, on June 24, 2000 at 20:37:11:
Journal of Arboriculture Volume 26: Number 1 January 2000
TREES ARE NOT THE ROOT OF SIDEWALK PROBLEMS by T. Davis Sydnor, David Gamstetter, Joan Nichols, Bert Bishop, Jammie Favorite, Cherelle Blazer, and Leslie Turpin
