Detection, Description and Treatment of Girdling Roots on Urban Norway Maple Treesi

--Girdling roots are examined and described on streetside Norway maple trees (Acer platanoides L.) in Ann Arbor, Michigan. Treatments consisting of cutting girdling roots, fertilizing and pruning foliage were evaluated after two years and found to be of no benefit to girdled trees. From August 1977 to August 1979 this study was made on 410 Norway maple trees (Acer platanoides L.) planted between 1925 and 1928 on the sidewalk extensions in the west-central section of the City of Ann Arbor, Michigan. The objectives of the study were to 1) evaluate the degree to which girdling roots affect Norway maples growing along streets in this area; 2) gain information on the characteristics of girdling roots, such as diameter, number per tree, depth, degree and severity of girdling and relative percentages of surface and subsurface occurrence; 3) identify and evaluate the effects of factors that contribute to the formation of girdling roots; 4) determine if treatments of fertilizing and trimming benefit girdled trees after two growing seasons; 5) determine if removal of girdling roots affect the health and vigor of trees; and 6) confirm the most effective measures for evaluating the effects of treatments. GIRDLING ROOT CHARACTERISTICS Thirty-five percent of the girdled trees were girdled by only one root, 46 percent were girdled by 2 to 3 roots and 19 percent were girdled by 4 to 9 roots. The mean diameter of all girdling roots was 2.5 inches (6.4 centimeters). Surface girdling roots have a significantly larger mean diameter than subsurface girdling roots (3.38 vs. 2.22 inches [8.59 vs. 5.64 centimeters]). On the average, 2.4 girdling roots were found on each girdled tree. Seventy-three percent of the girdling roots were subsurface. The mean depth of subsurface girdling roots was 2.5 inches (6.4 centimeters), and 79 percent of them were found within 3 inches (7.6 centimeters) of the ground surface. There was no grafting between girdling roots and trunks. 'Metro. Tree Impr. Alliance (METRIA) Proc. 3:83-87, 1980.