Arboriculture & Urban Forestry 45(6): November 2019 Table 10. Street range and means for bulk density (Mg/m-3 Species Bulk density range (Mg/m-3 C. maculata E. polyanthemos L. confertus O. europaea 141–1.58 1.45–1.64 1.28–1.55 1.26–1.50 Mean bulk ) density (Mg/m-3 1.46 1.49 1.45 1.42 ) ) and penetrative resistance (MPa). Penetrative resistance range (MPa) 4.25–4.93 2.70–4.91 1.34–3.66 1.05–1.85 249 Mean penetrative resistance (MPa) 4.68 3.89 1.92 1.53 Table 11. Variance components bulk density and penetrative resistance. Measurement Bulk density Penetrative resistance Street 10.8% 21.9% Address within street 30.1% 32.8% Direction within address 59.1% 45.3% a tree (Table 11). The penetrative resistance data were similar to those for bulk density, with most of the variability being for samples taken around the same tree, indicated by direction within an address. The Chlorophyll Fluorescence (Fv/Fm) for E. polyanthemos (0.83) and O. europaea (0.78) was within the range of a healthy tree. C. maculata, L. confertus, and Q. palustris had Fv/Fm readings just under 0.78, and REML analyses showed the majority of Fv/Fm variability was between the compass readings of the one tree. DISCUSSION After analysis, the eight species were placed into three categories. Category 1 (C. maculata and E. polyan- themos) trees increased growth in compacted soil, were more tolerant of soil compaction, and may not require soil amelioration prior to planting. Category 2 (C. sempervirens, Q. palustris, and W. floribunda) trees had growth unaffected by compacted soil, were tolerant of soil compaction, but may benefit from site amelio- ration to alleviate compaction for optimum growth. They will grow adequately if the soil remains com- pacted. Category 3 (A. littoralis, L. confertus, and O. europaea) trees had reduced growth in compacted soil, did not tolerate soil compaction, and site amelioration would be necessary for growth. These species may not be suitable for compacted soils (Fitzgerald 2012). E. polyanthemos and C. maculata had the highest readings for each of the five measurements (tree height, canopy spread, trunk diameter, canopy mass, and root mass) and both species grew well in compacted and uncompacted soil. E. polyanthemos, L. confertus, O. europaea, Q. palustris, and E. polyanthemos trees were significantly taller in compacted soil. L. confer- tus and O. europaea performed poorly in compacted soils, having significantly greater trunk diameters and canopy widths in uncompacted soil compared to compacted soil. The tallest growing species was E. polyanthemos, while L. confertus was the shortest, with C. maculata, O. europaea, and Q. palustris ranging between. This impacts street tree selection, as rapid height growth is considered desirable, and so E. polyanthemos would be a preferred species choice. Given the tendency of E. polyanthemos and O. europaea to develop wider canopies, which are desirable in street trees, it is worth considering where they are planted in relation to infra- structure and the likelihood of more frequent pruning. C. maculata, C. sempervirens, E. polyanthemos, L. confertus, and Q. palustris had significantly larger canopy mass means compared with root means in compacted soil, suggesting that compacted soil had a negative impact on root growth. All species except A. littoralis had a significant difference between the can- opy and root uncompacted mean mass, and all spe- cies, apart from Q. palustris, had a higher mean canopy mass. Q. palustris had a greater mass below than above ground in both compacted and uncom- pacted soils. This research confirms that C. maculata performs very well as an urban street tree. Many specimens were rated as being in outstanding condition, and it was the only species with a greater root mass in compacted than uncompacted soil, suggesting that it was estab- lishing a substantial root system. E. polyanthemos has the ability to rapidly establish in compacted soil and was the tallest species with the widest canopy and largest trunk diameter. It was a good choice under these con- ditions for a rapid growing, easily-established street ©2019 International Society of Arboriculture
November 2019
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