Arboriculture & Urban Forestry 39(6): November 2013 ciency. Consequently, tree roots at roadsides could be trapped be- tween the concrete surface above and poor soil below (Jim 2001). In this study, researchers compared three standard street planting techniques used in Manchester, UK. The first tech- nique was the conventional method in which trees are planted in small cutout pits with topsoil. The other two techniques in- clude trees planted with increased rooting volume and com- paction reduction mechanisms and sealed with permeable seal- ing. Fifteen Pyrus calleryana ‘Chanticleer’ trees were planted in these three pit types. The objective of this study was to test the effectiveness of these pit designs and soil composition in respect to the growth, stress tolerance and cooling potential- ity of a commonly planted street tree P. calleryana. To do this, researchers measured aspects of tree growth, stress levels, and transpiration on hot summers days over three growing seasons. METHODS Study Site The study was carried out in Greater Manchester, UK, which is a large conurbation (population 2.5 m) located in the northwest of England (Armson et al. 2012). It has a temperate maritime climate with a mean annual temperature of 9.8°C and annual pre- cipitation of 806.6 mm. Among the studied years, 2012 was sig- nificantly wetter (1089 mm of rainfall) than 2011 (817 mm) and 2010 (796 mm). Rainfall measurements were collected from the Whitworth Observatory 400 m north of the experimental street. In conjunction with the Red Rose Forest, a community for- estry group, researchers selected Dilworth Street (53°27’47”N, 2°14’3”W) as the field site since it represents a true urban setting with residential buildings on one side and commer- cial buildings and a university parking lot on the other. The street is paved in black asphalt, bordered by concrete sidewalks (3–4 m wide) running from east (closed end – access to one of the University of Manchester parking lot) to west (Cecil Street), and is 7 m wide. It was also easily accessible for the subsequent measure- ments and comparatively secure. Fifteen Pyrus calleryana ‘Chanticleer’ root ball (40 cm × 45 cm) trees with circumference of 14–16 cm at 1 m from ground, and 4–4.5 m in height were planted in April 2010 in three types of pit installations. In the nursery (Barcham Trees PLC, Cambridgeshire, UK) bare-rooted trees were lifted as from the field and re-grown in 65 L containers for 12 months and only bottom branches were pruned. At the time of planting, all trees had comparable vigor and vitality. Type 1 (open) pit trees were planted in 1.5 m2 cutout pits in the pavement and filled with stone-free topsoil—a sandy loam in structure with 15%– 18% clay, 20%–22% silt, and 60%–65% sand content but no additional measures were taken to reduce compaction. In Type 2 (small covered) pits, additional 50% coarse sand was added to topsoil in the pit to reduce the compaction, and the pit was sealed with permeable paving on 257 top. Finally, to increase the rooting volume and reduce the com- paction, an interlocking root cell system filled with topsoil was used in the bigger pit size (Type 3, large covered pit) (Table 1). The schematic diagram of the three types of pit is shown in Figure 1. The trees were all protected by steel tree guards 1800 mm high and 500 mm in diameter. In addition, a pair of treated softwood stakes (2.4 m tall × 75 mm diameter) were also in- stalled in all three types of pits, and trees were secured to the stakes at approximately 1600 mm height using the twin stake and belt method. Trees were planted around 7–10 m apart from each other with the pit next to the curb. To reduce any bias in conditions, trees were planted in order in five groups, in each of which, trees growing in each type of pit was installed one after another. Nine trees were planted on the south side of the street, while the other six were planted on the north. At the north side, the buildings were far from the boundary line; therefore, trees were not shaded at any time of the day. However, along the south side, there were buildings that were approximately 7–8 m tall (two story) and 9–10 m distance from the boundary line, mean- ing that the trees were partially shaded at some point of the day. Continuous monitoring of street level conditions was not possible; instead, sequences of diurnal measurements were made over three growing seasons. Observations were made during the following periods: April–November 2010, March–November 2011, and March–November 2012. As part of aftercare, the contractor watered each tree with approximately 23 L of water at around 1 week intervals start- ing from the middle of April to the middle of May in 2010 and 2011. Water was given on the open surface of Type 1 pits and in the irrigation pipes for Type 2 and Type 3 pits. Figure 1. Cross-sectional design of the three pit types (adapted from tree planting design for Red Rose Forest, drawn by Ombler Iwanowski Architects). ©2013 International Society of Arboriculture
November 2013
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