160 Armson et al.: Shading Effectiveness of Street Trees in Manchester, UK C. laevigata and Malus ‘Rudolph’ were significantly less elliptical than S. arnoldiana, P. calleryana, and Prunus ‘Umineko’ (Table 2). canopy. In contrast, Malus ‘Rudolph’ had the shortest but wid- est canopy. Because the tallest trees also tended to be the nar- rowest, there were also significant differences in aspect ratio (F4, 46 = 24.91, P ≤ 0.005), post hoc analysis showing that not between the sample dates. Post hoc analysis showed that the C. laevigata and P. calleryana had significantly higher LAI than S. arnoldiana and Prunus ‘Umineko’. Shade area or mid-summer (F4, 46 = 1.366, P = 0.260) (Figure 1b). The shade area cast by each species was not significantly dif- ferent for either early summer (F4, 46 = 1.584, P = 0.195) Air temperatures Mean air temperature was 22.1°C (StD ±4.3) in sun and 22.1°C (StD ±4.3) in tree shade in early summer and 21.9°C (StD ±1.2) in sun and 22°C (StD ±1.2) in shade in mid-summer. One-way ANOVA showed that there were no significant differences between sun and shade temperatures either in early summer (F1, 100 = 0.000, As shade had no effect upon the air temperature no fur- ther analysis of this measurement was carried out. P = 0.987) or mid-summer (F1, 100 = 0.104, P = 0.748). Mean Radiant Temperatures 227.887, P ≤ 0.005) these differences were significant. = 19.315, P ≤ 0.005) and mid-summer (F1, 100 The mean radiant temperatures were 27.7°C (StD ±4.8) in sun and 23.9 (StD ±3.9) in shade in early summer and 28.3°C (StD ±1.9) in sun and 23.7°C (StD ±1.1) in shade in mid- summer, reductions of 3.8°C and 4.6°C due to shade respec- tively. One-way ANOVA showed that in both early sum- mer (F1, 100 = Leaf Area Index There were species differences in LAI (Figure 1a). Two- way ANOVA analysis showed that there were significant differences between species (F4, 92 = 7.48, P ≤ 0.001) but Figure 1. The mean LAI (a) and mean shade area (b) of five different street tree species in Manchester, UK, in early summer and mid- summer 2011: C. laevigata (n = 12), S. arnoldiana (n = 10), Prunus ‘Umineko’ (n = 10), P. calleryana (n = 10), and Malus ‘Rudolph’ (n = 9). For LAI (a), species with the same letters are not signifi- cantly different from each other in both early and mid-summer; no significant differences were found for mean shade area (b) during either sample period. The temperature reductions due to shading by the five tree species are shown in Figure 2a. One-way ANOVA showed that it was only in early summer (Figure 2a) that a significant difference between the species (F4, 46 = 2.613, P = 0.047) could be found, Tukey post hoc analysis showing that C. laevigata reduced mean radiant temperatures significantly more than Prunus ‘Umineko’. Table 2. The mean canopy height, east/west canopy spread, canopy area and aspect ratio produced by five street tree species: C. laevigata (n = 12), S. arnoldiana (n = 10), Prunus ‘Umineko’ (n = 10), P. calleryana (n = 10), and Malus ‘Rudolph’ (n = 9). For each canopy attribute, species with the same letters are not significantly different from each other. Species C. laevigata S. arnoldiana Prunus ‘Umineko’ P. calleryana Malus ‘Rudolph’ Mean canopy height (m) (StErr) 2.828bc (0.121) 3.456abc (0.169) 3.881a (0.337) 3.588ab (0.152) 2.796c (0.075) ©2013 International Society of Arboriculture Mean east/west canopy spread (m) (StErr) 1.915ab (0.100) 1.593bc (0.097) 1.489c (0.063) 1.554c (0.076) 2.076a (0.083) Mean canopy area (m2 3.030ab (0.327) 2.062bc (0.238) 1.914c (0.188) 1.983c (0.195) 3.377a (0.246) ) (StErr) Aspect ratio (StErr) 1.482b (0.072) 2.185b (0.099) 2.486b (0.163) 2.301b (0.091) 1.360a (0.033)
July 2013
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