178 Gerhold: Crabapple Cultivars As Street Trees Table 1. Size and health ratings of crabapple cultivars planted as street trees, two cultivars paired at most locationsz (continued). Cultivar/abbreviation ‘Snowdrift’/Sn ‘Spring Snow’/SS Sugar Tyme/ST Paired cultivar ASa ASa zC Ce HG Br DW Ce Br Velvet Pillar™/VP zumi ‘Calocarpa’/zC Ce, Md HG Br RJ Ce VP ST Sn Ad Year 6 9 12 12 3 12 12 12 9 12 12 12 12 12 12 12 12 9 Diam. (cm) 6.3 10.0x 12.9x 13.3y 4.3y 11.9 17.5y 23.9y 10.8 20.4y 15.0 9.4x 8.0y 8.4 11.9 14.6 14.9y 7.6x Ht. (m) 4.0 5.0 4.9 4.6 3.4 5.7 5.4y 6.7y 4.2y 5.6y 4.5x 4.0x 3.4x 3.8 4.2x 5.1y 5.2 3.8x Width (m) 3.3 5.0x 5.4x 5.4y — 5.1 5.2x 6.2y 3.4 6.7y 4.8 4.0x 3.4 4.2 4.3 4.7 5.8y 3.6 Foliage (1 to 5) 4.9y 4.8 3.7x 3.4x 3.6y 4.0y 4.6 4.6 3.6x 4.8 4.6 4.0 4.6 4.0 4.7y 3.2x 4.0y 4.7y Branches (1 to 5) 4.8 4.9 4.1 3.8 3.8 4.8 4.9 4.8 4.6 4.9 4.7 4.7 4.7 4.8 4.9 4.8 4.2 4.7 zAverage trunk diameter, tree height, and crown width are in the most advanced year; foliage health and branch health ratings are averaged over all years: 1, 2, 3, 6, 9, and 12 in most cases. ySignificantly greater at 95% level than corresponding value of the paired cultivar. xSignificantly smaller at 95% level than corresponding value of the paired cultivar. Foliage and branch health ratings: 165% to 100% of leaves or branches exhibit injury, 2 45% to 60%, 3 25% to 40%, 4 5% to 20%, 5 less than 5%. An analysis of variance (using MINITAB’s General Linear Model) of quantitative data collected in a given year calcu- lated means and determined statistical differences between the cultivars at a particular location at the 5% level of prob- ability. Each test location in every year constituted a separate experiment with plots providing replication within a commu- nity. These results, along with comments provided by coop- erators, were used to characterize performance of the culti- vars. RESULTS Many of the cultivars paired with each other in a community differed significantly in average tree height, crown width, or trunk diameter (Table 1). All had survival rates of 84% to 100% for the first 3 years and therefore were tolerant of stressful conditions along streets. Twelve years after planting, average tree heights of cultivars in municipalities varied from 3.4 to 6.7 m (11.2 to 22 ft) and crown widths from 3.4 to 7 m (11.2 to 23 ft). The rate of growth in tree height generally was less from the ninth to the 12th year than in the period of most rapid growth, between the third and ninth years (Figure 1); similar patterns of height growth were found for shorter and taller cultivars. The declining rate of height growth indicates that total height probably will not increase much more after the 12th year, although ©2007 International Society of Arboriculture there may be exceptions such as Harvest Gold at Mansfield (Figure 2). The most reliable data are for those cultivars evaluated for the longest time at multiple locations. Comparisons among any cultivars that were not planted together at the same location could be confounded by interaction of culti- vars by locations, i.e., their effects are inseparable. Among those cultivars that had been tested for 12 years in several municipalities, ‘Spring Snow’ and ‘Red Barron’ were the tallest; Brandywine, Harvest Gold, and Madonna were nearly as tall; Centurion and ‘Snowdrift’ were shorter; and Red Jewel and Sugar Tyme were the shortest. Con- cerning the cultivars that have not been tested as long or in as many places, it appears that American Salute™ and Ameri- can Masterpiece will be among the tallest; American Spirit™, ‘Adams’, ‘Sentinel’, ‘Donald Wyman’, zumi ‘Calo- carpa’, Royal Scepter™, ‘Prairifire’, and American Tri- umph™ will be intermediate in height; and ‘Beverly’, Holi- day Gold™, and Velvet Pillar™ will be among the shortest, more or less in that order. Patterns of height growth can vary appreciably among lo- cations as illustrated by four trend lines of Harvest Gold (Figure 2). The trees at Lawrenceville and Mansfield, which are 20 miles apart in northern Pennsylvania, came from the same nursery and were planted in 1993; the cause of the
May 2007
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