Arboriculture & Urban Forestry 33(5): September 2007 341 2004 Plymouth Township survey. Five to eight sections were taken from each tree between 1.5 and 21.5 m (4.95 and 71 ft) aboveground with an average sample area of 1.1 (±0.10 SE) m2 [11.8 (±1.1 SE) ft2] per tree. Statistical Analysis All data were tested for normality using the Shapiro-Wilk test (Shapiro and Wilk 1965) and residual plots. Data were not normally distributed after transformations. Therefore, the nonparametric Wilcoxon rank sum test (Ott and Longnecker 2001) was used to determine if the mean number of A. plani- pennis exit holes and woodpecker attack density, percentage of phloem surface area covered by galleries, and percentage of canopy dieback differed significantly between species at each site. Counts of A. planipennis exit holes and woodpecker at- tacks and canopy dieback data from Larned and Butzel in 2003 and Windemere in 2004 were pooled and tested for normality. Data were normally distributed and simple linear regression was used to determine if canopy dieback was a significant predictor of A. planipennis exit hole and wood- pecker attack densities. All analyses were conducted at the P < 0.05 level of significance using SAS statistical software (SAS Institute 2003). RESULTS Green versus White Ash Street Trees At the Butzel site where trees were small, canopy dieback of green ash trees was, on average, 13% to 20% higher than canopy dieback of white ash trees during the 3-year period, but differences were not significant in 2003 (S 83.5; df 1,14; P > 0.0532), 2004 (S 79.0; df 1,14; P > 0.13), or 2005 (S 73.0; df 1,14; P > 0.31) (Fig- ure 1A). Average canopy dieback for green ash and white ash trees increased 32% and 25%, respectively, from 2003 to 2004, and 13% and 18%, respectively, from 2004 to 2005 (Figure 1A). In 2004, canopy dieback, excluding the three dead green ash and one dead white ash trees that were re- moved, averaged 43% (±10.2 SE) for green ash and 30% (±18.2 SE) for white ash. In 2005, canopy dieback (excluding the dead trees) averaged 53% (±11.4 SE) for green ash and 29% (±18.5 SE) for white ash. Green ash trees at Butzel had an average of 17 to 39 more exit holes and woodpecker attacks per m2 (2 to 4 per ft2) than white ash trees throughout the study, but differences were not significant in 2003 (S 80.0; df 1,14; P > 0.11), 2004 (S 47.0; df 1,11; P > 0.27), or 2005 (S 33.0; df 1,8; P > 0.15) (Figure 1B). Exit hole and woodpecker attack densities in green ash more than tripled from 2003 to 2004 and increased fivefold in white ash (Figure 1B). Den- sities remained relatively consistent from 2004 to 2005 (Fig- ure 1B). Average exit hole density ranged from 21 to 78 exit Figure 1. (A) Mean (±SE) percent canopy dieback and (B) mean (±SE) number of Agrilus planipennis exits holes (exits) and woodpecker attacks (WPs) per meter squared for the small green (GR) and white (WH) ash trees at But- zel in 2003, 2004, and 2005. Three dead green ash and three dead white ash trees were removed in 2004 and 2005. Means for canopy dieback include removed trees as having 100% dieback. Means within years were not significantly different between species (Wilcoxon rank sum test; P > 0.05). holes/m2 (2 to 7 per ft2) in green ash and 9 to 43 exit holes/m2 (1 to 4 per ft2) in white ash from 2003 to 2005. Woodpecker attacks were found on both branches and trunks of green and white ash trees. Average woodpecker attack density ranged from 4 to 13 woodpecker attacks/m2 (0.3 to 1.2 per ft2) in green ash and 0 to 10 (0 to 1 per ft2) in white ash over the 3-year period. On average, by 2005, woodpeckers had preyed on 21% of the A. planipennis in these trees. At Larned, green ash trees had significantly more canopy dieback than white ash trees in 2003 (S182.0; df1,20; P < 0.0001), 2004 (S187.0; df1,20; P < 0.0001), and 2005 (S 181.5; df 1,20; P < 0.0001) (Figure 2A). Dieback increased approximately 25% each year for both species and green ash trees averaged 49% to 69% more die- back than white ash trees (Figure 2A). In 2004, canopy die- back was 100% on six of the seven remaining green ash trees and only 10% of the canopy was alive on the other tree. By 2005, all green ash trees in the survey were dead. Green ash trees at Larned had 1.5 to four times as many A. planipennis exit holes and woodpecker attacks per m2 as white ash trees throughout the study. Exit hole and wood- pecker attack densities were significantly greater in green ash ©2007 International Society of Arboriculture
September 2007
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