Arboriculture & Urban Forestry 33(5): September 2007 339 ash (F. nigra), and blue ash (F. quadrangulata) (Barnes and Wagner 1981; FIA 2006). In natural forests, A. plani- pennis could substantially alter biodiversity and stand dynamics (MacFarland and Meyer 2005). Ash trees, particu- larly green ash and white ash, are also commonly planted in many urban areas of the United States (Ottman and Kielbaso 1976; Giedraitis and Kielbaso 1982; Poland and McCullough 2006). Given the extensive damage that A. planipennis has caused to date, an important question is whether A. planipennis pref- erentially feeds or oviposits on certain North American spe- cies of Fraxinus. Understanding the preference hierarchy and underlying mechanisms of A. planipennis attraction among Fraxinus species will increase our ability to accurately assess stand susceptibility to this pest based on species composition. It is also important for developing survey, detection, and management options and predicting spread and impact of A. planipennis throughout North America. To assess host preference, we quantified the density of A. planipennis exit holes and woodpecker attacks at four sites with green and white ash street trees and at two woodlots where white and blue ash trees co-occurred. We also moni- tored canopy dieback and changes in exit hole and wood- pecker attack densities over time. MATERIALS AND METHODS Study Sites Study sites were selected based on four criteria. Each site had to have two species of similarly sized ash trees that were untreated, growing in close proximity under similar site con- ditions, and presumably exposed to similar levels of A. plani- pennis pressure. Permission to survey trees was acquired from the respective property owners. Trees included in our surveys ranged from 4 to 38 cm (1.6 to 15.2 in) in diameter at breast height (dbh) (Table 1). Green versus White Ash Street Trees In 2003, we sampled green and white ash street trees at two sites (Table 1). At the first site, Butzel School in Detroit, Wayne County, Michigan, eight small green ash and eight small white ash trees were growing around the perimeter of the school yard. At the second site on Larned Boulevard, also in Detroit, there were 11 green ash trees on the east side of the street and 11 white ash trees in the grassy median (Table 1). In 2004, we also surveyed seven green ash and seven white ash trees growing in the grass strip between the sidewalk and the street in the Windemere neighborhood in Ann Arbor, Washtenaw County, Michigan (Table 1). The fourth site, sur- veyed during the 2005 season only, included eight green ash and nine white ash trees growing within 30 m (99 ft) of one another near the Lakeside Terraces condominium complex in Sterling Heights, Macomb County, Michigan (Table 1). White versus Blue Ash Woodlot Trees In 2004, we located two woodlots that had established A. planipennis populations and included white and blue ash trees growing in close proximity. In Superior Township, Wash- tenaw County, Michigan, white and blue ash trees ranged from 17 to 32 cm (6.8 to 12.8 in) in dbh and trees were growing 6 to 24 m (19.8 to 79.2 ft) apart (Table 1). In a woodlot in Plymouth Township, Wayne County, Michigan, trees ranged from 11 to 35 cm (4.4 to 14 in) in dbh and trees were growing 3 to 7 m (909 to 23.1 ft) apart (Table 1). Trees in both woodlots were surveyed in 2004 and trees were evalu- ated in Superior Township, again in 2005. Sampling and Data Collection Green versus White Ash Street Trees For each tree, visual estimates of canopy dieback were made annually in late summer, when damage from the current year larvae had become apparent. The cumulative number of Table 1. Number of trees (n) and mean (±SE) diameter at breast height (dbh) for green and white ash trees at four residential sites and blue and white ash trees at two woodlots. Green ashz Site Butzel Larned Windemere Lakeside Superior Twp. Plymouth Twp. Superior Twp. n 8 11 7 8 5 5 4 dbh (cm/in) 8.1 ± 1.2/3.2 ± 0.5 18.0 ± 0.5/7.1 ± 0.2 27.7 ± 2.5/10.9 ± 1.0 32.0 ± 5.3/12.6 ± 2.1 Blue ashy 20.1 ± 3.9/7.9 ± 1.5 22.2 ± 3.7/8.7 ± 1.5 21.2 ± 2.4/8.3 ± 0.9 zThe same trees were resurveyed each year. yTrees were felled for sampling and new trees were selected each year. ©2007 International Society of Arboriculture 4 5 4 n 8 11 7 9 White ashz dbh (cm/in) 4.2 ± 0.2/1.7 ± 0.1 23.3 ± 0.7/9.2 ± 0.3 23.3 ± 1.3/9.2 ± 0.5 33.0 ± 4.7/13.0 ± 1.9 White ashy 20.6 ± 2.4/8.1 ± 0.9 24.2 ± 4.6/9.5 ± 1.8 23.4 ± 4.0/9.2 ± 1.6 2004 2004 2005 Survey year(s) 2003, 2004, 2005 2003, 2004, 2005 2004, 2005 2005
September 2007
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