124 Rathjens et al: Structural Pruning in Callery Pear Does Not Change Union Strength in Seventh Year Load Test strength. However, research has shown that this is not the case (MacDaniels 1932; Miller 1959; Lilly and Sydnor 1995; Gilman 2003; Dahle et al. 2006; Kane et al. 2008). The best predictor of branch attachment strength is aspect ratio (Gilman 2003; Kane 2007; Kane et al. 2008). Aspect ratio is defined as the size of a branch or stem relative to its parent, measured just beyond the union (American National Standards Institute 2017). Strong branch attachment occurs when the diameter of the tree trunk or parent branch is larger than the diameter of the smaller branch (Far- rell 2003; Gilman 2003; Harris et al. 2004). More specifically, the branches should be less than 2/3 the size of the trunk from which the branch union arises (Farrell 2003). However, trees with included bark are weaker in branch union strength (Smiley 2003). Included bark is bark that becomes embedded in a union between branch and trunk or between codomi- nant stems that causes weak union strength (ISA International Dictionary 2019). The material properties of wood are known to have an inverse relationship with moisture content (MC). Wood below fiber saturation point (MC < 30% to 35%) is stiffer and stronger than green wood (MC > 35%)(Cousins 1976, 1978; Cannell and Morgan 1987; Kane 2007; Kane and Clouston 2008; Kane 2014; Dahle et al. 2017b), and when MC is above 50%, material properties tend to remain constant (Lavers 1983; Kretschmann 2010; Spatz and Pfisterer 2013). Researchers have utilized static load trials on intact branch unions in the field to understand failure behavior (MacDaniels 1932; Miller 1959; Lilly and Sydnor 1995; Gilman 2003; Dahle et al. 2006), and some have employed static load tests in a laboratory setting after removing the branch unions from the tree (Kane et al. 2008; Eckenrode 2017). If MC were to change greatly or drop below 50%, the results of test- ing in the laboratory may be different than in situ. Eckenrode (2017) reported that MC was greater than 50% when testing within 2 days, and Kane et al. (2008) reported that MC stayed above fiber saturation when testing within 45 days. While some of these studies utilized protective measures to slow moisture loss, it remains unclear how long a sample will remain at field MC levels. Structural pruning is the elimination of branches and stems to influence the orientation, spacing, growth rate, strength of attachment, and ultimate size of branches and stems. Likewise, structural pruning is ©2021 International Society of Arboriculture performed on small- to medium-sized trees to create a lasting trunk and branch arrangement (Gilman and Lilly 2008). The objective of this research was to determine if there is an effect from structural pruning of young ‘Redspire’ pear trees on branch union strength during early crown development. In addition, ‘Respire’ pear was monitored for growth during the test period to record impacts on tree dimension over time. Lastly, the interval between tree harvest and breakage testing strength was noted by testing moisture levels. This was performed to determine if wood moisture content influenced the branch strength and if there was a criti- cal timing element in the harvest time moisture response which would limit study results and interpretation. MATERIALS AND METHODS To increase the chances of subjecting trees to storm events, ‘Redspire’ Callery pear trees were planted in three locations in Ohio (USA) in the spring of 2011. The first location was at The Davey Nursery at 5509 Congress Road, Wooster, Ohio. This area was desig- nated as the northern Ohio planting site. The soil was a fine-loamy, mixed, active, mesic Aquic Fragiudalfs (Canfield sandy loam). The second location, or the central Ohio location, was at Columbus State Commu- nity College, Delaware Campus, at 5100 Cornerstone Drive, Delaware, Ohio. The soil was a combination of a fine, illitic, mesic Aeric Epiaqualf (Blount silt loam) and a fine, illitic, mesic Aquic Hapludalf (Glyn- wood silt loam). The third site was in southern Ohio at the Spring Grove Cemetery and Arboretum, 4521 Spring Grove Avenue, Cincinnati, Ohio. The soil was a fine-silty, mixed, active, mesic Oxyaquic Fragiu- dalfs (Cincinnati silt loam). A total of 45 branched trees 1.8 m (6 ft) tall were planted in the spring of 2011 at each location. Trees were planted in an orchard grid on a 4.6-m (15-ft) spacing. The planting areas were mowed monthly, fertil- ized once every 2 years, and mulched once every 3 years. The trees were fertilized with 30-10-7 slow- release fertilizer (Davey Arbor Green ProR , The Davey Tree Expert Company, Kent, OH, USA). The fertilizer was mixed with water and applied below ground under hydraulic pressure 0.10 m to 0.30 m (4 in to 12 in) deep. Injections were made at 0.91-m (3-ft) intervals underneath the tree canopy using the standard liquid injection technique for trees. This
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