Arboriculture & Urban Forestry 47(3): May 2021 delivered 2.0 kg (4.5 lb) of nitrogen per 92.9 m2 (1,000 ft2 125 ) each time the trees were fertilized. The trees were mulched with hardwood bark to a depth of 5.0 cm (2 in) in a circular ring 0.91 m (3 ft) out from the trunk. The trees received only natural rainfall during the test. One-half of the trees received structural pruning while the other half were not structurally pruned. The structural pruning treatment included (1) removal of broken, dead, and dying branches; (2) establishment of a dominant leader (subordinate upright branches were removed as needed to reduce codominance); (3) removal of branches such that the branches that remained were spaced vertically 7.5 cm to 15 cm (3 in to 6 in) apart in a spiral pattern vertically on the trunk; (4) removal of clusters of branches emanating from the trunk; and (5) removal of lower branches on the trunk to a distance of 1.4 m (4.5 ft) above the soil surface. The pruning treatment occurred in years 2 to 4 following planting. The pruning practices imple- mented generally conform with industry standards (American National Standards Institute 2017; Lilly et al. 2019). Throughout the testing period from 2012 to 2018 (7 years), trees were measured for their diameter at breast height (DBH) at 1.37 m (4.5 ft) above ground. Measurements of tree height and width were taken with a 7.62-m (25-ft) Leveling Telescoping Rod (CST/Berger, Mount Prospect, IL, USA). Tree dimen- sions and their change from initial size to year 7 were compared between sites and treatments using a Gen- eral Linear Model with Tukey pairwise comparison at a 95% confidence interval to account for the unequal population sizes wrought by losses over time and site plantation differences. During the 7-year growing period, fire blight dis- ease (Erwinia amylovora) was the only pest observed infecting the plants. The infection only occurred in a few plants to a limited extent. Observations on the ‘Redspire’ cultivar indicate a range of susceptibility, from resistant (SelecTree 2020), to light to moderate susceptibility (Gilman and Watson 1994), to quite susceptible to fire blight (Dirr 1998). During the 7 years of planting, none of the tree branches were broken naturally by high winds or ice storms. This required the breaking of stems using artificial means. Twenty-two random trees, one-half structurally pruned and one-half not structurally pruned, were cut down from the northern Ohio site and transported to The Davey Tree Research Farm on 2 August 2019. Limb breakage tests were conducted during one week at the 2019 Tree Biomechanics Week at The Davey Tree Research Farm located at 6220 State Route 303, Ravenna, Ohio. Each tree was sectioned to isolate trunk sections extending 0.30 m (1 ft) above and 0.30 m (1 ft) below a targeted branch union. The branch axis was retained. One branch was chosen in the lower canopy (LC) to capture the first or second lateral branch from the ground at 1.5 m (5 ft). The second branch chosen was higher in the canopy (HC), 0.4 m to 1.4 m (1.5 ft to 4.5 ft) above the lower tested branch union section. To determine moisture content at the time of load testing, wood samples (whole disk from a 2.5-cm to 10.2-cm [1-in to 4-in] section) were taken on the trunk above and below the branch connection and a branch sample beyond the branch collar zone. Dry weight was determined by oven drying wood cross-sectional samples at 101 °C (214 °F) until constant mass was obtained. Moisture content data was calculated by sample (wet mass − dry mass)/dry mass. A data set was developed on live trees at the same northern planting site for comparison. Tree samples were coded for the time between cutting the tree and the time of load testing. Lower branches were tested as a group before upper branches in the first data set. The result was a temporal series of: • Lower branches tested 5 to 7 days post-harvest • Upper branches tested 7 to 9 days post-harvest • Second field set tested as live (pre-harvest) Moisture data was broken into one-way ANOVA with Tukey separation on whole-sample average mois- ture as a temporal series of unequal sizes, and in a one-way ANOVA with equal sample sizes to com- pare sample position (trunk below, trunk above, and branch). Finally, a pairing process was attempted to match post-harvest and pre-harvest testing pairs based on trunk-branch aspect ratio, angle of departure, and branch diameter. A freestanding metal device (Figure 1) was used for the branch breaking test (Goodfellow et al. 2013). A 2.5-cm to 7.6-cm (1-ft to 3-ft) long trunk with a branch attached was strapped vertically to the metal frame. The branch to be broken was connected to a 2,000-lb (907-kg) capacity Optima Scale Tension/ Compression Crane Scale with digital weight indica- tor (Model #OP-926-2K, #OP 019A, Northern Tool & Equipment, Burnsville, MN, USA). The scale was ©2021 International Society of Arboriculture
May 2021
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