272 Growth Measurements Both height and diameter measurements were made at the end of the nine-year study period. Nails were used to mark the location of the graft union at planting. This reference point was used to help adjust the measurement height for diameter and to adjust height measurements (i.e., to sepa- rate the impact to height associated with initial starting depth from actual differences in growth). Tree diameter was measured with a diameter tape. Tree height was mea- sured with a measuring pole. Static Pull Tests Static pull tests were conducted in October 2013 to evalu- ate root anchorage. The soil in the test plot was saturated prior to assessment to simulate conditions present during a large-volume rain storm event, as well as to provide con- sistent soil moisture among all trees. Soil survey informa- tion was used to calculate the volume of water required to bring the top 1.2 m (4 ft) of soil up to field capacity using a traveling water wheel sprinkler system. Volumetric soil water content at the soil surface (approximately 5 cm deep) was measured at the time of pull for each tree at a distance of 0.5 m and 1 m from the trunk in the direction of the winch and the direction opposite the winch using a time domain reflectometry (TDR) soil moisture probe (SM150T, Delta-T Devices, Cambridge, United Kingdom). All trees were pulled in the 0° azimuth (due north). To measure trunk tilt, a digital level was secured to the trunk at a height of 15 cm above the soil following the methods described in Smiley (2008). Pull force was measured with a 2,000 kgf capacity dynamometer (Dillon EDX-2T, Fair- mont, Minnesota, United States) placed in-line between the winch cable and a webbing sling that was girth hitched to the trunk at a height between 1 and 2 meters. The verti- cal distance between the soil surface and the pull height was recorded for each tree. The dynamometer had a remote reading device that was placed next to the digital level. This allowed us to use a video camera to record the force and tree tilt simultaneously. The winch, secured to a tractor at a height of 1 m, applied a load to each tree until trees tilted to 5° from the resting position. The winch was stopped, the angle of the winch cable from horizontal was measured with a digital level, and tension was released. After pull tests were completed, videos were down- loaded to a computer for visual analysis. The force required to tilt trees to 1°, 2°, 3°, 4°, and 5° was recorded based on simultaneous readings on the digital level and the dyna- mometer remote communicator. Bending moment (M) was calculated using the formula: M = Pl cosα (1) where P was the applied load, and l was the vertical dis- tance from the soil surface to the pull point (i.e., moment ©2019 International Society of Arboriculture Miesbauer et al.: Impact of Planting Depth on Fraxinus pennsylvanica ‘Patmore’ arm) and α is the angle of the winch cable from horizontal (Ghani et al. 2009; Ow et al. 2010; Gilman and Wiese 2012). An initial correlation matrix was developed that showed a very strong correlation between 1°, 2°, 3°, 4°, and 5° (all correlations were between 0.96 and 0.99), so only the values for 1° were analyzed. Root Excavation After pull tests were completed, root systems were har- vested using a 244-cm (96-in) hydraulic tree spade. Once harvested, the majority of the soil inside the root ball was removed using air excavators (Airspade 2000, Guardair Corporation, Chicopee, MA, United States; X-LT; Super- sonic Air Knife, Inc., Allison Park, PA, United States). Any remaining soil was washed away with water. After soil was removed, all small-diameter roots (i.e., roots < 1 cm in diameter) were identified with a fixed caliper gauge (i.e., a piece of metal with a 1 cm notch cut into it) and removed with a hand pruner. These were oven-dried at 105° C for one week and weighed twice (three days apart) to ensure the samples were fully dried. Of the 32 harvested rootballs, one replicate fell back into its original hole. Having lost access to the contracted hydraulic spade, this was too heavy to retrieve, and the root system was omitted from any analyses below where root volumes and surface area were used to predict stability. Similarly, one of the root sys- tems failed to model properly using the SfM photogram- metry and was also omitted from any analyses related to root volume and surface area. Data Analysis Trees were planted as a completely randomized design with the three discrete planting treatment levels noted ear- lier (i.e., deep planting, moderately deep planting, and proper planting). Analysis of variance was used to assess differences in height, diameter, and the dry weight of small root growth (i.e., all roots under 1 cm in diameter). The lm() function in R (version 3.5.1 [R Core Team 2018]) was used for this analysis. In excavating the roots, we noted that some of the root systems appeared to have settled, while others developed adventitious root flares above the original root flare. As such, we used the root volumes measured at various root depths to predict bending moment. Analysis of variance was then used to assess the impact of initial planting depth on measured root architecture after nine years. Addition- ally, we noted the presence of girdling roots (i.e., roots that are encircling all or part of the trunk base), ascending roots (i.e., deeply originating roots growing toward the soil sur- face), kinked/circling/tangential (i.e., roots growing back toward the trunk but not yet in contact with it) roots (if above the root flare), and adventitious roots. Differences in these defect counts among the three treatments were
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