248 Gilman et al.: Impact of Stabilization and Production Method on Anchorage and Growth stake. A second Arbortie was secured to the trunk and to the other stake in an identical manner. The guying system (GS) used was Arbortie strap- ping tied to short stakes (0.62 m long, 38 mm × 38 mm, non-treated dimensional lumber) driven 0.46 m into ground. Lumber was installed on a 30-degree angle to vertical so that bottom of stake was closer to the trunk than the top. Strapping was tied to the trunk with a non-slip knot just above a branch cluster as close to 1.4 m from ground as possible. The other end of the strapping was tied to the short stakes and secured with a screw to pre- vent slippage. Three stakes were positioned 120 degrees apart with two on the south side and one to north. Previous research showed that winching direction had no impact on bending stress required to cause tree or system failure (Ekstein 2007). The root-ball stabilization system (TT) was the Terra Toggle™ (Accuplastics Inc., Brooks- ville, Florida, U.S.). Two 3.8 cm × 8.9 cm (2 × 4 nominally dimensional lumber) untreated pine boards were placed on the root ball parallel to one another at 5 cm from and tangent to the trunk on opposite sides. Lumber was cut to the same length as the width of the root ball. One Terra Toggle Earth Anchor was driven 1.2 m into the ground at each end of each piece of lumber at approxi- mately a ten degree angle from vertical away from the tree using a water jet driving tool provided by the manufacturer. Earth Anchors were tied to low-stretch 25 mm wide plastic strapping that secured the lumber tightly to the top of the ball. Two straps were connected with a metal buckle on top of the lumber, and slack was removed with a strapping tool supplied by the manufacturer. All systems were illustrated in Ekstein (2007). Trees were winched so the cable remained paral- lel to ground. The cable was pulled at 2 cm • second-1 until the trunk base tilted five degrees, and then the cable was let slack. The trunk angle was recorded during winching. One minute later, the tree was pulled to ten degrees, let slack, and the trunk tilt angle was recorded as the rest angle aſter letting the cable go slack. Data from load cell and inclinometer was collected at 2 Hz by Data Acquisition System (National Instruments Corporation, Austin, Texas, U.S.). Data were displayed in real time, during pull- ing tests, on a laptop running LabView soſtware (v: 7.0; National Instruments, Austin, Texas, U.S.). Trunk bending stress at position of inclinometer at one, five, and ten degrees was calculated accord- ing to Equation 1 (Gilman and Masters 2010). Equation 01 where 𝜎𝜎弶ﭒ = 𝐹𝐹弶ﭒ ∙𝑑𝑑弶ﭒ ∙𝑅𝑅弶ﭒ 𝜋𝜋弶ﭒ 4∙𝑅𝑅弶ﭒ 4 σ = bending stress F = pulling force d = distance from pulling point to inclinometer R = trunk radius (calculated as halving di- ameter measured with a diameter tape at inclinometer) Winching Trees All trees were winched due north on 6–12 April 2010, with a cable and electric winch mounted on a tractor to evaluate lateral stability (Gilman and Mas- ters 2010). An inclinometer (model N4; Rieker Inc., Aston, Pennsylvania, U.S.) was mounted to a fabricat- ed steel plate (5.1 cm × 7.6 cm). The plate was strapped to the trunk base 15 cm from the soil surface, which was just above the swollen root collar. A 3,629 kg ca- pacity load cell (SSM-AF-8000; Interface Inc., Scott- sdale, Arizona, U.S.) was placed in line with a pulling cable attached to the trunk 1.7 m above ground. ©2016 International Society of Arboriculture Growth Data Collection The initial trunk diameter was measured 15 cm from the ground on 30 March 2009. Trunk diameter and tree height were measured 30 September 2009. Root balls were dug from the ground immediately aſter winching on 14 April 2010, and all roots cut at 5 cm beyond the edge of the original circular root ball. The diameter of the trunk and all roots greater than 2.5 mm diameter in the top 25 cm of the soil profile were measured at the cut surface. Measurements were in- dependently collected in four 90-degree quadrants: leeward (north), windward (south), east, and west. Experimental Design and Data Analysis The design was a randomized complete block in five blocks of eight trees. Each stabilization system (four systems) was installed on one tree of each nurs- ery production method (two methods, container and field grown) for a total of 4 × 2 = 8 trees per block. All trees in a block were pulled on the same day. Data were analyzed using SAS as a random- ized complete block design with nursery produc-
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