30 Gilman et al.: Retention Time in Nursery Containers and Root Pruning at Planting anchorage six (08–10 November 2010) and 18 (14–16 November 2011) months after landscape planting. Trees were winched three rain-free days, after the last measurable rainfall, with an electric winch attached to a cable about 1.2 m from the ground. The cable remained parallel to ground. A 3,629 kg capacity load cell (SSM-AF-8000; Inter- face Inc., Scottsdale, Arizona, U.S.) was placed in-line with the winching cable. An inclinometer (model N4; Rieker Inc., Aston, Pennsylvania, U.S.) was mounted to a fabricated steel plate (5.1 cm × 7.6 cm). The plate was secured to trunk base 15 cm from the soil surface, which was just above the swollen flare at the trunk base. The cable was winched at 2 cm·sec-1 until the inclinometer tilted five degrees from vertical start position; the tree was held for 60 seconds, while the dis- tance was measured from the trunk to the deepest point of the soil depression on the leeward side (referred to as hinge point) before relaxing the cable. Final angle at the trunk base was recorded as rest angle 60 seconds after relaxing cable. Data from the load cell and inclinometer were collected at 2 Hz by Data Acquisition Sys- tem (National Instruments Corporation, Austin, Texas, U.S.) and recorded on a laptop. Data were displayed in real-time during winching on a lap- top running LabView soſtware (v: 7.0; National Instruments, Austin, Texas, U.S.). Trunk bending stress was calculated according to Equation 1. [1] where 𝜎𝜎ሶ蟳 = 𝐹𝐹ሶ蟳 ∙ 𝑑𝑑ሶ蟳 ∙ 𝑅𝑅ሶ蟳 𝜋𝜋ሶ蟳 4 ∙ 𝑅𝑅ሶ蟳 4 σ = bending stress F = pulling force d = distance from pulling point to inclinometer R = trunk radius (calculated as halving diameter measured with a diameter tape at the inclinometer position) In June 2014, an air excavation device removed soil from the top 10 cm of the soil profile within a 60 cm radius around each trunk of all Acer and Magnolia to expose roots. Root measurements included: 1) one visual root imprint rating (1 = no imprint on the root system; 5 = large imprint) from root deflection conforming to each individual con- tainer size (11, 57, 170 L), excluding the original ©2017 International Society of Arboriculture propagation container; 2) whether roots forming the imprint either predominantly circled at an angle less than 45 degrees from horizontal (these were circling roots) or predominantly descended at an angle greater than 45 degrees to horizontal (these were descending roots) when deflected at each container size; 3) diameter of the five largest roots measured 5 cm beyond the edge of the planted root ball on the west 90 degree quadrant in the top 10 cm soil profile; and 4) diameter of the three largest roots circling at the position of the 170 L container. Root diameter was converted to cross- sectional area (CSA), assuming roots were circular. Tree height measured from ground to the top of the tree, and trunk diameter using a diameter tape at 30 cm from ground, were collected on all trees at planting and in each subsequent September. Statistical Analysis Trunk diameter over the period of the study was analyzed with repeated measures analysis of variance (ANOVA) in PROC MIXED of SAS (version 9.2). Other measurements on Acer and Magnolia were analyzed separately using PROC ANOVA two-way factorial ANOVA in a random- ized complete block design (4 retention times × 2 root prunings × 5 blocks = 40 trees each taxa), with retention time and root pruning as main fixed effects and block as a random factor. Ulmus was analyzed using one-way ANOVA in a ran- domized complete block design (4 retention times × 5 blocks = 20 trees) with retention time as the main fixed effect. Bending stress and rest angle were evaluated with a split plot in time (No- vember 2010 and 2011) using PROC GLIMMIX in SAS, with the independent variables retention time, root pruning, and year as main fixed fac- tors, and block as a random factor. Results were reported as significant at P < 0.05 unless indi- cated otherwise. Coefficients for regression equa- tions were calculated using PROC GLM in SAS. RESULTS AND DISCUSSION There were no significant interactions between main effects. The main effects (i.e., retention time and root pruning at planting) were significant for at least one measured tree attribute at one point in time.
January 2017
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