Arboriculture & Urban Forestry 40(1): January 2014 diameter circular area around each tree. Shoots were not pruned at or aſter planting. A wood chip (utility pruning waste) mulch layer 10 cm thick was placed across the whole plot, almost up to the trunk, and glyphosate was applied periodically for weed control. In November 2011, all 80 trees were winched with a hand crank that was craſted of a bent steel rod to evaluate lateral stability. No rain occurred during the three days required to pull trees. A force trans- ducer (Model SSM-BYJ-50, 22.7 Kg, Interface Scott- sdale, Arizona, U.S., non-repeatability—±0.02% RO) was placed in line with a non-stretch string secured around the tree with a tightened zip tie at 20 cm from the ground. Trees were pulled at a rate of approxi- mately 10 mm∙sec-1 once in the NE, NW, SE, and SW compass directions to a bending stress (s) of 4.1 MN/ m2 calculated individually for each tree from trunk diameter measured 10 cm from the ground using Equation 1. This slow, winching rate allowed research- ers to pull at the targeted bending stress. This bending stress was chosen so that the trunk nearly returned to the pre-pulling start angle following practice winch- ing, on extra trees from the same group planted nearby, indicating slight root or soil failure. During winching tests, load was sampled at 2 Hz using a 16-bit data acquisition system (National Instruments Corporation, Austin, Texas, U.S.) and displayed and archived in real-time on the laptop running Lab- View soſtware (v: 7.0; National Instruments, Austin, Texas, U.S.). Trunk angle was recorded just prior to each winching by placing a digital level (18 cm long, M-D SmartTool Angle Sensor Module 92346) accu- rate to the tenth of a degree on the bottom 18 cm of trunk on the side opposite the hand crank (wind- ward). A fiſth and final winching to the SW applied a bending stress of 13.8 MN/m2 . With the tree held in position aſter each of the five winchings, the angle under tension and the rest angle following release of the winching string were recorded. The pre-winch- ing trunk angle was subtracted from these angles to calculate change in angle as a result of winching. [1] σ = F • d • R π • R4 4 where σ = bending stress; F = pulling force; d = distance from pulling point to inclinom- eter; and R = trunk radius (calculated as halv- ing diameter measured with a diameter tape). 29 All 80 trees were dug up in December 2011 fol- lowing winching, using a square-tipped shovel forming a circular root ball 40 cm across and 40 cm deep shaped in a cone typical of a tree dug from a field nursery. This shape and volume was large enough to harvest the planted 9.5 L con- tainer root ball intact. Soil and container substrate were washed from roots. Roots were measured for many attributes described in the appropri- ate tables. Root diameter was measured to 0.1 mm; root depth was measured to the nearest mm. Statistical Analysis Root and shoot attributes and bending stress on planted trees in December 2011 were analyzed in a three-way complete factorial analysis of variance (ANOVA) with the main effects propagation con- tainer type (2), root pruning (2), and larger-contain- er wall attributes (2) using 10 replicates each (total 80 trees) in a randomized complete block design using the GLM procedure of SAS (version 9.2 SAS Institute, Cary, North Carolina, U.S.). Duncan’s multiple range test was used to separate main effect means; interac- tion means were compared with Least Squares (LS) means at P < 0.05. Pearson’s correlation coefficient was used to relate root attributes to bending stress. RESULTS AND DISCUSSION Root pruning liners, when shiſting into 3.8 L con- tainers, did not impact aboveground growth aſter landscape planting; however, two measured root attributes were affected. Shaving liners increased cross-sectional area (CSA, calculated from diameter measured just beyond trunk) of straight roots equally for both propagation containers (Table 1). Shaving liners grown in EP had no influence on CSA of de- flected roots because there were few deflected roots to remove (Gilman and Paz 2014); however, shaving SM liners dramatically reduced deflected root CSA compared to not shaving (Table 1) as with red maple (Acer rubrum L., Gilman et al. 2012). Reported effects on crown growth from manual root pruning of trees planted from propagation containers into field soil vary in the literature. Some authors found reduced crown growth (Arnold and Young 1991), no effect (Persson 1978; Gilman and Wiese 2012), or greater growth (Krasowski and Owens 2000) following root pruning at planting. Although trunk angle during winching was not impacted by root pruning the lin- ©2014 International Society of Arboriculture
January 2014
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