Arboriculture & Urban Forestry 39(4): July 2013 na, U.S.) was placed in-line with the steel cable attached to the trunk, 1 (smaller trees) to about 2.5 (larger trees) meters from ground. Trees were winched so their cable was parallel to ground by mounting the winch on an adjustable tractor bucket. Winching occurred at 2 cm·s-1 until calculated bending stress was 10,342 kN/m2. This was chosen as the lowest stress because it resulted in very little trunk tilt (about 1 degree) during sev- eral practice pulls on trees from the non-mulched plots. Winch- ing to a constant bending stress was used to simulate exposure to a given wind speed. A stress of 24,132 kN/m2 was chosen as the upper limit because practice pulls showed it resulted in sig- nificant and permanent rotation of root balls as observed in wind storms. Three stresses (13,790; 17,237; and 20,684 kN/m2 ) be- tween these were chosen for a total of five equidistant (orthogo- nal) bending stresses per tree. The tree was held in position at each stress while RP attributes were measured, and then cable was let slack. Trunk tilt (angle change from vertical start posi- tion) was recorded during the winching and 60 seconds after the cable went slack (referred to as resting angle). During winch- ing, load cell and inclinometer measurements were sampled at 20 Hz using a 16-bit data acquisition system (National Instru- ments Corporation, Austin, Texas, U.S.), and displayed and archived in real-time on a laptop running LabView software (v: 7.0; National Instruments, Austin, Texas, U.S.). The trunk bending stress was calculated as: (force × distance from pulling point to inclinometer × trunk radius at inclinometer calculated from a diameter tape measurement) ÷ (0.25π × trunk radius4 As trees were held in position at each stress, several attri- ). butes of the RP were measured within a narrow triangular area defined by 5 degrees either side of the axis of the cable on the windward (away from winch) and winchward (toward the winch) sides. These attributes included distance from the trunk bark at soil line to the lowest point on the winch- ward side (RP hinge point, Figure 6) and highest point on the windward side (RP lift point); and distance from the trunk to the far edge of the soil depression (winchward RP edge), and to the far edge of the lifted plate (windward RP edge). Two brightly colored screws were inserted into the trunk 5 to 7 cm from the ground above the trunk flare, one on the wind- ward and one on the winchward side along the winching axis. Two video cameras pointed at the trunk base were mounted side-by-side near ground level 1 m from the trunk and per- pendicular to the winching axis. Each screw was centered in the viewfinder of the respective camera to record vertical and horizontal distance traveled (displacement) on the winchward and windward side of the trunk. A ruler fixed to the trunk di- rectly above each screw was used as a scale to measure the displacement of each colored screw during video playback. An air excavation device was used in October 2011 to ex- pose roots on the winchward and windward side of each tree in a one-quarter (90 degree) arc centered on the axis of the winching direction. Soil was removed from the edge of the original planted root ball and about 40 cm beyond to a depth of about 20 cm. Diameter of the five largest roots in each arc (10 total per tree) was measured with a micro-caliper 15 cm from the planted root ball edge. Diameter was measured top- to-bottom and side-to-side, and the mean of these two mea- surements was used as the diameter of a circle to calculate cross-sectional area (CSA) of each root. The number of roots (of the 5 largest measured in the two exposed arcs just inside 175 the original root ball edge) that did not appear to be deflected by the container was also recorded for each tree. This was used to calculate the percent of the five largest roots not deflected. Experimental Design and Statistical Analysis The study was designed as a three-way factorial in a random- ized complete block design with 4 container volumes × 2 irri- gation treatments × 2 mulch treatments = 16 trees in each of four blocks. Three-way repeated measures analysis of variance (ANOVA), with time as the within-subjects factor, was used to evaluate impact of main effects and interactions on trunk diameter, tree height, and xylem potential (SAS GLM proce- dure, SAS Institute, Cary, North Carolina, U.S.). Means were separated with LSMEANS procedure. Three-way ANOVA was used to evaluate the impact of main effects and interactions on trunk settlement and trunk cracks; Duncan’s multiple range test (MRT) was used to separate main effects. Trunk CSA, root CSA, percentage of five largest roots not deflected, trunk angle, trunk rest angle, winchward hinge point, winchward plate edge, windward lift point, windward plate edge, and horizontal and vertical trunk displacement during winching were analyzed us- ing two-way repeated measures ANOVA, with bending stress as the within-subjects factor and container volume and irrigation as main effects. Means were separated with LSMEANS. SAS STEPWISE procedure was used to calculate the best predic- tive model of horizontal and vertical trunk displacement from bending stress and various measured tree attributes. Coeffi- cients of determination (R2 ) for the linear relationship between trunk angle and vertical or horizontal trunk displacement dur- ing winching were calculated with SAS GLM procedure. Significant results were reported at P < 0.05 unless indicated. RESULTS AND DISCUSSION Growth and Establishment No interactions among container volume, mulch, and irrigation were significant for any measured parameter. Repeated mea- sures ANOVA showed the main effects of container volume, mulch and irrigation on xylem water potential, trunk diameter, and tree height depended on when the trees were measured. Tree settlement and trunk cracks formed after planting were not affected by irrigation or mulch; however, both were impacted by container volume (Table 1). Settlement distance increased with container volume; trees from the smallest containers (11 L) actu- Table 1. Tree settlement during the first two growing seasons (March 2006 through October 2007) and trunk cracking after planting into field soil from four nursery container volumes. Container volume at planting (L) 11 Settlement: negative number indicates that tree trunk sank into soil in the first 17 months after planting; positive number indicates trees lifted up out of the soil. 103 230 983 z Number in parenthesis indicates range. y Means in a column with a different letter are statistically different at P < 0.05 and were compared with Duncan’s MRT (n = 16, averaged across irrigation and mulch treatments). ©2013 International Society of Arboriculture Tree settlementz (mm) +3 (0 to +16) ay -1 (-5 to 0) a -6 (-16 to 0) b -26 (-32 to -2) c Number of vertical cracks per trunk 0.1 b 0 b 0.1 b 5.3 a
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