78 Gilman et al.: Nursery Planting Depth, Mulch Application, and Root Pruning northern and southern 25% quadrants. Root cross- sectional area (CSA) was calculated from the mean diameter. Other measurements included the fol- lowing: whether the first 10 cm of the root segment growing into landscape soil from the original 170 L container root ball edge was deflected <60 degrees in either azimuth direction relative to the azimuth of its parent root inside the root ball (straight roots); whether the same root segment descended or ascended at < or > 45 degrees relative to the soil surface; distance between soil surface and top of root (root depth) measured 10 cm from 170 L root ball edge; diameter (mean of largest diameter and that perpendicular to it) of the largest root circling at the position of the 170 L container edge; and percentage of total trunk circumference circled with roots >5 mm diameter at any position. Stem xylem water potential was measured one block at a time aſter prolonged, normal, hot, dry, and sunny weather 15 months aſter planting (May 6 and 8, 2009). Irrigation was withheld dur- ing this period. Xylem potential was measured 12:00 to 14:00 hour with a pressure chamber (Soil Moisture Inc., Santa Barbara, California, U.S.) on all 80 trees. Terminal portions (10 cm long) of current year twigs growing in full sun were cut with a hand pruner about half way up the southern side of the crown and were immedi- ately placed in the pressure chamber. Pressure was increased in the air-tight chamber at a constant rate of 30 seconds per MPa. Pressure was recorded when cut stem surface became uniformly wet. Evaluating Anchorage All 80 trees were pulled to the south with a steel cable and electric winch (Model 40764; Chicago Electric Power Tools, Inc., Camarillo, California, U.S.) attached to a tractor in March 2011, February 2012, and May 2013 to evaluate lateral tree stability (anchorage). There was no prevailing wind direction at the site. An electronic incli- nometer (model 3DM-GX1, Microstrain Inc., Vermont, U.S.) was secured with brass screws to the trunk base 15 cm from soil surface, im- mediately above the swollen flare at trunk base. A 3,629 kg capacity load cell (SSM-AF-8000; Interface Inc., Scottsdale, Arizona, U.S.) was placed in-line with the steel pulling cable attached to the trunk about 1 m from ground. ©2015 International Society of Arboriculture The cable was pulled so it remained parallel to the ground at a rate of 2 cm·s-1 until trunk base tilted five degrees (in 2011 and 2012) and to 20 degrees (2013) from the vertical start posi- tion. Trees were held for 60 seconds at five or 20 degrees tilt; when the trunk was released, final trunk tilt was recorded as rest angle. During pulling tests, load cell and inclinometer mea- surements were sampled at 20 Hz using a 16-bit data acquisition system (National Instruments Corporation, Austin, Texas, U.S.) and displayed and archived in realtime on a laptop running LabView soſtware (v: 7.0; National Instruments, Austin, Texas, U.S.). The trunk bending stress was calculated as: (pulling force × distance from pulling point to inclinometer × trunk radius at inclinometer calculated from a diameter tape measurement) ÷ (0.25π × trunk radius4 ). Trunk radius was calculated by halving diameter mea- sured with a diameter tape just before each pull. Experimental Design and Statistical Analysis Experimental design was a randomized complete block design for each taxa separately with eight treatment combinations assigned at random to five blocks for a total of 40 trees/taxa. Eight treat- ments resulted from the two planting depths in nursery containers × two root remediation at planting treatments × two mulch treatments aſter planting. Taxa were planted in adjacent plots and analyzed independently. Repeated measures three-way ANOVA was used to analyze differ- ences between levels of main effects and inter- actions. Means for main effects were separated with Tukey’s multiple range test; those for inter- actions with LSD. Time to remove substrate and roots was compared with a t-test. Pearson’s Cor- relation Coefficients were calculated between root measurements and bending stress. Signifi- cance was assessed at P < 0.05 unless indicated. RESULTS Shoot and Root Response None of the three factors tested impacted stem xylem potential or tree height growth after plant- ing for either taxa (data not shown). Trees of both taxa planted deeply in the nursery container
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