Arboriculture & Urban Forestry 41(2): March 2015 Before planting, 10 trees of each nursery planting depth and species (10 × 2 × 2 = 40 trees total) were air excavated as deep as possible (approximately 10 cm) to expose the point where the structural roots emerged from the trunk (root collar). Roots positioned over the collar (either crossing over structural roots, tangent to, or circling the trunk) were removed with hand pruners to the edge of the 170 L root ball. Roots were cut by the same person with a hand saw or pruners before they deflected— where possible—in an attempt to encourage new roots to grow from the cuts radially away from the trunk. This was not always possible because some cut roots had grown upward within the root ball, resulting in the cut surface facing the sky. More- over, roots growing against the trunk were difficult to cut at the ideal position—however they were cut—because they were partially embedded in the trunk. Roots that were deflected by the 11.4 L, 57 L, and 170 L containers but not growing over the col- lar were cut just proximal to the deflected portion of the root. A second air excavation and root prun- ing was required to remove the remaining substrate and roots over the collar and main structural roots; this was conducted immediately following the first. Total time to remove roots (root remediation) on each root ball was recorded. The remaining 20 trees of both taxa (40 trees total) were not root remediated when planting into the landscape. Holes 10 to 15 cm wider than root balls were dug with straight sides and flat bottoms and adjusted so the top of the root ball was about 5 cm higher than the surrounding landscape soil surface. One person tamped the bottom of holes by foot to standardize settling. Once the root ball was placed in the plant- ing hole a 15 cm wide volume of undisturbed soil at the edge of hole was loosened and pushed into the hole. The rest of the void around the root ball was filled with soil removed from the planting hole. Water was added to settle backfill soil, and soil was packed firmly by foot to standardize compaction. No berm or water ring was constructed around the root balls. Weeds were controlled with periodic (three to four) annual applications of Glyphosate (isopropylamine salt, 41%) down each row. Trees were planted on 2.4 m centers in rows 3 m apart and stabilized with two pieces of non-treated lum- ber (3.8 cm × 5.3 cm × 50 cm long, Terra Toggle, root ball stabilization system, Accuplastics Inc., 77 Brooksville, Florida, U.S.) secured to earth anchors in June 2008; they were removed June 2009. Wood chip mulch from local line-clearance operations, typically consisting of leaves, twigs, and chipped wood, was applied 12 cm deep before set- tling in a 1.8 m wide strip down all rows. Mulch was withheld from the top of the root ball on half the trees of each taxa that were root remediated and from half the trees that were not (40 trees total); remaining trees (40 trees) were mulched to within 5 cm of the trunk resulting in 7 cm over the root ball. Root collar and roots exposed by the root remediation treatment were leſt exposed to the atmosphere; they were covered by 7 cm of mulch in the mulch to the trunk treatment. Mulch was not managed in any way other than a reap- plication in April 2010 to original dimensions. Trees were irrigated with 20 L applied over the root ball three times weekly until November 3, 2010, when irrigation ceased. One Roberts Spot- Spitters (Roberts Irrigation Products, Inc., San Marcos, Idaho, U.S.) positioned at the edge of the root ball directed water toward the trunk. Trees were fertilized with 400 g of 16-4-8 applied to the root ball surface March and June 2008 and 2009, and with 400 g 20-0-8 March and May 2010, and March 2011. Trees were not pruned aſter plant- ing into the landscape other than to remove small diameter drooping branches for mower clearance. Evaluating Growth and Health Trunk diameter 30 cm above ground was measured at planting (February 2008) and every October thereaf- ter through 2012. Tree height was measured at plant- ing and October 2008 and 2009. Percentage of trunk circumference with visibly sunken and dead bark, evaluated by presence of live woundwood on either side of the dead bark, was measured in March 2009 on the lower 50 cm of the trunk using a diameter tape. Elm trees were dug from the ground (July 2013) with a 122 cm diameter (top of root ball) tree spade, and maples were dug with a hand shovel, to the same dimensions, and liſted with a tractor; soil was washed from the roots. Diameter of all roots >15 mm at the largest point and that perpen- dicular to it was measured with a micro-caliper 10 cm beyond the edge of the original 170 L con- tainer root ball down to the bottom of the original container in a pie-shaped volume representing the ©2015 International Society of Arboriculture
March 2015
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