36 Gilman et al.: Effect of Container Type and Root Pruning on Root Architecture est roots at the #3 position, reduced the percent- age of circling and ascending roots at the position of the #3 container (Table 4), and reduced (P < 0.0001) the percentage of trunk circumference circled with roots at the #3 position from 57% to 16% as averaged across container types (Fig- ure 1). Root-ball shaving decreased (by nearly half) the diameter of the five largest roots at the position of the #3, while increasing (by 25% or more) the diameter of the five largest roots at the periphery of the #15 on the north and south sides of the root ball (Table 4). Number of roots growing straight from the trunk between the #3 and #15 containers and diameter of roots at the periphery of the #15 container were larger on the north than south side of the root ball (Table 5). Root pruning when shiſting #3 trees into #15 containers interacted with container type for two measured root attributes: percent of trunk circled with roots at the #3 position, and number of radial roots between the #3 and #15 container positions. Radial roots were those >2 mm diameter grow- ing straight away from the trunk between the #3 and #15 container positions. Among trees not pruned when shiſted, those in JP had the smallest percentage of trunk circled at the #3 position (Fig- ure 1). Root balls of finished trees in #15 SS and RT not shaved had a similar percentage of trunk circled by roots at the position of the #3 con- tainer; and trees in both had a larger percentage of the trunk circled with roots than in all others. Root pruning reduced the percentage of trunk circled with roots for all container types, but the amount varied (Figure 1). For example, pruning #3 RB reduced circling roots by a little less than 50%, compared to not pruning; whereas, prun- ing AP or JP nearly eliminated circling roots. Trees in JP and SP had the most radial roots among trees not root pruned when shiſted (Fig- ure 2); trees not root pruned in SS had the fewest radial roots. For all container types, except JP, root-ball shaving increased the number of radial roots, but the amount depended on the container type. For example, shaving nearly doubled radial root number in FN and SS, whereas increases were smaller for other containers, such as CR and SP. As further evidence of interaction between root-ball shaving and container type, trees in non-shaved JP and SP had as many radial roots as those in shaved CR, RB, RT, and SS (Figure 2). Table 4. Effects of root pruning #3 root balls when shifting ‘Florida Flame’ red maple into #15 containers on attributes of harvested trees in #15 containers. Root pruningz None cull at #3 container mm diameter over root roots at #3 container positiony % trees graded as % trees with roots >5 collar within #3 78 au Shaved 23 b container dimensions 48 a 27 b 12.7 a 6.9 b Diameter five largest position (mm)x Diameter of five largest roots on northern periphery of #15 root ball (mm)w 4.5 b 6.0 a Diameter of five largest roots on southern periphery of #15 root ball (mm)w 4.2 b 5.2 a z Shaving removed the outer 3 cm of the root ball periphery and bottom. Trees in #3 and 15 containers for 7 and 9 months, respectively. y Based on roots in the top 5 cm of root ball according to Florida Grades and Standards for Nursery Plants (Anonymous 2015); a cull occurs when there is one (or more) root greater than one-tenth the trunk diameter in the top half of the root ball growing more than one-third around the root ball. x Roots measured at the position of the #3 container, before descending, circling, kinking, ascending, or growing straight into #15 substrate. w Roots in the outer 3 cm in the north or south 180 degree circumference of root ball. v Percentage (54%) descending plus kinked roots was not changed by root pruning. u Means in a column with a different letter are statistically different at P < 0.01; n = 40, averaged across eight container types due to insignificant interaction (P > 0.07). Table 5. Root attributes in the north and south half of harvested #15 and #45 red maple root balls. Cardinal direction No. of radial roots in #15z North 180 degrees South 180 degrees 30 aw 27 b containers for 7, 9, and 15 months, respectively. y No. of radial roots in #45y 64 ax 51 b Diameter of five largest roots on #15 root ball periphery (mm)x 5.8 a 4.8 b x Roots in the outer 3 cm in the north or south half of root ball; no other root attributes were significant. w Means in a column with a different letter are statistically different at P < 0.01; n = 80, averaged across container type and root pruning due to insignificant interac- tions (P > 0.10). % of five largest roots at #3 container position in the top half of root ball that eitherv Circled 40 a 18 b Ascended 6 a 1 b Diameter of five largest roots on #45 root ball periphery (mm)x 6.7 a 5.7 b z Number of roots >2 mm diameter growing straight (with less than a 45 degree turn) from trunk between #3 and #15 container position. Trees in #3, #15, and #45 Number of roots >2 mm diameter growing straight (with less than a 45 degree turn) from trunk between #15 and #45 container position. ©2016 International Society of Arboriculture
January 2016
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