178 Gilman et al.: Impact of Tree Size and Container Volume at Planting, Mulch, and Irrigation Adding to the instability of trees from the larger containers was the dramatically higher ratio of trunk CSA: root CSA measured 15 cm distal to the edge of the planted root ball (Table 2) also re- ported by Gilman and Masters (2010). Sixty-seven to 69 percent of the variation in trunk angle and rest angle was attributed to a combination of the ratio trunk CSA: root CSA, container volume, and bending stress (Equation 1; Equation 2). A portion of the un- explained variation in angle could be due to root system configura- tion within the container root ball, a characteristic that is difficult to measure. Many past studies (e.g., Tanaka et al. 2012) showed that overturning resistance increases with trunk diameter, directly opposite results of the current study. This appeared primarily due to presence of the largest trees in the largest container volumes that had the most deformed root systems as reflected by the least root CSA outside of the planted root ball (Table 2). Increasing trunk tilt with trunk diameter is not unprecedented in that large trees were the most likely to fail in hurricanes (Duryea et al. 2007). Figure 6. Distance between the trunk and the winchward root- soil plate edge, winchward hinge point, windward lift point, and windward plate edge while winching trees to 24,132 kN/m2 bend- ing stresses planted six years earlier from four container volumes (A = 11 L; B = 103 L; C = 230 L; D = 983 L). Different letters in a column for each attribute indicate significant difference (n = 8, averaged across irrigation, P < 0.05). Planted root ball depth is truncated for illustration purposes. [1] Trunk angle during winching = 0.114 (trunk CSA ÷ total root CSA in largest 10 roots) + [(1.32 × 10-9 volume (L)] + [0.0005 × bending stress (kN/m2 = 0.67. 0.0001, R2 [2] CSA largest single root) + [(1.75 × 10-9 × container volume (L)] + [0.0005 × bending stress (kN/m2)] – 5.44; P < 0.0001, R2 Trunk rest angle after winching = 0.025 (trunk CSA ÷ = 0.69. Contributing to good anchorage of trees from smaller contain- ers was the large RP in relation to the trunk diameter. Despite the large differences in trunk diameter (Figure 2), the RP on the windward side was the same length (130 cm) for all container volumes (Figure 6). Previous studies showed that RP depth, shape, and mass were responsible for a significant (13%–45%) portion of overturning resistance (Coutts 1983; Ennos 1995), although roots growing in the windward direction (Stokes 1999) and other factors (Fourcaud et al. 2008) also contribute. More- over, the RP of the smaller containers in the current study was comprised of proportionally more mineral soil than that of larg- er containers (Figure 6) resulting in more mass in the RP of the smaller containers. The strategy of growing roots radially away from the base of the trunk, instead of deflecting down, up, or around, appears best suited for binding together a large mass of soil and roots into a RP that resists overturning of red maple. Although sinking on the winchward side of the trunk increased slightly with bending stress equally for all container volumes (P < 0.01, statistics not shown), trunks only sunk about 3 mm at the highest bending stress (Figure 8). However, horizontal trunk displacement toward the winch increased markedly with con- tainer volume and bending stress (Figure 8). Displacement was considerably more than the 1–5 mm reported in a previous study (Coutts 1983). Lateral displacement reached an average of more than 45 mm at the largest bending stress on the largest two con- tainer volumes (Figure 8), and it was highly correlated with trunk angle during (R2 = 0.81) and immediately after (rest angle, R2 = Figure 7. Exposed root system from trees planted six years earlier from an 11 L container (a) showing many large straight roots, and 983 L (b) container showing large deflected roots close to trunk (left) and only small roots growing into landscape soil (right). ©2013 International Society of Arboriculture 0.89) winching. Decomposition of the organic substrate inside the root ball undoubtedly contributed to weakness, thus allow- ing the trunk to shift (shear) laterally toward the winch and into the deepening depression at the RP hinge point. The deflected nature of roots in larger containers likely accounted for the large amount of horizontal displacement because only a small por- ) × container )] – 5.48; P <
July 2013
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
