Arboriculture & Urban Forestry 46(5): September 2020 327 Table 1. Contribution of strain type to maximum strain at root-stem transition zones and respective orientation at peak applied load during static load tests. Orientation Leeward Windward Tangential n 133 131 132 Strain type (% of location) Tension 3.8% 95.4% 65.2% Compression 96.2% 4.6% 34.8% 96.2% of the reference marks, windward roots had tensile strain in 95.4%, and tangential roots had a mix of both compression and tension strain (Table 1). The 3 root types were not always directly in line with, or tangent to, the direction of pull. Overall mean root divergence from the direction of pull was 18.7°, and there was not a statistically significant difference between mean root divergence for the 3 root directions (P = 0.0649, n = 45). No significant relationships were identified between maximum strain and root divergence for leeward (r 2 (r 2 = 0.01, n = 131), or tangential (r 2 peak load (r 2 = 0.01, n = 369), tree height (r 2 0.02, n = 369), or soil moisture (r 2 = 0.04, n = 133), windward = 0.01, n = 132) orientations. Significant linear regressions were not found between maximum strain and tree factors: DBH (r 2 = 0.02, n = 369), bending moment (r 2 = 0.02, n = 369). = 0.01, n = 369), = Table 2. Mean maximum strain at the reflection point of the root curvature. Mean maximum strain with the same letter were not found to differ using a Tukey HSD compar- ison (alpha 0.05). Strain was analyzed at the inverse square root to correct for normality and presented as a back transformed number. Orientation Leeward Windward Tangential P-value n 15 15 15 Mean strain (%) 0.0910a 0.0911a 0.0492b 0.0012 No significant linear relationship was found between maximum strain and reference marks along the roots, whether overall (r 2 ward (r 2 = 0.04, n = 133), windward (r 2 or tangential (r 2 = 0.02, n = 396) or by root type lee- = 0.01, n = 131), = 0.01, n = 132). Mean maximum strain at the reflection point was found to be lowest in the tangential roots and larger in the leeward and windward roots (P = 0.0012, n = 45, Table 2). Strain regressed against bending moment reflec- tion point at the 5 time intervals was found to have a logarithmic relationship with bending moment for leeward (r 2 (r 2 = 0.27, n = 75, Figure 7) and windward = 0.29, n = 75, Figure 8) orientations. A weaker logarithmic relationship, however, was found for tan- gential roots (r 2 = 0.197, n = 75, Figure 9). Figure 7. Logarithmic relationship between bending moment and strain (1/strain0.5 inverse of the square root of strain is plotted in the graph. ) in leeward roots reflection point. The transformed ©2020 International Society of Arboriculture
September 2020
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