Article Figures & Data
Figures
- Figure 1.
All city-owned ash trees in Oconomowoc, Wisconsin, U.S. Black stars designate trees that were re-measured for validation. Open circles are all other ash trees assessed by volunteers.
- Figure 2.
Google Maps imagery of Oconomowoc’s ash trees ranked and binned by stress index multiplied by DBH. Low values are healthy trees. High values are stressed trees. Multiplying the stress level by tree size emphasizes larger stressed trees, which may represent more of a public hazard. Dead and missing trees comprise the 11th class.
- Figure 3.
Volunteer and expert a) fine-twig dieback ratings (R2 = 0.736), b) crown transparency (R2 = 0.586), and c) stress index (R2 = 0.527). 1:1 line is solid black. Line of fit is dashed. All relationships significant (α < 0.0001).
- Figure 4.
Cumulative probability distribution of volunteer stress index (black dash) and expert stress index (solid gray). Pairwise comparison (n = 59) shows that values are not significantly different (Wilcoxon Test, P = 0.51). Trees with low stress index values are healthier than trees with higher values.
Tables
Class Definition 1 0%–1% (trace) 2 2%–25% 3 26%–50% 4 51%–75% 5 76%–100% Class % Dieback 1 0%–1% 5 2%–5% 10 6%–10% 15 11%–15% 20 16%–20% 25 21%–25% 30 26%–30% 35 31%–35% 40 36%–40% 45 41%–45% 50 46%–50% 55 51%–55% 60 56%–60% 65 61%–65% 70 66%–70% 75 71%–75% 80 76%–80% 85 81%–85% 90 86%–90% 95 91%–95% 100 96%–100% Class Rubric 1. Tree appears to be in reasonably good health with no major branch mortality or large broken branches. Less than 10% cumulative defoliation, discoloration, and crown dieback is present. 2. 10%–25% cumulative defoliation, discoloration, and crown dieback is present and/or crown area missing based on visual evidence of large broken (not pruned) or dead branches less than 26%. 3. 26%–50% cumulative defoliation, discoloration, and crown dieback is present and/or crown area missing based on visual evidence of large broken (not pruned) or dead branches less than 50%. 4. More than 50% cumulative defoliation, discoloration, and crown dieback is present and/or crown area missing based on visual evidence of large broken (not pruned) or dead branches more than 50%. 5. Tree is dead or missing. - Table 4.
Ranges of DBH, tree health variables, and stress index for all city-owned ash trees and the validation data set re-measured by a tree health assessment expert. Expert versus volunteer mean differences and Wilcoxon P-values. Bolded P-values indicate where expert and volunteer ratings were significantly different (P < 0.05) from each other.
Variable All trees Validation data Expert versus volunteer (n = 316) (n = 64) Mean Wilcoxon min max min max diff. P DBH (cm) 12 124 14 124 0.05 <0.0001 Defoliation 1 3 1 2 −0.46 <0.0001 Discoloration 1 5 1 3 0.10 0.809 Dieback 1% 80% 1% 80% 3% 0.0304 Transparency 6% 62% 6% 61% 5% 0.0001 Vigor 1 5 1 5 0.12 0.2489 Stress index 0.00 3.70 0.00 3.50 0.02 0.638 - Table 5.
Level of agreement between volunteer and expert stress ratings for the same trees (n = 59).
Within Dieback Transparency 5% 59% 34% 10% 76% 58% 15% 76% Within Defoliation Discoloration Vigor 1 class 54% 49% 56% 2 classes 100% 93% 92%
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