106 Persad and Tobin: Evaluation of Tree Symptoms Associated with EAB ratio = 1.7; 95% CI = 1.4, 2.1), while branch frac- tures at the branch tip were significantly associated with trees that were not positively identified with EAB (risk ratio = 0.7; 95% CI = 0.5, 0.9) (Figure 2D). The absence of branch fractures (risk ratio = 0.9; 0; 95% CI = 0.7, 1.1), and branch fractures at the center of gravity (risk ratio = 1.0; 95% CI = 0.6, 1.4), were not significantly associated with EAB detection. It is noteworthy that researchers failed to detect a significant effect of the proportion of canopy loss (risk ratio = 1.0; 95% CI = 0.9, 1.1), and the presence of epicormic branching (risk ratio = 1.1; 95% CI = 0.8, 1.4). Both are generic indicators of tree decline from various stress agents, including EAB. Because many of the selected trees, due to the objective of the study, were visually uninfested or only thought to be recently infested (i.e., Level I or II), trees had not yet formed epicormic branching that is typical of trees heavily infested with EAB (McCullough et al. 2008). Indeed, although epicormic branching was observed in 158 trees in which EAB was positively identified, researchers also observed 174 trees with epicormic branching in which EAB was not positively identified, and 387 trees with no epicormic branching. Also, although non- infested trees tended to have little or no canopy loss, while high levels of canopy loss were mostly from infested trees, a number of infested trees were also detected in which little to no canopy loss was recorded (Figure 3). However, in a follow-up analysis on canopy loss, in which trees were placed into one of two categories: 1) trees in which the canopy loss was ≤30%, and 2) trees in which the canopy loss was >30%, we detected a significant association; the presence of >30% canopy loss was significantly associated with trees positively identi- fied with EAB (risk ratio = 1.8; 95% CI = 1.5, 2.1). Figure 3. Distribution of the number of trees (N = 719) by the pro- portion of canopy loss and whether EAB was visibly detected (i.e., trees that were either negative or false negative for EAB). DISCUSSION Figure 2. Mosaic plots of the percentage of trees where EAB was positively identified (grey bars) or not positively identi- fied (white bars) based on the absence or presence of (A) bark loss or (B) scaffold cracks; (C) absence or presence of branch fractures within the lower (L), middle (M), or upper (U) one-third of the canopy; and (D) the location of the frac- ture point of the branch, if present: at the union with the stem (Union), branch center of gravity (Cen), or branch tip (Tip). Positive and negative symbols indicate those symp- toms that were significantly positively or negatively associ- ated with the EAB–ash tree complex, respectively, while NS indicates no significant association. In this study, the authors relied on visual, ground surveys of a range of ash trees with different assumed histories of EAB infestation to determine the association of several tree symptoms with the EAB–ash tree complex in urban systems. The overall objective was to determine if cues not previously known to be definitively associated with EAB could be useful in early detection efforts for urban foresters and municipal arborists. The study authors con- tend that these findings should be of use to arborists and other tree workers in identifying EAB-infested trees prior to the associated obvious symptoms, including ash tree canopy thinning and eventual ©2015 International Society of Arboriculture
March 2015
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