Development and assessment of ash mortality models in relation to emerald ash borer infestation

Abstract

Emerald ash borer is a pest of North American ash that has caused significant mortality within its introduced range. The timeline for tree mortality, once infested by emerald ash borer, is variable for individual trees, with a small proportion surviving infestation. Using tree health assessments and signs of emerald ash borer infestation, researchers developed decision models to predict the probability of mortality. Two resulting models performed well at correctly predicting mortality (>83% correct) and significantly separating probability of mortality for those trees. Both models used diameter at breast height (DBH) and presence of bark splits, with one including percent crown dieback and the other including vigor rating (overall tree health assessment). A third model had reduced correct prediction of mortality, but was still potentially an effective model. Other tested models had shortcomings in prediction of mortality or in separation of probabilities of mortality. Using variables from three potential decision models, the year of mortality was modeled. However, specific year prediction was not as effective. Because of a wide range of external factors, prediction of a specific year of mortality may not be appropriate. Using DBH and rapid health and infestation assessment data, the authors were able to correctly predict ash mortality within a three-year period for the majority of trees within this study. Management strategies that use these models for developing hierarchical removal programs for infested ash may distribute financial and environmental costs over multiple years as opposed to mass removal of street and park trees.