The invasive emerald ash borer (EAB); (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae), a secondary pest of stressed or declining ash (Fraxinus) trees in its native Asia, is the most destructive forest insect to ever invade North America. Since its arrival in the Detroit metropolitan area in the early 1990’s, EAB has established in 31 states and three Canadian provinces. To date, hundreds of millions of ash trees have been killed and nearly 8 billion trees are threatened in U.S. forests. While all North American ash species are susceptible to EAB, white ash (Fraxinus americana L.) appears to be an intermediate host that is not highly preferred, but still becomes infested and succumbs. Catastrophic levels of ash mortality, ranging from 80% to 99% of stems, were recorded in forested sites located in southeast Michigan and Ohio. Despite these reports, we have observed an unexpectedly high proportion of overstory white ash trees alive in southeast and south central Michigan with the longest history of EAB infestation. To quantify this survival, I intensively surveyed 28 sites in this region. I recorded 821 white ash trees ≥ 10 cm (DBH) in fixed radius plots (18 m) in a 1 ha site. Most (75%) white ash stems are alive and in good condition. More than half (68%) of the live white ash trees had external bark cracks left from previous EAB larval feeding, however, 91% of these trees recovered. In contrast, 95% of the 373 green ash (F. pennsylvanica Marsh.) trees recorded in the 28 sites are dead. This supports findings from previous plantation and urban ash tree studies reporting the preference of green ash trees over white ash trees where they co-occur. Stand-level variables that could predict the percentage of white ash stems and basal area alive were evaluated. White ash stem density and distance from sites to the EAB origin were positively related to white ash survival, while total basal area of all overstory species and white ash were negatively related to white ash survival. Density of white ash stems and distance from sites to the EAB origin were positively related to the proportion of white ash basal area alive. White ash basal area averaged 1.5 ± 0.2 m2·ha–1, and ranged from 0.3 to 3.5 m2·ha–1 within sites, totaling 42.7 m2·ha–1 across sites. I also tallied regeneration and found white ash accounted for 64%, 79%, and 74% of the total recruits, saplings, and seedlings recorded across the 28 sites. Given the impact and ongoing spread of this highly destructive pest, effective monitoring techniques are critical. I established two double decker (DD) trap types in 30 post-invasion sites located in the EAB origin in 2014, 2015, and 2016; one DD comprised of a dark green upper prism and a light purple lower prism (PG) baited with cis-3-hexanol, and one DD comprised of a dark purple prism on top and bottom (PP) baited with cis-3-hexanol and Manuka oil. A total of 580, 585, and 932 EAB adults were captured in 2014, 2015, and 2016, respectively. The PG trap captured significantly more EAB adults than the PP trap. Despite ample live white ash phloem available for EAB development, EAB density has not reached levels high enough to kill trees. In additional to stand-level variables, site variables could also have an influence on white ash survival rates. I delineated a 1.5 km radial buffer from the center point of the 28 white ash sites. Using a combination of downloaded geographic data and data collected during surveys, I fit models at five linear distances (0 to 400 m, 400 to 800 m, 800 to 1200 m, 1200 to 1500 m, and cross-scale). Green ash presence, specifically those growing along roads, had negative effects on white ash survival. The proportion of woody wetlands and the presence of white ash trees, specifically those growing along roads, were also important predictors across multiple distances.
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