PS 23-66 - Does lingering ash (Fraxinus spp.) really exist?

Abstract: The introduced emerald ash borer (EAB, Agrilus planipennis) has caused the mortality of millions of ash (Fraxinus spp.) trees in North America over the last two decades, with almost complete mortality of all trees infested by EAB. However, some evidence suggests potential resistance, with survival, by some trees to EAB.



As part of a larger project to monitor EAB-induced mortality of ash and community effects and to explore in situ conservation of ash on the Allegheny National Forest (ANF) in northern Pennsylvania, where EAB was first detected in 2013, we began searching for lingering ash (LA) in Summer 2022. For the purposes of the ash breeding program, LA are defined as untreated ash trees at least 10 cm diameter (dbh) with healthy canopy (AC 1-2) in an area with > 95% ash mortality at least two years ago; however, we are also interested in surviving ash with AC 3-4 to better understand their response to EAB. We used two approaches to locate surviving ash: 1) pre-identified putative LA reported to the ANF; and 2) meander surveys with 30-40 m between people taking 5-6 min acre-1 and in areas known for “complete” ash mortality for at least two years (i.e., south end of ANF). For each LA, we measured dbh, assessed canopy condition, noted insect/disease symptoms, recorded coordinates, took photos, installed a metal numbered tag, and searched the area for other LA.



We located a total of 22 lingering ash (LA, AC 1-4) across the two approaches, with 19 by pre-identification by others or in that vicinity and 3 through meander surveys in 10 stands (total 243 acres, or 98.3 ha). Mean dbh is 31.1 cm (95% CI 24.8 - 39.2 cm), and mean ash canopy condition is 3.0 (95% CI 2.8 - 3.3). All data were reported to the ANF through a 123Survey and to the Great Lakes Basin Forest Health Collaborative (Holden Arboretum) with a shared spreadsheet. These trees will continue to be monitored in the future for potential use in an ash breeding program and to better understand resistance to EAB. Furthermore, we will refine search approaches and then search for additional LA in 2023 – 2024. This work could lead to the conservation of an important and widespread genus of trees in the North American forested landscape.