Comparative studies on the identification and assessment of basal stem necrosis in ash trees (Fraxinus excelsior) against the backdrop of the European ash dieback

Abstract This study deals with ash monitoring data collected by the FraxForFuture research network on 14 intensive monitoring plots across Germany. It focuses on the phenomenon of ash dieback in Germany. As basal stem necrosis has been identified as the main cause of ash dieback and uprooting, early detection is essential. To this end, this study investigated three different methods for detecting stem collar necrosis, which we applied simultaneously and compared in the intensive monitoring plot in Brandenburg. We assessed a cohort of 1,572 ash trees distributed across the 14 plots six times over a three-year period using a nationally standardized ash dieback assessment key. In addition, we assessed 29 ash trees on the Brandenburg plot using a resistograph. Of these trees, we subjected 19 to intensive biochemical analysis. These methods were then evaluated and compared. Our analysis of the scores shows significant variation in the incidence and progression of basal stem necrosis across Germany. Comparison with the resistograph indicates limitations in the detection of severe necrosis by scoring alone. Biochemical analysis highlights the effect of necrosis on soluble carbohydrate and total phenolic content, with soluble amino acids also implicated. As ash dieback progresses, ash trees, which are often severely damaged in the canopy, need to be thoroughly assessed at the base of the trunk to limit damage and minimise loss of value.