Stand-level factors associated with resurging mortality from eastern larch beetle (Dendroctonus simplex LeConte)

Abstract The current outbreak of eastern larch beetle ( Dendroctonus simplex LeConte) in Minnesota, USA, ongoing since 2000, has been characterized with a severity and duration unprecedented in previous outbreaks within the state. This study investigates the relationship between tamarack mortality due to eastern larch beetle and extant stand and site characteristics. Observations of tree attribute information and site condition collected over the course of the outbreak from nearly 15,000 tamarack trees in three different ecological regions of Minnesota were modeled using linear regression. Increasing tree diameter was the best indicator of tamarack mortality within the northern limits of the state’s tamarack range and during the later portion of the outbreak. Tamarack density was negatively related to tree mortality in the north-central region during the later outbreak, while the density of co-located non-host gymnosperms was positively related to tree mortality in areas of marginal host distribution. A temporal change in the importance of predictor variables suggests that the influence of tree and site characteristics evolved as the outbreak progressed and subsequent mortality increased. A greater understanding of the factors associated with tamarack mortality and how the those factors change over time and space will help to inform management practices and mitigate the impacts of this bark beetle on the tamarack resource in Minnesota.