A modelling approach to assess the long-term impact of beech bark disease in northern hardwood forest

Abstract

This study proposes a modelling approach to assess the effect of beech bark disease on species demographic dynamics and structure of stands using SORTIE, a spatially explicit and individual-based forest succession model. The original model was modified to account for the increased mortality rate of infected Fagus grandifolia Ehrh. (American beech) and for some resistance to the disease. Two different scenarios, modeling species behaviour with and without the disease, respectively, were compared over a period of 300 years. Results reveal significant differences in species global demographic dynamics between both scenarios. Analyses of tree diameter-class distribution indicate that 50 years after the infestation, large F. grandifolia trees disappear, while the number of trees with a DBH between 11 and 50 cm considerably increases. At 300 years, the density of F. grandifolia with a DBH greater than 30 cm in the diseased scenario is superior or close to that in the nondiseased scenario, suggesting a progressive reestablishment of the species population structure. Eastern hemlock (Tsuga canadensis (L.) Carrière) is the species that largely benefits from beech bark disease. The study demonstrates the potential of a modelling approach to acquire quantitative insights about the long-term ecological impact of the disease.