Tree Diversity has Limited Effects on Beech Bark Disease Incidence in American Beech Population of Mont St-Hilaire

Abstract

Background: American beech trees (Fagus gandifolia) exist in many areas in northeastern North America. Beech bark disease (BBD) is caused by a scale insect and bark-killing fungus (Cryptococcus fagisuga and Nectria spp.). We aim to study the correlation between diversity and the presence of BBD, and predict that tree diversity in Gault’s Nature Reserve in Mont St-Hilaire (MSH), Québec decreases the presence of BBD and that F. grandifolia density would increase the presence of this disease. Methods: We randomly chose 15 sites for sampling of individual tree species. F. grandifolia trees were identified as “healthy” or “infected”. Simple regressions, ANOVA, two and three-way interaction, linear mix effect model, and paired t-test were performed using R and Excel. Results: Our results show no significant correlation of infected individuals and total number of either A. saccharum or A. pensylvanica, unless analyzed with a linear mixed effect model (p=0.0256). However, there was a strong, positive correlation between the number of infected trees and the density of F. grandifolia (R2=0.6712), and this relationship was stronger in disturbed areas compared to undisturbed areas in the reserve (t=2.0492, p=0.047, tcritical=2.0211). Conclusion: We found beech tree density and habitat disturbance, but not community diversity, to have a significant positive effect on Beech Bark Disease infection rates.