The Ecological Effects of Beech Bark Disease on American Beech (fagus grandifolia,EHRH) and Northern Hardwood Forests in Michigan

Abstract

Beech bark disease (BBD) was first reported in Michigan in 2000, though experts believe it to have been present in the state for 10-15 years prior to that. The exotic insect/fungal complex is composed of the beech scale (Cryptococcus fagisuga Lind.), and at least one of three species of Nectria fungi. BBD has caused mortality of American beech (Fagus grandifolia Ehrh.) in some of Michigan’s northern hardwood forests, and it is a threat to those forests not yet infested. The purpose of this study was to 1) determine the continuing impacts of beech bark disease on the state’s beech resource, and 2) monitor changes to forest composition and health in disease infested stands. Plots that were first sampled in 2001 were visited again in 2007, and comparisons made on the progress of the disease. Stands visited were divided between the Upper Peninsula and Lower Peninsula. Evidence of disease was noted in 9 plots where it was previously undocumented, showing a pattern of rapid westward movement of the disease. Overall, stands infested with beech bark disease exhibited reduced health (exhibited by poorer levels of foliage transparency, higher levels of crown dieback, and higher severities of damage) and high mortality of beech trees, with a 16% increase in dead basal area in infected areas. The disease is more advances in the Lower Peninsula, likely due to a more recent establishment of the disease there. However, most of the new cases were in the Upper Peninsula. A significant factor contributing to variation in tree and stand condition throughout the state is the wide range of climatic conditions and geomorphologic features over which beech occurs in Michigan.