D3089: Where’s the beech? Progression and impacts of beech bark disease 20 years after detection in Michigan

Beech bark disease (BBD), an invasive pest complex comprised of sap-feeding beech scale insects (Cryptococcus fagisuga Lind.) and Neonectria spp. fungal pathogens, was first detected in localized areas in Michigan’s Upper Peninsula (UP) and in the northwestern Lower Peninsula (LP) in 2000. Mortality of mature beech caused by BBD can affect an array of wildlife as a result of reduced mast production. Sprouts produced as trees die can result in dense, undesirable beech thickets. In 2002, 62 long-term impact sites were established in the UP and LP in stands representing varying levels of beech basal area and beech scale infestation. Baseline data on beech and other overstory trees, regeneration and coarse woody debris were collected. In 2002, beech scale was established in 23 of the 62 sites and there was no evidence of any BBD-related mortality. When sites were re-visited in 2012, beech scale had invaded 55 sites and as of 2022, 61 of the 62 stands were infested. Some mortality of overstory beech was observed in 2012 in the eastern UP, but beech thickets were rare and beech mortality was minimal in Lower Michigan. To date, we have re-surveyed 46 of the 62 stands; remaining stands will be visited in 2023. Considerable beech mortality has occurred in the UP and portions of the LP. Dead beech accounted for 26% of total beech basal area in the 46 stands surveyed in 2021-2022, while only 6% of beech basal area was dead in these same stands in 2002.