Comparison of beech bark disease distribution and impacts in Michigan from 2002 to 2011

Beech Bark Disease (BBD) has spread across much of the northern range of American Beech since its arrival in eastern Canada around 1890. The nonindigenous beech scale, Cryptoccus fagisuga Lind., colonizes the outer bark of beech trees, facilitating the entry of the cambium-killing Neonectria spp. pathogen. Infestations of beech scale were first identified in one Lower and one Upper Michigan County in 2000. In 2002-03, impact plots were established in 62 sites in twenty-two counties, representing stands that were uninfested, lightly infested, and heavily infested with beech scale. At that time, impacts of BBD were minimal and data represent pre-BBD conditions. In 2010-11, we revisited the 62 impact plots to quantify current beech scale densities, overstory condition, understory vegetation and down woody debris. Current conditions were compared to variables recorded in 2002-03 to assess effects of BBD on stand composition, productivity and wildlife-related variables. Since 2002, scale densities have increased across all infested locations and many uninfested sites are now infested. The advancing front or beech scale has spread from the original discovery in two counties to 24 counties in 2011. Heavy infestations around roads and campsites suggest that human traffic plays a role in beech scale distribution. High beech mortality was observed in areas with heavy beech scale which were associated with edges or roadsides. Beech mortality rates in Lower Michigan are substantially lower than in Upper Michigan.