The emerald ash borer (Agrilus planipennis Fairmaire, Coleoptera: Buprestidae, EAB) is a wood-boring beetle native to Asia. Ash trees (Fraxinus spp.) are killed by larval feeding in the phloem and cambium; this disrupts the flow of water and nutrients and eventually girdles the tree. Though EAB was identified near Detroit, Michigan in 2002, this insect has been present in Michigan forests for almost two decades. Tens of millions of ash trees have been killed by EAB during this period. The effects of EAB in forest ecosystems, particularly within riparian forests, are largely unknown. Forest inventory and land cover data were used to assess the impacts of emerald ash borer introduction on riparian forest ecosystems in Michigan, USA.
Ash trees are a major overstory component of Michigan’s riparian forests. Between 1993 and 2004, statewide estimates of ash mortality totaled 6.6 million cubic feet per year, 48 percent of which occurred in riparian forests. By 2008, there was a 3-fold increase as the mortality of ash climbed to 18.7 million cubic feet per year. While there was a small decrease in overall mortality in riparian forests between 2004 and 2008, riparian ash mortality increased by 92 percent during the same period. Analysis of riparian forests in the Southern Lower Peninsula showed a marked decrease in the amount of ash trees between 2004 and 2008 with a loss of nearly 15 million trees. This study provides evidence of changes within riparian ecosystems over the time period that coincides with the introduction of EAB and its subsequent infestation.