Download or read book Effects of Community Structure on Forest Susceptibility and Response to the Emerald Ash Borer Invasion of the Huron River Watershed in Southeast Michigan written by Annemarie Smith and published by . This book was released on 2006 with total page 244 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Emerald ash borer (EAB) (Agrilusplanipennis Fairmare) is an exotic, wood- boring beetle that has killed millions of ash trees (Fraxinus species) in southeastern Michigan. If not contained and eradicated this invasive insect has the potential to devastate ash throughout North America causing substantial economic and ecological consequences. The objectives of this research were to (1) determine if community composition, diversity, and stand structure influence susceptibility of forests to EAB invasion, and (2) determine how EAB-induced ash mortality may influence forest community composition. Plots were established during the summers of 2004 and 2005 in 31 forest stands within the Huron River watershed in southeast Michigan that were categorized as xeric (N = 11), mesic (N = 11) or hydric (N = 9). Overstory, understory and seedling tree species composition were quantified in three replicated plots along a transect within each stand. Each ash tree was closely inspected for signs of EAB colonization and degree of dieback. Stem density, basal area, Shannon diversity (H'), relative dominance of ash, relative density of ash, ash importance value, and percent canopy cover were quantified for each stand. EAB has caused significant mortality in all stands across the study area. Dieback of black ash (F. nigra) was more advanced than that of white (F. americana) and green ash (F. pennsylvanica). Percent mortality, percentage of infested stems, and EAB attack frequency were also higher in black ash than the other two species. This difference could be the result of the insect's preference, differences in the physiology of phloem tissue, or an edge effect inherent in riparian and marshy sites to which black ash is adapted. There were no relationships between EAB-induced dieback or mortality and species diversity, stand density, stand basal area, ash basal area, ash density, relative dominance of ash or relative density of ash. Distance from the putative epicenter of the invasion was the only variable that was negatively correlated with all measures of EAB impact. This suggests that it is only a matter of time until all stands suffer complete mortality of Fraxinus species. Widespread loss of ash due to the EAB invasion will initiate changes in community composition and structure in all three forest types. Maple (Acer spp.) and elm (Ulmus spp.) were common on xeric and mesic stands and will likely experience an increase in importance as numerous saplings fill canopy gaps. However, as elms saplings grow they will become susceptible to Dutch elm disease (Chryphonectria parasitica), which is common in the study area. Maple and cherry were over represented in the understory of hydric stands where they should increase in importance. Oaks were poorly represented in the understory layers of all stands and will likely decrease in dominance over the long term. Ash species were common in the sapling layer and were the most abundant species in the seedling layer in all stand types. The high density of juvenile ash may prolong the EAB invasion by providing host material after mature trees are killed. This project documents the initial stages of the invasion of North American forests by EAB. The high susceptibility of all ash species and stands provides clear evidence that EAB has the potential to extirpate ash in North America with ecological impacts similar to those inflicted by Dutch elm disease and chestnut blight. This study also provides baseline data of the community composition of the Huron River watershed at the time of initial EAB colonization, which will facilitate long-term studies of ecological impacts and successional trajectories resulting from of wide-spread gap formation caused by EAB-induced ash mortality.