New Harvard Forest Publication: Ecosystem Response to Hemlock Woolly Adelgid Infestation

Forest ecologist David Orwig, along with several former and current Harvard Forest collaborators, examined the magnitude of ecosystem response associated with 3 years of hemlock woolly adelgid (HWA) infestation in southern New England hemlock forests. The study, published in the Canadian Journal of Forest Research, shows that infested forests had significantly higher HWA-induced foliar loss and significantly lower forest floor C:N ratios and percent soil organic matter than uninfested forests. There were no significant soil temperature differences among stand types, although infested stands did have lower forest floor moisture and higher mineral soil moisture than uninfested stands. Net-nitrogen (N) mineralization and net nitrification rates did not differ between stand types, although net nitrification rates were an order of magnitude higher in infested versus uninfested forests by the third year of this study. In addition, total N pools and NH4 and NO3 captured on resin bags were significantly higher in infested versus uninfested forests throughout this study. These increases in N were likely due to a combination of factors including enhanced decomposition, reduced uptake of both water and nitrogen by declining trees, the absence of understory vegetation, and N-enriched throughfall from infested canopies. These results confirm that invasive pests can initiate substantial changes in ecosystem function soon after infestation occurs, and prior to substantial overstory mortality or understory re-organization.

Orwig, D.A., R.C. Cobb, A.W. D'Amato, M.L. Kizlinzki and D.R. Foster. 2008. Multi-year ecosystem response to hemlock woolly adelgid infestation in southern New England forest. Canadian Journal of Forest Research. 38: 834-843.