Document: DAV-3-63-19

Ecosystem response to hemlock decline from hemlock woolly adelgid in southern New England.

ORWIG, D.A.*, R.C.COBB, M.L.KIZLINSKI, S.J.CURRIE and D.R.FOSTER

Harvard University, Petersham, MA 01366-0068 ¹

Abstract:
Selective elimination of dominant tree species by introduced forest pests may initiate dramatic changes in forest structure, composition, and ecosystem function. To examine ecosystem response to stress and mortality on hemlock (Tsuga canadensis), by the introduced hemlock woolly adelgid (Adelges tsugae, HWA) we investigated the timing, magnitude and duration of nitrogen cycling changes in 8 sites in southern New England that vary in the level of HWA infestation. We analyzed nitrogen with close-topped cores, in relation to microenvironmental changes in soil temperature and moisture and light (through hemispherical photographs) as stands deteriorated. Thinning canopies from heavy HWA damage resulted in increased light and decreased forest floor moisture content. Soil water content in the forest floor was strongly associated with percent open sky (R² =0.79). In comparison with healthy forests, heavily infested sites tended to have higher net N mineralization rates, larger extractable NH₄-N pools, and had net nitrification rates 25 times greater. Low and undamaged stands typically showed net immobilization of nitrate. Results indicate that introduced pests and selective tree decline can rapidly and dramatically alter ecosystem processes even prior to the onset of extensive tree mortality.

Keywords: ecosystem function, hemlock woolly adelgid, forest pests, nitrogen cycling

This abstract is being presented at: 8:00 AM in session:
Oral Session #44: Terrestrial Invertebrates: Foodwebs and Plant Responses.