FOREST RESPONSE TO THE INTRODUCED HEMLOCK WOOLLY ADELGID IN SOUTHERN NEW-ENGLAND, USA

Hemlock woolly adelgid (HWA), Adelges tsugae, an introduced aphid-like insect from Asia, is expanding its range across the northeastern Unit ed States through the range of Tsuga canadensis (eastern hemlock) and can severely reduce or eliminate this important late-successional spec ies. As part of a study investigating stand-and landscape-level forest dynamics resulting from HWA infestation, we examined initial communit y response of eight T. canadensis stands in south-central Connecticut. Our major objectives were to assess mortality patterns in T. canadens is, evaluate subsequent changes in stand microenvironment, and relate these and stand composition to initial patterns of regeneration, under story response, and community reorganization. Tsuga canadensis damage varied broadly across the study area ranging from near zero to greater than 95% mortality. All size and age classes sampled were attacked by HWA, although smaller trees exhibited higher mortality rates than lar ger trees. All remaining T. canadensis sampled in seven of the eight s tands were infested with HWA and over 90% suffered at least 50% foliar loss. Substantial accumulations of downed woody debris have developed in stands with severe HWA damage. Canopy gaps created by HWA damage s ignificantly increased the amount of light reaching the forest floor a nd resulted in rapid understory vegetation responses. Prolific Betula lenta (black birch) establishment occurred in stands with moderate to severe T. canadensis mortality. In addition, opportunistic herbaceous species (Erechtites hieracifolia, Phytolacca americana) and exotic spe cies (Ailanthus altissima, Microstegium vimineum) have recently invade d these stands. Due to mortality from HWA, T. canadensis seedlings wer e scarce in sampled stands, suggesting that advance regeneration and s eedbanks will not be important mechanisms for T. canadensis reestablis hment. Tsuga canadensis cannot sprout following defoliation and has no apparent resistance to HWA. Therefore, dramatic reductions in T. cana densis across broad geographical areas appear imminent if HWA dispersa l continues unimpeded and no effective natural enemies of HWA are foun d.