International Biological Flora: <i>Tsuga canadensis</i> *

Abstract This account presents information on all aspects of the biology of Tsuga canadensis (L.) Carrière (Eastern Hemlock) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the International Biological Flora : distribution, habitat, communities, responses to biotic factors, responses to the environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history, conservation and management, and global heterogeneity. Tsuga canadensis is a very shade‐tolerant, long‐lived and slow‐growing canopy tree, native to eastern North America but widely planted in cool, humid parts of Europe as an ornamental. In its native range, it is commonly associated with Betula lenta, B. alleghaniensis, Fagus grandifolia , Acer saccharum and in the north Pinus strobus . Its distribution is mainly limited by lack of moisture; consequently, it grows best on moist soils, providing there is good drainage, but will also grow on rocky outcrops and steep eroding soils kept moist by seepage or a moist climate. Reproduction is by seed; both pollination and seed dispersal are by wind. Seedling establishment is best on damp mineral soil or on rotting logs and stumps, which are warmer and moister than deep litter layers of the forest floor. Eastern Hemlock has low value as a forest crop, but it is an important foundation species in the forest due to the habitats it offers directly and through its influence on the forest environment. However, Eastern Hemlock is in decline due to the introduced Woolly Hemlock Adelgid ( Adelges tsugae ; Hemiptera, Adelgidae) which kills developing buds, leading to extensive loss of needles and twigs, and death within 4–20 years. Cold weather can slow the progress of the pest, but global warming is acting against this. Chemical control and biological control using introduced beetles show some promise in isolated stands, but the prognosis is range‐wide decline or extirpation.