Tsuga canadensis

Tsuga canadensis occurs from Ontario to Nova Scotia south to Maryland and eastern Minnesota, and along the Appalachian mountains to Georgia and Alabama. This species has declined, most severely in the southern Appalachians, due to mortality caused by the Hemlock Wooly Adelgid (Adelges tsugae), an exotic pest. The Conservation Status of this species should be reviewed frequently to detect changes in the impact of the pest.

Tsuga canadensis occurs from Ontario to Nova Scotia south to Maryland and eastern Minnesota, and along the Appalachian mountains to Georgia and Alabama (Fernald 1950, Kartesz 1999).

A serious threat to the species is the hemlock woolly adelgid (Adelges tsugae (Annand, 1928)), an insect that is believed to have originated in Japan and first detected in North America in the 1950s. The adelgid, found in 19 states and 2 provinces, has caused mortality in Canadian and Carolina hemlocks throughout the Appalachian region, especially in the south, but also as far north as southern Maine, Michigan, Nova Scotia, and Ontario (Ellison et al. 2018, Cohn 1993). The most serious declines are found in the southern Appalachian Mountains, areas of the mid-Atlantic region, and southern New England (Ellison et al. 2018). The adelgid is a chronic problem, as it can infect all ages of trees. Trees that are attacked can die in several years, but most die slowly over a decade. Mortality is variable, from 0 to 99% (Ellison et al. 2018, Souto and Shields 1999). A related threat is "preemptive logging" which may be occurring well outside the insect's present range (Foster 1999). In Canada, the spread of the adelgid is being carefully monitored; when it is found, eradication is attempted (Fidgen et al. 2015). Nova Scotia is experiencing declines due to the adelgid (Emilson and Stastny 2019). The habitat shift after infestation to deciduous hardwoods, as well as pre-emptive logging to prevent spread of the adelgid, which also causes a habitat shift, contribute to an environment that is not conducive to the regeneration of the species.

In addition to the adelgid, the non-native Elongate Hemlock Scale is also stressing the species (Miller-Pierce et al. 2019). The introduced Spongy Moth (Lymantria dispar) also attack hemlocks, and a recent study has shown that Spongy Moths feed preferentially on branches and leaves infected with adelgid (Kinahan et al. 2019).