Life History & Disturbance Response of Tsuga canadensis eastern hemlock

Family: Pinaceae
Guild: persistent, slow-growing understory tolerant
Functional Lifeform: large evergreen conifer
Ecological Role: grows on cool, moist to very moist well-drained sites; survives for 100 yrs or more in the understory and suppressed trees grow well when released
Lifespan, yrs (typical/max): 450/800
Shade Tolerance: very tolerant
Height, m: 20-30+
Canopy Tree: yes
Pollination Agent: wind
Seeding, yrs (begins/optimal/declines): 20/30/450
Mast Frequency, yrs: 2-3
New Cohorts Source: seeds
Flowering Dates: late spring
Flowers/Cones Damaged by Frost: no
Seedfall Begins: late fall -- winter
Seed Banking: up to 1 yr
Cold Stratification Required: yes
Seed Type/Dispersal Distance/Agent: winged/ to 100 m/ wind
Season of Germination: spring
Seedling Rooting System: variable
Sprouting: does not sprout
Establishment Seedbed Preferences
Substrate: variable
Light: overstory shade
Moisture: moist required
Temperature: warm
Disturbance response:
Fire: Eastern hemlock grows in moist environments and in association with hardwoods that rarely burn. It tends to increase in density with fire suppression. In a strong wind, fires that start in a cutover area, a windfall area, or an area with dead standing timber may carry into stands where hemlocks grow. Seedlings and saplings are killed by even low-intensity fires, but larger trees have some resistance, due to thicker bark. However, eastern hemlocks have shallow roots that are susceptible to fire damage. After several decades, eastern hemlock may invade burned sites. Germination and seedling establishment may be promoted by low-intensity prescribed fires that expose partially decomposed litter but do not kill or topkill overstory itrees that shade the seedbed to prevent drying.
Weather: Eastern hemlocks are extremely susceptible to drought, especially in the seedling stage. They are also susceptible to winter drying on warm, windy days. Heavily thinned stands are susceptible to windthrow.
Air pollution: Eastern hemlock is sensitive to sulphur dioxide, and intermediate to sensitive to ozone. Symptoms of foliar injury have been noted in some areas of high ambient ozone, but not in others; no foliar injury symptoms have been observed after controlled fumigation with ozone. No difference was observed in height growth of seedlings fumigated with ozone under controlled conditions.