Life History and Disturbance Response of Thuja occidentalis (northern white-cedar)
Family: Cupressaceae
Guild: persistent, slow-growing understory tolerant
Functional Lifeform: medium-size evergreen tree
Ecological Role: grows in pure stands or conifer-hardwood mixtures in swamps or on low stream borders, moist pastures, or abandoned fields; withstands long periods of suppression and responds well to release
Lifespan, yrs (typical/max): 300/400
Shade Tolerance: tolerant
Height, m: 15-20
Canopy Tree: yes
Pollination Agent: wind
Seeding, yrs (begins/optimal/declines): 6/75/300
Mast Frequency, yrs: 2-5
New Cohorts Source: seeds or layerings
Flowering Dates: late spring
Flowers/Cones Damaged by Frost: no
Seedfall Begins: early fall
Seed Banking: 5 yrs +
Cold Stratification Required: yes
Seed Type/Dispersal Distance/Agent: winged/ to 100 m/ wind
Season of Germination: spring and summer
Seedling Rooting System: variable
Sprouting: layering common
Establishment Seedbed Preferences:
Substrate: mineral soil, decayed wood, moss
Light: open with protective shade
Moisture: moist required
Temperature: warm
Disturbance response:
Fire: Northern white-cedar stands are initiated by high-intensity crown fires that occur during dry, windy weather at intervals of centuries or more. Fire serves to remove competition and also removes the forest floor moss layer that dries out in the summer and prevents seedling establishment. The probability of fire on most northern white-cedar sites is low, but fires occasionally originate on drier sites and spread into northern white-cedar stands. Many northern white-cedar forests in the Lake States originated after fire. If the peat burns and the humus is destroyed, northern white-cedar may not become established for a long time. Thin-barked and with volatile foliage, it is highly susceptible to fire-caused mortality. Large trees may survive very low-intensity fires. Frequent fires may exclude northern white-cedar from some sites. It is highly resistant to decay. It reproduces well on moist organic soils exposed by fire if a seed source is nearby. Prescribed fire is recommended to aid in regeneration after harvest unless there is ample advance regeneration or if the organic soil is unsaturated. Fire removes the heavy slash that prevents regeneration and also prepares a favorable seedbed. Annual, low-intensity prescribed fires ignited in the autumn can be used to eliminate northern white-cedar that invades fens in the absence of fire.
Weather: Northern white-cedar is intolerant of flooding and susceptible to ice and snow damage. In exposed conditions, it is susceptible to drying during droughty winters. Older trees are susceptible to windthrow.
Air pollution: Northern white-cedar is tolerant to ozone and sulphur dioxide. No symptoms of foliar injury have been noted in areas of high ambient ozone.